INTERNATIONAL PRIORITIES AND PERSPECTIVES
Short Plenary Presentations and Panel Discussion
The Fish Health Section of the American Fisheries Society
Organizational and Professional Activities with an International Perspective
Patricia A. Barbash*
U.S. Fish & Wildlife Service, Fish Health Center, Lamar, PA USA Patricia_Barbash@fws.gov
The American Fisheries Society - Fish Health Section (AFS-FHS) is made up of an array of professionals who have provided the framework for modernized diagnostic methodology, disease management, and government regulation. Our membership includes nearly 300 professionals. Although primarily located in the United States and Canada, members originate from eleven other countries worldwide. A third of FHS members are represented by academic professionals and students. More than 60 members represent private industry as practitioners, consultants, diagnosticians, and non-profit research organizations. Approximately 50 members are employed by federal agencies including the U.S. Fish and Wildlife Service, U.S. Geological Survey, National Oceanic and Atmospheric Administration, the U.S. Department of Agriculture, Department of Fisheries and Oceans (Canada), and the Department of Primary Industries (Australia). Many members work for state agencies, tribal organizations, and provincial governments.
The FHS has three primary goals: (a) To maintain an association of persons involved in safe-guarding the health of aquatic animals, (b) To focus attention on aquatic animal health problems by making available appropriate news items, research and educational information, and (c) To stimulate the application of effective aquatic animal health practices by communicating with those entities interested in developing sound aquatic animal health programs. The FHS maintains two professional certification programs, publishes the Journal of Aquatic Animal Health, provides updated information bimonthly through a Listserv Newsletter, and hosts annual meetings along with the ISAAH in North America.
As in all regions of the world, in North America the major threats to wild aquatic resources are also hazardous to cultured populations: exotic and emerging pathogens. Recently we have been challenged by several infectious pathogens that have not only endangered wild populations of fish, but have cost millions of dollars to commercial aquaculture operations as well. The viral agents that cause infectious salmon anemia, spring viremia of carp, and viral hemorrhagic septicemia have played significant roles in diagnostic and regulatory progression, which has been the recent focus of the AFS-FHS collective expertise. Presently, laboratories that provide diagnostic and surveillance services differ widely, from state and provincial labs that operate on constrained budgets to manage local fisheries resources, to government and research labs that are better equipped to focus on national issues. The AFS-Fish Health Section’s Suggested Procedures for the Detection and Identification of Certain Finfish and Shellfish Pathogens (the “Bluebook”) serves as a reliable reference manual to the majority of these facilities, and is cited in a number of state regulations addressing aquatic animal importation and movement. But procedures published in the Bluebook can differ significantly to those in the OIE Aquatic Manual, a document also used for importation/exportation purposes in North America. The National Aquatic Animal Health Plan, finalized with stakeholder input by the USDA, NOAA and USFWS, is in the process of developing a National Aquatic Animal Pathogen Testing Network (NAAPTN) through which diagnostics will be validated for pathogens of concern. The challenge for the AFS-FHS will be to determine how best to integrate Bluebook methodology with those of OIE and NAAPTN, yet remain relevant to all North American aquatic animal health issues.
Asian Fisheries Society - Fish Health Section
Professor, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Tokyo, 108-8477, Japan firstname.lastname@example.org
The Fish Health Section (FHS) of the Asian Fisheries Society (AFS) was formed on 30 January 1989 during the Third Asian Fish Health Network (AFHN) Meeting, held at the Faculty Fisheries and Marine Science, Universiti Pertanian Malaysia (UPM). The Section's goal is to improve regional knowledge on fish health management and to develop awareness among Asian aquaculturists towards establishing a sustainable aquaculture industry.
promote effective interaction and cooperation among persons involved in fish health research;
encourage and promote investigation and advances in knowledge of fish health;
focus attention on fish health problems by disseminating technical and other information on all aspects of fish health; and
promote the proper implementation of effective fish health protection practices in the region.
The Fish Health Sections realizes these objectives by:
holding, on a regular rotational basis, a triennial "Symposium on Diseases in Asian Aquaculture," a meeting of members to discuss broad issues and specific topics related to fish health;
compiling and disseminating proceedings, notes and abstracts of Section-sponsored fish disease conferences and workshops, and other relevant information on fish health to Section members and to the general public;
compiling and submitting a report to the parent Society covering the period since the last Triennial General Meeting, containing a summary of the activities of the Section (in the region), the status of fish health problems, significant progress made towards their control, and recommendations for Society action, as appropriate; and
promoting the development and use of standardized, internationally accepted techniques for the detection and diagnosis of diseases of aquatic animals determined to have regional importance.
Symposium on Diseases in Asian Aquaculture
The Fish Health Section of the Asian Fisheries Society is tasked with publishing both academic and technical information on aquatic animal health as well as promoting the development and use of standardized, internationally accepted techniques for the detection and diagnosis of diseases of aquatic animals of regional importance. The FHS also holds a triennial “Symposium on Diseases in Asian Aquaculture” (DAA) where members and aquatic animal health professionals meet to discuss broad issues and specific topics related to aquatic animal health.
There have been seven previous Symposia, the first one in Bali, Indonesia, 1990; second in Phuket, Thailand, 1993; third in Bangkok, Thailand, 1996; fourth in Cebu, Philippines, 1999; fifth in Gold Coast, Australia, 2002; the sixth in Colombo, Sri Lanka, 2005, and the seventh in Tapei, Taiwan, 2008. Each of these Symposia brought together more than 200 aquatic animal health scientists, students, government researchers and industry personnel from some 30 countries to discuss disease related problems affecting aquaculture production and to find solutions for them. The Eighth Symposium – DAA VIII – is expected to attract many participants from around the world to discuss their work and develop strategies for improving aquatic animal health in Asia. DAA VIII will be held in Mangalore, India.
AFS-FHS Executive Committee (2009-2011):
Chairperson: Professor Chu-Fang Lo (Taiwan), Vice Chairperson: Professor Chadag Vishnumurthy Mohan (India), Secretary/Treasurer: Dr. Suppalak Lewis (Thailand), Past Chairperson: Professor Takashi Aoki (Japan).
Dr. Celia Lavilla-Pitogo (Philippines), Dr. Brian Jones (Australia), Dr. Mangalika Hettiarachchi (Sri Lanka), Mr. Arun Padiyar (India), Dr. Jianhai Xiang (China), Dr. Nguyen Huu Dung (Vietnam), Professor Myung-Joo Oh (Korea)
Official website: http://www.fhs-afs.net
European Association of Fish Pathologists (EAFP)
Sven M. Bergmann*, Stephen W. Feist, David Bruno, Lone Madsen, Roy Palmer and José Garcia
Friedrich-Loeffler-Institut (FLI), German Reference Laboratory for KHVD, Institute of Infectology, Federal Research Institute for Animal Health, Südufer 10, 17493 Greifswald-Insel Riems, Germany email@example.com
The “European Association of Fish Pathologists (EAFP)” was established on October 25th 1979 in Munich, Germany. It represents an interdisciplinary society, embracing all aspects of aquatic disease in fish, shellfish and crustaceans, in aquaculture and in wild stocks. Additionally, amphibians and reptiles are included. Members come from all disciplines, biologists, microbiologists, veterinarians, fish farmers and aquaculture engineers. The objective of the EAFP is to promote the rapid exchange of experience and information on aquatic disease problems and related topics. These aims are pursued mainly through regular regional and international meetings, support for training courses in laboratory techniques and the publication of the Bulletin of the EAFP, a fully citeable journal listed in ASFA, Current Contents and Science Citation Index. The EAFP web site, www.eafp.org provides online access to archive EAFP Bulletins, information on the EAFP conference and other events, workshop reports and a members message board is also available. At the conferences, histological workshops are organised, and the outcome of these workshops are later published on CDs.
Although the EAFP is based in Europe, it welcomes members worldwide and maintains close international contact through a network of Regional Officials called Branch officers. The EAFP has a membership of around 900 from 50 countries. Membership subscriptions include the EAFP Bulletin published six times a year plus access to a regularly updated Members list via the EAFP website.
According to the statutes, the EAFP is served by a President and a five member Council. The EAFP is organised into national branches. These activities are co-ordinated by the EAFP Branch officers who help to organise local meetings and report on local activities through the Bulletin.
The recent situation regarding mainly virusinduced epidemics in aquatic animals (fish, shellfish, crustaceans) in Europe is characterized by the combat against diseases notifiable by EU but also OIE organised by each EU memberstate. Main topics are recently the combat against “viral haemorrhagic septicaemia (VHS)” caused by a rhabdovirus (genotypes I – III) which infects mainly salmonid fish. While the Scandinavian countries and the UK are free of VHS, the rainbow trout- keeping EU member states in continental Europe are infected. Besides the notifiable diseases such as VHS, IHN and ISA, infections with SAV and IPN are also in focus.
Due to the EU enlargement eastwards, the production of cyprinids is now greater than salmonid production. Therefore, cyprinid diseases like “koi herpesvirus disease (KHVD)”, which infects aquacultured, wild and ornamental fish, became a focus of attention. Besides this disease, a non-notifiable disease (“spring viraemia of carp, SVC”) never disappeared from Europe.
In oyster and mussel aquaculture, the main notifiable diseases are parasitic (marteiliosis, bonamiosis). In 2009 an EU regulation was established due to a new high virulent variant of the “Oyster herpesvirus (OsHV-1)” called “OsHV-1 µvar” which induced severe outbreaks with enomous losses in France, Ireland and the UK.
In European farmed and wild crustacean populations the baculovirus causing “White spot disease (WSD)” is the only non-exotic notifiable disease. However, the fungal “crayfish plague” is also under investigation.
International Association for Aquatic Animal Medicine
Department of Large Animal Clinical Sciences, College of Veterinary Medicine, and Program in Fisheries and Aquatic Sciences, School of Forest Resources and Conservation, University of Florida, P.O. Box 100136 Gainesville, FL 32610-0136 USA firstname.lastname@example.org
The International Association for Aquatic Animal Medicine was founded in 1968. IAAAM was founded to “promote the application of veterinary medicine to aquatic animal disease problems.”
The organization was created by a small group of veterinarians working on captive marine mammals, who wanted to develop a forum to further clinical care of these animals. Since its beginnings it has developed into a group of approximately 500 veterinarians and related professionals who are “professionally involved in the practice of aquatic animal medicine, or in teaching and research in aquatic animal medicine, or in the husbandry and management of aquatic animals”. Although much of the organization’s work involves captive aquatic organisms, and marine mammals in particular, substantial contributions have been made by members of this organization to furthering our understanding of disease processes occurring in wild animals. There is a strong interest in conservation among IAAAM members, and meetings function as important forums where issues of immediate concern can be discussed in an open and collaborative manner. Topic-oriented workshops are typically scheduled in conjunction with the annual meeting. Examples include Oil Spill Response training held in conjunction with the 2005 meeting (Seward, AK) and an Erysipelas workshop held in 2003 (Kona HI). The organization has a strong interest in professional development of students entering the field and fosters their participation through competitive travel grants and awards for quality presentations. The meetings are typically small (<300 participants) and are an excellent venue for students to begin to develop their professional networks.
Kazuo Ogawa1 and Mamoru Yoshimizu2*
1 Department of Aquatic
Bioscience, Graduate School of Agricultural and Life Sciences, The University of Tokyo,
Bunkyo-ku, Tokyo 113-8657, Japan email@example.com
2 Laboratoryof Biotechnology and Microbiology, Faculty of Fisheries Sciences, Hokkaido
Hakodate, Hokkaido 041-8611, Japan firstname.lastname@example.org
In Japan, annual capture fishery production has gradually declined from 5.3 to 4.3 million tons over the last decade (1999-2008), whereas aquaculture production (fish, shellfish and seaweed) has been stable during the same period, fluctuating annually between 1.2 and 1.3 MT. Despite no major change in production, the Japanese aquaculture industry has been adopting different strategies in an effort to obtain higher profits from their products. These include developing disease resistant strains, better quality meat of cultured species, and culturing challenging new species like Pacific bluefin tuna Thunnus orientalis.
Among major disease issues, there is a growing tendency that disease control is more focused on prevention than on treatment. This is evidenced by the development of vaccines against infectious diseases and in the establishment of disease resistant fish strains. Currently vaccines against one viral (red sea bream iridovirus) and four bacterial (Vibrio anguillarum, Lactococcus garvieae, Streptococcus iniae and Photobacterium damselae subsp. piscicida) diseases are commercially available. All vaccines contain inactivated pathogens and no component or DNA vaccine has yet been approved. With the wide use of vaccines to control fish diseases, the use of antibiotics has decreased considerably. Selective breeding of disease-resistant strains of cultured fish have been developed, including lymphocystis disease resistant Japanese flounder Paralichthys olivaceus and IHN resistant rainbow trout Oncorhynchus mykiss. A strain of triploid salmonid, a hybrid of tetraploid rainbow trout and diploid brown trout Salmo trutta, reveals both resistance to IHNV and OMV infection and has better meat quality. Disease outbreaks in hatcheries have been successfully contained, including IHN in salmonids, viral epidermal hyperplasia in flounders, PAV (WSD) in kuruma prawn Penaeus japonicus and amyotrophia of Japanese abalones.
Many infectious pathogens of fish and shellfish have been introduced into Japanese waters by the movement of infected or contaminated eggs and seedlings destined for aquaculture. Beginning in 1996, under the law for conservation of aquatic resources, we have requested that exporting countries issue specific pathogen-free certificates for select diseases of select aquatic animals including SVC and KHV disease for carp Cyprinus carpio, SVC for some cyprinid fish including goldfish Carassius auratus, VHS, EHN, Piscirickettsiosis and Enteric Red Mouth Disease for salmonids, and Nuclear Polyhedrosis Baculoviroses, Yellow Head Disease, IHHN and Taura Syndrome for penaeid shrimp juveniles. Additionally, for the containment of these specified diseases once the disease is introduced, the law for sustainable aquaculture production was modified in 1999. Prefectural governors can now stop the movement of the animals listed above, infected or not, from contaminated areas and also inspect culture facilities and order the removal of contaminated animals. A negative effect of this legislation is that movement of live carp from KHV-contaminated areas is prohibited, which has caused a 50% reduction in the aquaculture production since confirmation of the disease in 2003. We do not have any legislation to stop importation of foreign aquatic animals that may be harboring other pathogens than those listed above, as long as they are apparently healthy upon importation. This may have contributed to the recent introduction of Edwardsiella ictaluri and the monogenean Neoheterobothrium hirame from abroad that now infect both cultured and wild fish.
National Shellfisheries Association: Priorities and Perspectives from the Shellfish Side
Aquatic Diagnostic Laboratory, Roger Williams University, One Old Ferry Road, Bristol, RI 02809, USA, email@example.com
The National Shellfisheries Association (NSA) is an international organization of scientists, management officials and members of industry. The focus of the organization is biology, ecology, production, economics and management of shellfish resources - clams, oysters, mussels, scallops, snails, shrimp, lobsters, crabs, among many other species of commercial importance. The NSA’s goals are: to encourage research on molluscs, crustaceans, and associated organisms with an emphasis on species of economic importance known as “shellfish”; to gather and disseminate scientific and technical information on shellfish; to promote and advance shellfisheries research and the application of results to the shellfish industry. There are currently 608 paid members. While a majority of the NSA members are from the U.S., Canada and Mexico, the NSA is an international association with total membership representing 40 countries from around the world. Membership is open to all individuals who actively support the objectives and purposes of the NSA. The organization provides an important method of communication between its members that include the regulators and aquaculturists, as well as researchers. An annual meeting is held each year that promotes these important interactions.
Primary threats to the health of both wild and aquacultured shellfish are diseases caused by protozoans, viruses and bacteria. For example, the eastern oyster (Crassostrea virginica) suffers from disease caused by a dinoflagellate-like organism, Perkinsus marinus, also called Dermo. This disease is responsible for the significant morbidity and mortality of the eastern oyster stocks along the eastern and gulf coasts of the United States. Much research into understanding how Dermo both, infects oysters and establishes disease, has been conducted. Development of resistant eastern oyster strains and management methods for diseased populations are being addressed by researchers, regulators and culturists.
Disease affects other shellfish populations, both wild and cultured, throughout the world. For example, European oysters cultured in France and England are currently suffering significant mortality due to a Herpes virus infection. Abalone on the west coast of the U.S. have seen significant reductions of wild and cultured populations by a Rickettsial-caused wasting disease. Bacteria such as Roseovarius crassostrea and Vibrio tapetis, both cause significant morbidity and mortality in juvenile C. virginica along the eastern U.S. and adult manila clams (Tapes philippinarum) along the coast of France, respectively.
The eastern U.S. coastal states are faced with the loss of significant numbers of wild oysters due to disease and overfishing. As a result other important issues related to population loss require attention. These include the development of effective methods for the repopulation of depleted shellfish stocks in the wild and identification of other types of shellfish that might be appropriate for culture.
Finally, shellfish fisheries and aquaculture must produce a good quality food product. Proliferation and accumulation of Vibrio spp. pathogenic for humans and other mammals, in the tissues of bivalves has become problematic for both fished and cultured bivalves. Methods of detecting pathogenic Vibrio spp. and management of both cultured and wild stocks in areas with high levels of pathogenic bacteria in the water is of public safety and economic concern to both regulators and culturists.
Viral Hemorrhagic Septicemia Virus: An Old Virus With New Tricks
USGS Western Fisheries Research Center, 6505 NE 65th St., Seattle, WA 98115, USA
Viral hemorrhagic septicemia virus (VHSV) is the causative agent of the fish disease known as viral hemorrhagic septicemia (VHS). This was first described as a disease of freshwater-reared rainbow trout in Europe in 1938, and it has continued to cause severe losses in the European trout farming industry since the 1950s (Wolf, 1988; Smail, 1999, Skall et al., 2005). The virus causes acute systemic disease and hemorrhagic lesions among juvenile rainbow trout with mortality rates as high as 90%. Until the late 1980s, VHSV was thought to be geographically limited to continental Europe. In 1988 VHSV was isolated for the first time in western North America from asymptomatic adult Coho salmon and Pacific cod showing extensive hemorrhagic lesions (reviewed in Meyers and Winton, 1995). Surveys of wild fish in the North-east Pacific showed an extensive reservoir of VHSV in many marine species. Although experimental challenge studies indicated the Pacific Ocean VHSV was not virulent for rainbow trout, the virus is not apathogenic as several VHS epidemics have been documented in wild Pacific herring and sardines (Meyers & Winton, 1995; Hedrick et al., 2003). Subsequently, marine fish surveys in waters around Europe found an extensive marine reservoir of VHSV, again involving many host species (Skall et al., 2005). VHSV has also been isolated from wild and farmed olive flounder (Paralichthys olivaceus) in Japan and Korea (Nishizawa et al., 2002; Kim et al., 2003). Thus, until 2005 our understanding of VHSV was that it was a marine virus with a broad host range, endemic to many marine host species in the North Atlantic and Pacific Oceans. The historical role was thought to be due to adaptation of an ancestral marine virus to cultured rainbow trout in Europe, where it has been endemic and epidemic for many decades.
VHSV has recently emerged in the Great Lakes region of North America. This represents a geographic invasion of an extensive ecosystem, and it is the first time VHSV has caused large-scale epidemics in free-ranging freshwater fish populations. The emergence of VHS in the Great Lakes began with the isolation of VHSV from a diseased muskellunge (Esox masquinongy) from Lake St. Claire in 2003 (Elsayed et al., 2006), and a large-scale fish kill in freshwater drum (Aplodinotus grunniens) in Lake Ontario in 2005 (Lumsden et al., 2007). In 2006 and 2007 there were numerous large fish kills throughout the lower Great Lakes, often involving multiple host species. VHSV has now been isolated from 28 Great Lakes host species from a wide diversity of taxonomic families, including several important aquaculture and recreational species such as muskellunge, walleye, Chinook salmon, and whitefish. Geographically it has spread into Lake Huron, Lake Michigan, and several inland lakes and waterways of New York, Ohio, Michigan, and Wisconsin. Most disturbingly, it has been isolated recently in the Ohio River watershed, which is not within the Great Lakes basin but instead drains into the Mississippi River. In 2008-2010 there have been fewer reported fish kills due to VHSV in the Great Lakes, but several surveillance studies found VHSV frequently in both fish and water samples from numerous sites, indicating the virus persists (Bain et al., 2010). To date, Great Lakes VHSV has spread to all five of the major Great Lakes, but it has been isolated only from free ranging fish, and it has not been found in aquaculture.
VHSV is a member of the genus Novirhabdovirus, within the family Rhabdoviridae (Tordo et al., 2004). The genome of VHSV is a linear single-stranded, negative-sense RNA molecule of approximately 11,000 nucleotides, with six genes in the order 3’-N-P-M-G-NV-L-5’ (Schüetze et al., 1999). Extensive genetic typing of hundreds of VHSV field isolates has revealed divergence into phylogenetic sub-groups. Prior to the emergence of VHSV in the Great Lakes, phylogenies of N and G gene sequences by European researchers defined four genotypes of the VHSV that appeared to be distributed geographically, rather than by host or year of isolation (Snow et al., 2004; Einer-Jensen et al., 2004). Genotypes I, II and III are found in marine fish in waters around Europe, and within genotype I, all VHSV isolates from European freshwater trout farms fall into a sub-lineage called Ia. VHSV genotype IV contains all VHSV isolates from the Pacific coast of North America, as well as VHSV from Japan and Korea. When VHSV emerged in the Great Lakes, the first isolate obtained (strain MI03 from Michigan in 2003) was typed by its glycoprotein gene sequence as being most closely related to the North American VHSV genotype IV, and was clearly distinct from the three European genotypes (Elsayed et al., 2006). Although MI03 was closest to genotype IV, it differed from the closely related Pacific coast genotype IV isolates by 3.6–3.7% at the nucleotide level. Therefore the Great Lakes isolate was placed in a distinct sub-lineage (IVb) of the phylogenetic tree, with the Pacific coast VHSV isolates comprising sub-lineage IVa (Elsayed et al., 2006). Four VHSV isolates from fish in brackish water off the Atlantic coast of Canada have also been characterized and found to be within major genotype IV, closely related to Great Lakes VHSV (Gagne et al., 2007).
The phylogenies of VHSV revealed evidence of adaptation to cultured rainbow trout in the past, followed by long-term persistence and economic losses in European trout aquaculture. It appears that an ancestral virus from genotype I in marine hosts gained entry to cultured trout and diverged into the prevalent sub-lineage Ia that has plagued European trout farms since the 1950s (Einer-Jensen, 2004). This host jump into rainbow trout is hypothesized to have resulted from use of unpasteurized fish by-products as feed for juvenile fish in the early years of fish culture. The potential for VHSV to adapt to cultured trout has been confirmed more recently by VHS outbreaks in marine netpen-reared rainbow trout in Europe. Outbreaks in Sweden and Finland between 1998-2002 were found to be caused by genotype I subtypes Ia and Ib. In the most recent case in Norway (Lyngstad et al., 2008) the disease epidemic diagnostic signs were typical for VHSV genotype Ia, but genetic typing revealed that it was caused by a virus from genotype III. This is the first time a genotype III virus has been isolated from cultured trout. These adaptation events are not numerous considering the number of years fish have been cultured, but their consequences can be great, imposing genuine limitations on trout aquaculture. Extensive experimental infection studies with European VHSV isolates from genotypes I, II, and III have shown that marine isolates are not virulent for rainbow trout (Skall et al., 2005), but they can be for marine species such as turbot. VHSV outbreaks have been reported in cultured turbot in both Scotland and Japan, suggesting that the presence of the marine reservoir of VHSV can be a threat to the culture of this species.
At present, experimental infection studies show that the new VHSV genotype IVb that is emerging in the Great Lakes region is not currently virulent for rainbow trout, but it has an extremely broad host range, and is virulent in Great Lakes species such as yellow perch. Lessons from Europe indicate that it has the potential to adapt to cultured hosts. Since the initial detection of VHSV in the Great Lakes numerous state, federal, and academic fish health researchers have contributed great effort toward investigating fish kills and surveying for the virus in Great Lakes fish. This has resulted in over 100 isolations of VHSV from various fish species at a wide range of locations and at different times. Genetic typing indicates that the genetic diversity of VHSV in the Great Lakes is extremely low at this early stage in the emergence event, but there are indications of the beginning of diversification. Genetic typing has identified 12 different genotypes of Great Lakes VHSV by sequencing of a 669-nucleotide portion of the viral G gene. These genotypes appear randomly distributed among hosts and over time, but there is evidence of early spatial patterns for the most common types. The emergence of VHSV IVb in the Great Lakes represents the first time this virus has become established in a freshwater ecosystem in North America. The large-scale epidemics that have ensued in free-ranging fish are typical of the interactions between a newly introduced pathogen and naive host populations that have no prior experience with the pathogen, and thus no immunity.
In nature, VHSV is transmitted both horizontally by water-borne virus, and vertically as egg-associated virus (Wolf 1988; Smail, 1999). In salmonid aquaculture, vertical transmission can be eliminated by egg disinfection with iodophore compounds. Despite decades of effort, there are no commercially available vaccines in common use against these pathogens. Inactivated, attenuated, and sub-unit vaccines can be effective, but have not proven sufficiently consistent or safe for common application. DNA vaccines work well (Lorenzen and LaPatra, 2005) but are not currently licensed in the U.S. or Europe, and at present require injection delivery, limiting their use in juvenile fish. Thus the principle methods of controlling VHSV remain destruction of infected fish and strict biosecurity measures to prevent introduction of the pathogen to aquaculture facilities. From a research perspective, the most promising developments for enhancing our knowledge of both European and North American VHSV include many advances in fish immunology, and the generation of infectious clones of VHSV. Combined with studies of viral infections both in vivo and in vitro, these tools will provide the next generation of tricks on the human side, for dealing with the tricks of this adaptable virus.
Bain M.B., Cornwell E.R., Hope K.M., Eckerlin G.E., Casey R.N., Groocock G.H., Getchell R.G., Bowser P.R., Winton J.R., Batts W.N., Cangelosi A., Casey J.W. (2010). Distribution of an invasive aquatic pathogen (Viral hemorrhagic septicemia virus) in the Great Lakes and its relationship to shipping. PLoS one 5(4):1-8.
Einer-Jensen K., Ahrens P., Forsberg R. & Lorenzen N. (2004) Evolution of the fish rhabdovirus viral haemorrhagic septicaemia virus. Journal of General Virology 85, 1167-1179.
Elsayed, E., Faisal, M., Thomas, M., Whelan, G., Batts, W., & Winton, J. (2006). Isolation of viral haemorrhagic septiceaemia virus from muskellunge, Esox masquinongy (Mitchill), in Lake St Clair, Michigan, USA reveals a new sublineage of the North American genotype. Journal of Fish Diseases 29, 611-619.
Gagne N., MacKinnon A.-M., Boston L., Souter B., Cook-Versloot M., Griffiths S., and Olivier, G. (2007) Isolation of viral hemorrhagic septicemia virus (VHSV) from mummichogs, sticklebacks, striped bass, and brown trout in eastern Canada. Journal of Fish Diseases 30:213-233.
Hedrick, R.P., Batts, W.N., Yun, S., Traxler, G. S., Kaufman, J., & Winton, J.R. (2003). Host and geographic range extensions of the North American strain of viral hemorrhagic septicemia virus. Diseases of Aquatic Organisms 55, 211-220.
Kurath, G. (2008). Biotechnology and DNA vaccines for aquatic animals. Review, Scientific and Technical Office of International Epizootics 27, 175-196.
Lorenzen N. & LaPatra S. E. (2005). - DNA vaccines for aquacultured fish. Revue Scientifique Et Technique-Office International Des Epizooties 24, 201-213.
Lumsden J.S., Morrison B., Yason C., Russell S., Young K., Yazdanpanah A., Huber P., Al-Hussinee L., stone D., and Way K. (2007). Mortality event in freshwater drum (Aplodinotus grunniens) from Lake Ontario, Canada, associated with viral hemorrhagic septicemia virus , Type IV. Dis. Aquat. Org. 76:99-111.
Lyngstad, T.M., Hogasen, H.R., Orpetveit, I., Hellburg, H., Dale, O.B., & Lillehaug, A. (2008). National Veterinary Institute's report series No. 3. Scientific evaluation of the eradication of viral hemorrhagic septicemia in Storfjorden. National Veterinary Institute, Oslo, Norway.
Meyers T.R. & Winton, J.R. (1995). Viral hemorrhagic septicemia virus in North America. Annual Review of Fish Diseases 5, 3-24.
Nishizawa T., Iida H., Takano R., Isshiki T., Nakajima K., and Muroga K. (2002). Genetic relatedness among Japanese, American, and European isolates of viral hemorrhagic septicemia virus (VHSV) based on partial G and P genes. Dis. Aquat. Org. 48:143-148.
Schütze, H., Mundt, M., & Mettenleiter, T.C. (1999). Complete genomic sequence of viral hemorrhagic septicemia virus, a fish rhabdovirus. Virus Genes 19, 59-65.
Skall, H.F., Olesen. N.J., & Mellergaard, S. (2005). Viral haemorrhagic septicaemia virus in marine fish and its implications for fish farming -- a review. Journal of Fish Diseases 28, 509-29.
Smail, D.A. (1999). Viral Haemorrhagic Septicaemia. Pages 123-146 In Fish Diseases and Disorders, Volume 3, Viral, bacterial, and fungal infections. P.T.K. Woo & D. W. Bruno, eds. CAB International, New York.
Snow M., Bain N., Black J., Taupin V., Cunningham C.O., King J.A., Skall H.F., & Raynard R.S. (2004). Genetic population structure of marine viral haemorrhagic septicaemia virus (VHSV). Diseases of Aquatic Organisms 61, 11–21.
Tordo, N., Benmansour, A., Calisher, C., Dietzgen, R.G., Fang, R-X, Jackson, A.O., Kurath, G., Nadin-Davis, S., Tesh, R.B., & Walker, P. (2004). Family Rhabdoviridae, In "The eighth report of the international committee for taxonomy of viruses". Academic Press, San Diego.
Wolf, K. (1988). Infectious hematopoietic necrosis virus. Pages 83-114 in Fish Viruses and Fish Viral Diseases. Cornell University Press, Ithaca, New York.
Status of Finfish Culture and Parasitic Diseases in China
State Key Laboratory of Biocontrol and School of Life Sciences, Sun Yat-sen University, 135 West Xingang Rd, Guangzhou, 510275 China firstname.lastname@example.org
Historical records of fish culture and parasitic diseases
Finfish culture has a very long history in China, as common carp were raised for food in freshwater ponds as early as 1,000 years BC. The fish parasites and their detrimental effects were were paid attention to by ancient fish farmers, as recorded in the book “Jottings of Interrelationship of Things” written by Shushi, a writer in the Song Dynasty (960 – 1279). Sushi noted that the white spot on fish, called lice, could be eliminated by casting the balk of willow. Although the parasite referred to was probably not what we would refer to as lice today, we can however deduce that the ancient fish farmers had realized the impact of fish parasites, and tried to prevent and treat them. Subsequently, Xu GuangQi in the Ming Dynasty (1368 – 1644), wrote in his book “Nongzheng Quanshu (Agricultural Pandect)”, that poor conditions in the fish pond resulted in infection with lice, which are as round and as big as a soybean (Zhang et al, 1999).
Present status of water resources and aquaculture
The total inland water area in China is about 17,600,000 hectares, and of this about 5,642,000 hectares (approximately one third) can be used for aquaculture. The total area of coastal seawater in China is similar to that of freshwater, and the area suitable for mariculture before 2001 was some 1,330,000 hectares (Lu, 2001). In 2007, the total area of water in China that supports aquaculture was actually 5,633,210 hectares, 4,301,000 hectares of which were freshwater, and 1,331,000 hectares of which were for mariculture (Kuan, 2008).
Overview of Chinese fisheries
A remarkable development in fisheries in China has happened in the past 60 years. In 1949, the total annual fishery catch was only 524,000 metric tons, and within 30 years (1978) the catch reached 5,366,100 metric tons, ten times that in 1949. In the last two decades, due to the country’s economic opening to the world, and the adjustment of the structure of fisheries, the total annual fishery production in China rose ten times again, to its 2008 value of 48,956,000 metric tons (Zhou & Li, 2009).
When separately considering the developments of the Chinese capture fishery and aquaculture, we can easily see the importance of the adjustment of the structure in the fishery industry. In 1978, the tonnage of the capture fishery (freshwater and marine) was 3,817,200 tons, accounting for 71.14% of total fishery catch. In 2008, the tonnage of the total capture fishery was 13,744,600 tons (a more than 3 fold increase in only 10 years), yet this then comprised only 28.1% of the total annual fishery production in China, showing the dramatic rise of the importance of aquaculture.
In the course of the rapid development of China’s fisheries, some landmarks are particularly noticeable, (i) in 1989, the production from mariculture reached 2,757,300 tons, and ranked first in the world for the first time, (ii) in 1990, total fishery production was 14,272,600 tons, and ranked first in the world, (iii) this first position has been held for 20 years (Zhou & Li, 2009; Li & Wu, 2009), and (iv) as a result, the per capita annual consumption of aquatic products reached 36 kg, 1.6 times the world average (Li & Wu, 2009).
In addition to meeting domestic demand for aquatic products, Chinese fishery products were also exported to other countries, as reflected in following statistics. In 1978, the value of exported fishery products was 260 million US dollars. In 2008, the value had increased to 10.6 billion US dollars. For each year since 2002, China has been the world leader in tonnages and value of exported fishery products. These products accounted for around 30% of the export value of total agricultural products in China (31 billion US dollars in 2007) (Li & Wu, 2009).
Finfish culture in China
The finfish culture environments in China are highly diverse, because of the high diversity of topographic conditions and water environments; from tropical warm water in the south of the country, to the cold water in the north of the country; from freshwater rivers and ponds, to brackish lakes, ponds and estuary water, to stable sea water sites far from the coast which are now gradually used for large scale net culture.
In China, the fish culture systems include water-based systems, such as cages and pens, both inshore and off-shore; land-based systems such as rain-fed ponds; irrigated or flow-through systems, tanks and raceways; land/water-based systems, such as sea ranching; recycling systems such as high control enclosed systems, more open pond-based recirculation; monoculture and polyculture systems; integrated farming systems, such as livestock-fish, agriculture-aquaculture such as rice field culture of fishes.
Stocking densities in fish culture facilites range from extensive such as fish cultured in a lake, to semi-intensive in the ponds, and intensive culture in the net cages, and indoor industrial fish culture. Polyculture of species of different ecological niches has been very common, such as the mixture of Cyprinus carpio, Mylopharyngodon piceus, Hypophthalmichthys molitrix and Ctenopharyngodon idell in the freshwater ponds, and Trachinotus ovatus, Scylla serrata and Penaeus monodon (sometimes with Gracilaria confervoides) in marine culture ponds, which are commonly considered very effective for maintaining the healthy water quality and preventing diseases.
There are more than 60 species of freshwater fishes cultured for food in China. The four traditionally cultured freshwater fishes, known as “the four fishes for everybody”, are black carp, Mylopharyngodon piceus, grass carp, Ctenopharyngodon idella, silver carp, Hypophthalmichthys molitrix and big head, Aristichthys nobilis (all are cyprinids and native species). Besides these species, common carp, Cyprinus carpio, crucian carp Carassius auratus, bream Parabramis pekinensis, and dace Cirrhinus molitorella (native cyprinids) are also very common. With the development of freshwater culture, more and more fish species, such as Tilapia, Tilapia mossambica (Cichnidae), and large mouth bass, Microptenus salmoides (Centrarchidae), have been exploited or introduced for culture.
There are now more than 70 species of marine fish cultured for food in China. Growth of mariculture in China has experienced several stages. From the 1950s to the 1960s, poor economic conditions meant that culture was concentrated on herbivorous species, such as grey mulluts Mugil cephalus, and redeye mullet, Liza haematocheila (Mugilidae), and milk fish, Chanos chanos (Chanidae), which were farmed extensively in naturally recycling coastal ponds. From the 1970s to the end of the 1990s, such extensive marine culture gradually shrank, as most farms were redeveloped as shrimp ponds, due to the distinctly higher profits. Meanwhile, new techniques in marine fish culture were developed. In the northern part of China, where it is cold in winter and temperature control is difficult, intensive industrialized indoor farming systems were developed, resulting in successful industrial culture of the Olive flounder (bastard halibut), Paralichthys olivaceus, and a species imported from England in 1992, the pygmy flounder, Tarphops oligolepis (Bothidae). In the southern part of China, the culture of marine finfishes in offshore floating cages was developed, because of the good water exchange and advantage of higher temperatures. Since the beginning of 21st century, a rational plan of coastal resource management and disease prevention has been included in the programming of mariculture as a whole. For example, large, submersible net cages have been developed, and put into practice, by some big mariculture corporations in order to prevent the deterioration of the nearshore marine environment and destructive accidents caused by storm tides.
Government efforts to support aquaculture
Central to the growth of aquaculture in China was significant government investment, and the conscientious efforts of scientists and the fish farmers. In 1950’s there was only one research lab and several extension stations for aquaculture technologies in the coastal provinces. Subsequently, the government established three fishery institutes (Yellow Sea, East China Sea and South China Sea), two institutes of oceanography belonging to the academy of sinica (Institute of Oceanography in Qingdao, and South China Sea Institute of Oceanography in Guangzhou) and three fisheries institutes for the major rivers (Yangze River, Pearl River and Heilongjiang River), and every districts or county had its own institute of fisheries or aquaculture. By 1987, there were 107 fishery research institutes with 6,700 scientists and staff doing research on fisheries or aquaculture. By 2008, there were 13,217 stations established for extending fishery and aquaculture techniques. Most of the institutes were fully sponsored by the central government (9,085), some were partially sponsored by the central government (2,809), and the remainders were privately funded. In 2008, there were a total of 36,887 people working in these extension stations (Zhou & Li, 2009).
Realizing the limits of the natural fishery resources, and the importance of sustainable exploitation of fishery resources, China started the changes from a predominantly capture fishery to predominantly culture fishery in 1980s, and the total production of aquaculture exceeded that of the capture fishery for the first time in 1988 (Zhou & Li, 2009). A fishing ban policy (for two months each year, and the times are slightly different in the different parts of coast according to the reproduction periods of main fishes) along the coast of China has been implemented for more than ten years since 1999. Besides restraining the capture fishery, the government entrusted some institutes to release seedlings of fishes into the river and seas to increase the natural resource, with the numbers released exceeding over 100,000,000 per year and attained 19.7 billion in 2008 (Li, 2009).
Important parasitic pathogens in aquaculture in China
Although more than 90 species of parasites have been reported as pathogens causing diseases of freshwater fishes, only around 30 species of them were frequently found from the 26 species of fishes most commonly cultured on a large scale. Until 2008, a total of 28 kinds of parasitic diseases of fishes (freshwater and marine fishes) were included on the list of aquaculture pathogens for national surveillance (internal data).
Based on the investigation on the parasites and parasitic diseases of largely cultured freshwater fishes in 2008 (Li & Wang, 2009), five kinds of parasitic diseases were listed and emphasized, they are Myxosporidiosis caused by a large groupe of pathogens in the class of Myxosporidea such as Sphaerospora branchialis, Myxosoma sinensis, Myxobolus drjagini, and Henneguya weishanensis; trichodiniasis resulted from infections of about 10 species of Trichodina such as T. nobilis; dactylogyrosis with the notorious pathogens including Dactylogyrus vastator, D. vaginulatus and D. lamellatus; sinergasilosis caused by several species of pathogens such as Sinergasilus major and S. polycolpus and lernaeosis resulted from the infection of several species of Lernaea (Zhang J.Y. et al. 1999). While for the maricultured fishes, the ciliate Cryptocaryon spp. and the monogenean Neobenedenia epinephelus, and are the most notorious, and frequently cause trouble to many species of cultured marine fishes.
Impact of current and emerging parasite diseases on finfish culture
Outbreaks of disease in aquaculture is the main factor restraining production of high quality aquatic products. Parasites are very dangerous to hosts in confined environments such as the cultured pan and densely-stocked ponds.
Although it is hard to estimate the economic losses associated with outbreaks of parasite diseases for the whole country, the following records of mortality, and statistics of local economic losses, reflect the severity of the problem. The notorious cases that have been reported include: 1) in 1960, the Xihu fish farm in Wuhan suffered 90% mortality of cultured fishes (several species of cyprinids, no indication of details) due to diplostomiasis; 2) in 1985, there were numerous deaths of silver carp, Hypophthalmichthys molitrix in the Yingshou reservior due to severe infection with the monogenean Dactylogyrus vaginulatus; 3) in 1991, the loss of nearly 100,000 kg of netcage cultured carp in the Changshou, Sichuan Province resulted from heavy infection with the tapeworm Bothriocephalus infection; 4) in 1991, nearly all fishes (no indication of species name in the literature) held in pens in Daihai lake, Inner Mongolia, died in 40 days due to diplostomiasis; and 5) in 1992 Raoping country, Guangzhou province, suffered an economic loss of about 1,400,000 US Dollars due to the outbreak of the crustacean Argulus on maricultured groupers Epinephelus spp. (Zhu, 2007).
Based on historical reports, Guo et al. (1995) estimated that annual mortality of fishes resulting from fish parasites was between the low of 20 to 30% and the high of 90% in the fish farms in China, particularly in the southern provinces.
Within the last decade, the parasite problems in finfish aquaculture have included the following: 1) in September 2001, many species of marine fishes including red seabream Pagrosomus major, sea perch Lateolabrax japonicus, large yellow croaker Larimichthys crocea and red drum Sciaenops ocellatus in about 4,000 marine net cages suffered an outbreak of Cryptocaryon irritans, with 20-30% mortality (Lin, 2002); 2) in 2004, the total economic loss of aquaculture caused by diseases was about 15,000,000 US Dollars in Hunan Province, nearly 1/3 of which was directly caused by parasitic diseases (Zhu, 2007); and 3) in 2005, among 5,000 broodstock of the paddlefish Polyodon spathula, 600 died due to serious arguliosis (Zhang, 2005).
Management: practices and infrastructure affecting fish health
The management and control of parasitic diseases in aquaculture in China generally include pretreatment of culture facilities, quarantine, scientific management of aquaculture systems, surveillance of diseases, chemical treatments of diseased fish, use of Chinese herbal medicines, and ecological approaches to prevention of parasite infections.
Pretreatment of aquaculture facilities is frequently used in fish culture. In pond culture of freshwater fishes, lime at a dose of 1,500 to 2,500 kg/per hectare of bottom area, is widely used for the treatment of dried ponds. Liao & Shi (1956) proposed that application of raw lime prior to stocking, can kill intermediates hosts which harbor cestode procercoids, and the application of this treatment has finally led to the eradication of Bothriocephalosis in cultured grass carps. In mariculture, it is strongly recommended that net pens or cages are periodically treated by chemicals or exposure to sunlight to remove the attached organisms, and to kill pathogens such as monogenean eggs (Wang et al. 2002).
Treatment of fingerlings, prior to stocking is also of significance for safeguarding stock. Generally fingerlings of freshwater fishes are bathed in a potassium permanganate solution, 200mg/L for 30 minutes, which can kill most ectoparasites (Liu & Yu, 2006). For the treatment of seedlings of marine fishes prior to stocking, a variety of baths are used to kill ectoparasitic protozoans and monogeneans, including a freshwater bath for 5 to 10 minutes, a 15 to 20 minute bath in copper sulfate solution (10 mg/L), and a 5 – 10 minute bath in a glutaraldehyde solution (20 to 30 mg/L) (Lin & Huang, 2007). Moreover, hatchery and fish seedling farms are required to have quarantine inspection facilities, to minimize the disease transmission between farms.
Scientific management of culture systems and monitoring of pathogens are also critical for disease prevention in cultured fishes. The central government has been trying to help the farmers by predicting the outbreaks of diseases, and by training technicians in disease treatment via investment in relevant research projects at specified institutes. In 2008, the National Fisheries Technology Extension Center (NFTEC) received 34,171 sets of data about the disease occurrence of 4,643 farms via 2,703 monitoring stations covering an area of about 265,200 hectares, which accounts for 8.35% of the total aquaculture area in China.
In spite of the many prophylactic measures that are applied, medical treatments are still the main approach for parasitic diseases of fish, due to the inevitably high intensity production of the fish and the economic effectiveness of the medical treatments. Commonly used chemicals include trichlorphon, quicklime, copper sulfate, potassium permanganate, formalin, and many other chemicals. For freshwater fishes, saline baths are frequently used to treat fish with ectoparasites. For marine fish with ectoparasitic infections, particularly monogeneans, fish farmers generally treat the fish by routine freshwater baths about every two weeks, which is very effective for decreasing the parasite burden, although it is difficult to eradicate the pathogen, and sometimes the fish are injured due to rubbing each other in a limited container during treatment.
Chinese medicinal herbs have a long history of use in aquaculture. They have been added to the food as an attractant, immune stimulant, and for killing parasites; they are widely considered non-toxic, residue-free, and do not raise concerns about drug resistance (Ma & Li, 2010).
The practice of polyculture, and stocking at suitable densities, are very important for disease control and environmental sustainability. The combination of species is generally made according to the ecological complementarities of the species, and the ponds and water conditions. As an ecological approach to decreasing infection with the crustacean Lernaea on cultured fishes, Hu & Wen (2009) reported that adding 750-900 individuals of yellow headed catfish Pseudobagrus fulvidraco per hectare can effectively stop the outbreaks because P. fulcidraco can feed on Learnaea spp..
Introduced fish and introduced parasites
Global exchange and species introductions in aquculture have become very frequent. To date, there are some 35 species of fish introduced from over the world, that are now cultured in China. In some areas, the introduced species, such as tilapia, Oreochromis spp. and red drum, Sciaenops ocellatus, have become the dominant species, and are now in large scale culture. Their native parasites have been observed in China, such as the monogenea Cichlidogyrus sclerosus and Scutogyrus longicornis from gills of a hybrid tilapia of Orechromis aureus (S.) ♂ and Orechromis niloticus (Wu et al., 2006). The influence of both native parasites, and the novel parasites introduced with the introduced host fishes, on the local parasite fauna are worthy of thorough investigation and evaluation, to support the sustainable culture and protection of locally relevant species of fishes.
Fish parasites of public health importance
Not only are parasites of importance for fish health, but some are also of concern for public health. In freshwater fishes, the trematode Clonorchis sinensis is notorious for causing the human disease of clonorchiosis or fascioliasis. This is an important trematode in the biliary passages and occasionally the pancreatic duct, of humans and fish-eating mammals of the Orient, chiefly Japan, Korea, China and Indo-China (Lun et al, 2005). Many species of freshwater fishes can be infected by the cercaria of this trematode. Humans become infected by eating raw or undercooked fish such as sashimi, fish porridge, where the metacercaria of trematodes are found. There are 22 of 34 provinces in China where this disease occurs, and it is estimated that the total number of infected people in China is about 16,480,000. Clonorchiosis can cause severe liver damage, and 60% of the patients have the diagnostic symptom of hepatomegaly and mild pressing pain.
Among the parasites of marine fishes, Anisakis spp. is the group of nematodes with the greatest potential for human infection. They use fish as intermediate hosts, and warm-blooded marine mammals such as seals, whales and dolphins, as normal definitive hosts (Yuan & Zhang, 2007). Humans become infected by eating raw or undercooked fishes or other marine products, infected with anisakis larvae. This is a global zoonotic parasitic disease. To date, more than 30,000 cases of human infection have been reported from over 27 countries (Xu X. et al, 2009). In China, 177 species of marine fishes from different seas have been investigated for anisakis larval infection, and 151 species were found to infected (86.46%), and the average prevalence of infection in these susceptible fishes was 47.1% (1,861 of 3,951 individuals investigated). Because of the high prevalence of anisakis larva in marine fish, and the common practice of eating sashimi, anisakiasis has received a great deal of concern from the government.
Conclusions and future outlook
Parasitic pathogens of cultured fishes are numerous and have caused huge economic losses in China. However, our knowledge about these pathogens is still very fragmented. Therefore, forcasting techniques based on the life cycle and epidemiology of the pathogens, and simple, precise and rapid dignostic techniques, are important tasks for scientists.
Innovative culture models, and the standardization of previously proved models, both need further study and tests, particularly those such as rational polyculture technique and rice field fish culture that can prevent or reduce fish disease. Because increasing numbers of fish species are brought into aquaculture, rigorous studies on their parasites under culture conditions are needed in order to maintain healthy stock. Furthermore, it is also necessary to evaluate the pathogenic parasites and the host-parasite relationships in newly developed or selected strains, and in genetically modified fish in culture. For parasites of public health concern, publicity and education for the fish derived human parasitic diseases should be paid more attention to, in order to prevent or reduce the human infection of fish parasites.
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Novel Discoveries on the Immune System of Teleost Fish, and Their Impact Into the Future Development of Mucosal Vaccines
J. Oriol Sunyer*
Department of Pathobiology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, 19104 email@example.com
1. RATIONALE AND
1. RATIONALE AND
Aquaculture is the fastest growing animal food sector in the United States, as well as in the global marketplace. Disease and health management problems are known to be one of the major hurdles for the developing aquaculture industry in the US and worldwide. Therefore, such deficiencies in health management could prevent the continued development of the industry. Clearly, prevention and spread of infectious diseases are still largely unresolved issues; this is primarily due to our lack of basic knowledge of many aspects of the immune system in fish. One of the areas that require further attention is our understanding of the immune mechanisms that lead to the recognition and clearing of microbes, as well as the molecular processes involved in the uptake and processing of antigens. Better knowledge in this area is fundamental to the development of new and improved therapeutic tools, including immunostimulants, as well as new strategies for antigen delivery and fish immunization.
For the last five years our group has focused on two new areas that involve the study of fish B lymphocytes and their roles in innate and adaptive immune responses. Such studies have recently yielded several major findings, including the discovery of phagocytic B cells in fish, the characterization of a novel teleost fish B cell lineage in uniquely expressing IgT, and the finding that fish IgT is an immunoglobulin specialized in mucosal immunity (see below).
2. DISCOVERY OF PHAGOCYTIC B LYMPHOCYTES IN FISH
2.1 Phagocytic cells of mammals and fish: Phagocytosis, the engulfment of large particles (>0.5 mm) by immune cells, plays an essential role in the uptake and destruction of microbes as well as in the initiation and development of adaptive immune responses (1, 2) . It begins through interaction of opsonized or non-opsonized particles with phagocyte receptors (e.g. scavenger, Toll-like, Fc, complement receptors), and requires actin polymerization. Following internalization, microbes are destroyed through the action of potent innate immune mechanisms. Subsequently, degraded microbial antigens can be processed by antigen presenting cells (APC) and presented to T cells, effectively initiating adaptive immunity mechanisms (1) .
In higher vertebrate species such as mammals, phagocytosis is primarily carried out by professional phagocytes, cells of myeloid origin that include polymorphonuclear cells (PMNs), monocytes and macrophages (3) . In lower vertebrate species such as teleost fish, phagocytes are known to be morphologically, functionally and structurally very similar to those of higher vertebrates. Thus, up until recently granulocytes and macrophages were also thought to be the main phagocytic cells in these species (4, 5) .
2.2 B cells of fish: Until very recently, the little knowledge we had from fish B lymphocytes pointed to the notion that these cells were essentially restricted to adaptive immunity (5) and that they resembled mammalian B-1 B cells, that is, they expressed membrane IgM as a monomer and secreted soluble IgM as a polymer (6, 7) . However, we have recently unearthed the existence of a novel B cell lineage in fish that uniquely expresses surface IgT (8) , a teleost immunoglobulin that was identified 5 years ago (9) . Moreover, it appears that catfish contain a B cell subset that expresses only IgD (10) , thus suggesting the existence of at least three different B cell subsets in teleosts.
We have recently shown that IgM+ B cells of teleosts are the prevalent B cell subset in blood, spleen, head kidney and peritoneal cavity. In contrast, the IgT+ B cell subset is predominantly found in the gut of fish (8) . One striking difference between B cells of teleost fish and mammals is their abundance in blood. Thus, we and others have reported that B cells in several teleosts represent an average of ~50-60% of all peripheral blood leukocytes (PBLs), whereas monocytes and neutrophils combined represent only ~10-20% of PBLs (11-14) . In contrast, the percentage of B cells in human PBLs is only 2-8%, whereas the percentage of neutrophils/monocytes is ~50-70 % (15) . In addition, when looking at cell count data, our results routinely indicate that the IgM+ cell count in trout is 5000-10000 per ml blood (data not shown), whereas in humans, the B cell count ranges ~150-720 per ml of blood (16) . Hence, it is clear that both the percentage and number of B cells in fish are several fold higher than that of humans, whereas the percentage of neutrophil/monocytes is significantly lower in fish when compared to humans.
2.3 B lymphocytes are active phagocytes in teleost fish: Up until recently, the dogma dictated that normal cells of lymphoid origin (i.e., B cells, T cells) were not able to perform phagocytosis (3) . Contrary to this belief, recent studies in our laboratory have shown that large subsets of trout IgM+ B cells are capable of efficient phagocytosis (11) . In contrast T-cells and thrombocytes were devoid of such capacity. Importantly, the phagocytic ability of trout IgM+ B cells was enhanced by opsonization of bacteria with trout complement or IgM. After particle internalization, trout IgM+ B cells were found to initiate degradative pathways through phagolysosome formation. Significantly, phagocytic B cells were found to have the capacity to effectively kill internalized bacteria. We identified this phagocytic activity in the majority of IgM+ B cells from trout and catfish blood, head kidney and peritoneal cavity. This represented the first time that such phagocytic activity has been described in normal B cells from any animal species. These findings were reported in Nature Immunology (11) and made the cover of the 2006 October issue. Recent reports have confirmed our finding in other fish, thus showing the presence of phagocytic B cells in Atlantic salmon and cod (17) . Moreover, we have recently reported that the newly discovered IgT+ B cell lineage is also phagocytic and microbicidal (8) .
2.4 Significance for the area of fish health: The main role assigned up until recently to B cells in fish was the secretion of antibodies (IgM) upon antigenic stimulation. However, our new findings also point to a very important role of these cells in innate immunity; more specifically, in the phagocytosis and killing of microbes (11) . We hypothesize that the capacity of fish B cells to ingest large particles will also have an impact on adaptive immune processes such as those related with the processing and presentation of the phagocytosed antigen. Therefore this previously unanticipated and novel role of B cells in phagocytic processes is likely to fundamentally change the way we view innate and adaptive immunity in fish. From an applied perspective, this finding has important implications for the design of fish immunotherapeutics. In that regard, a significant amount of research in fish immunotherapeutics is devoted to the development of immunostimulants that can stimulate innate and/or adaptive immune mechanisms (18) . Thus, one could envision the search of substances or compounds that stimulate the phagocytic activity of fish B cells. On one hand, such substances would be likely to stimulate innate immunity by enhancing microbe uptake and killing, while on the other hand, adaptive immunity would be enhanced through increased B-cell specific processes of antigen uptake and presentation. Another area that we anticipate will greatly benefit from these findings relates to the design of fish vaccines. Since a very large percentage of fish B cells are able to ingest particles, we believe that particulate antigen-delivery systems in fish would be more effective than those based on the delivery of soluble antigens. Accordingly, one could foresee research on technologies that focus on antigen-coating of particles that have been previously shown to be avidly uptaken and phagocytosed by B cells. Thus, future research in that area may open an avenue for the development of more effective fish vaccines based on particulate antigen-delivery systems that target B cells, in addition to other known antigen presenting cells.
3. IGT, A TELEOST FISH IMMUNOGLOBULIN SPECIALIZED IN MUCOSAL IMMUNITY
3.1 Teleost fish immunoglobulins: Teleost fish species contain three different isotypes, IgM, IgD and the recently described IgT/Z (9, 19, 20) . IgM and IgD: Teleost IgM is a tetrameric molecule, as opposed to the pentameric mammalian IgM (19, 21) . In all species analyzed thus far, the tetrameric IgM is the most abundant (if not the only) immunoglobulin present in serum and other fluids, and up until recently it was thought to be the only fish antibody responding to antigenic stimulation (19, 21) . In fact all antibody responses measured and reported for all teleost fish species for the last ~30 years have been performed on the IgM isotype.
The IgM antibodies generated in teleost fish are of low affinity and limited heterogeneity, and the response time is generally longer than that in mammals (19, 21) . In this regard, detectable IgM titers are not normally seen until after the 3rd or 4th week of immunization (19, 22) . In teleost fish, IgM is secreted by plasmablasts and plasma cells (23, 24) . It has been shown that the majority of IgM-secreting cells in trout are localized in the head kidney. It is well known that after booster immunizations, teleost fish show significant increases in IgM (19, 21) . In addition to playing a key role in systemic responses, IgM has been shown to play a role in mucosal responses since the presence of antigen-specific IgM, albeit low, has been demonstrated in the skin and gut mucus of these species, including rainbow trout (22, 25, 26) .
While IgD-like molecules have been cloned in several teleost species (19, 27) , its role in fish immunity is unclear.
IgT/IgZ: Five years ago this immunoglobulin isotype was cloned in rainbow trout (9) , and zebrafish (20) . This isotype has been identified in all analyzed teleost fish, except in the catfish. However, the catfish genome is not available thus far, therefore, the possibility still exists that the catfish ortholog for IgT has not yet been found. Up until recently, the role of IgT in fish immunity was an enigma. Recently we have reported that IgT is an immunoglobulin specialized in gut mucosal immunity (8).
3.2 Structural and functional characterization of IgT: Up until recently, nothing was known about the protein structure of IgT, and its distribution and production by putative B cells. More importantly, its function was an enigma. This year we have reported the structural and functional characterization of IgT (8) . We have produced polyclonal and monoclonal antibodies against IgT that have enabled us to identify and characterize IgT from different fish body fluids. At the protein level we have shown that IgT is a monomeric immunoglobulin in serum. However in the gut mucus, IgT is chiefly polymeric and is more abundantly expressed than in serum. Importantly, we have also provided direct evidence for the existence of a novel B cell lineage uniquely expressing surface IgT. This new lineage represents the predominant B cell subset in the gut-associated lymphoid tissue (GALT) of rainbow trout. More critically, our functional studies have indicated that IgT behaves as a mucosal intestinal immunoglobulin. Thus, we have shown that rainbow trout IgT responses against C. shasta, an intestinal parasite, were only detected in the gut, whereas IgM responses were confined to serum. This finding shows for the first time in a fish, a compartmentalized response of immunoglobulin isotypes into mucosal and systemic areas in response to pathogenic challenge: while IgM plays a predominant role in systemic responses, IgT plays a dominant role in intestinal mucosal surfaces (8) .
One of the hallmarks of mucosal IgA in the gut of humans is its ability to coat a large percentage of luminal bacteria. This IgA coating plays a key role in immune exclusion at mucosal surfaces (28, 29), thus, the IgA-coated bacteria are prevented from attaching and invading the gut epithelium (28, 29). Similar to mammals, the lumen of fish contains high densities of bacteria (30). Supporting the role of IgT in mucosal immunity, we found that a majority of trout intestinal bacteria were found coated with IgT. Our findings collectively point to the first reported non-tetrapod immunoglobulin specialized in mucosal immunity. These findings have recently been published in the 2010, September issue of Nature Immunology (8) and they have made its cover.
3.3 Significance for the area of fish health: From an applied perspective, our findings are expected to have a profound impact in the area of fish health and vaccinology. In that regard, IgM has been considered up until now, the only functional immunoglobulin in teleost fish. Our findings challenge this current view since we show that teleost fish contain not one, but two functional immunoglobulins IgM and IgT that respond to pathogenic challenge. Significantly, all studies carried out in teleost fish during the last few decades have missed to examine the specific contribution of IgT in protecting fish. Thus, our new capability of measuring not only IgM but also IgT responses, will greatly facilitate the evaluation and understanding of fish immune responses as well as the protective effects of fish vaccines. Consequently, this new knowledge is likely to influence the future design of more efficacious fish vaccine formulations that not only stimulate systemic (IgM responses), but also mucosal immunity (IgT responses).
This work was supported by the National Science Foundation (NSF-MCB-0719599 to J.O.S.), and the United States Department of Agriculture (USDA-NRI 2006-01619 and USDA-NRI 2007-01719 to J.O.S.).
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Infectious Salmon Anemia in the Chilean Salmon Farming Industry: Origins and Impacts
Alicia Gallardo Lagno*
Aquaculture Unit, National Fisheries Service. Victoria 2832, Valparaíso, Chile. firstname.lastname@example.org
General Background. Infectious Salmon Anemia (ISA) is a disease caused by an RNA virus belonging to the family Orthomyxoviridae. It mainly affects Atlantic salmon (Salmo salar). The ISA virus was first diagnosed in Norway in 1984; later the infection was confirmed in New Brunswick, Canada (1996), Scotland (1998), USA (2000) and the Faroe Islands (2000). In all these countries, outbreaks of ISA have caused serious economic losses due to high mortalities, and the culling of sick animals at affected sites.
In Chile the first case of ISA was discovered in July 2007 in the primary farmed salmon species, Salmo salar. The disease was present in the central zone of Chiloe (south) from where it spread to the entire X, XI and XII regions. Outbreaks of the disease caused high mortality (~85%) and closure of complete production facilities as a measure of disease control. The development of ISAV was associated in many cases the presentation of parasite outbreaks Caligus rogercresseyi (caligidosis). While not directly causing mortality, infection by the parasite may cause stress in the fish, increasing their susceptibility to other diseases, such as ISA.
The health crisis caused by ISA has led to a decrease of approximately 50% in production of Atlantic salmon in Chile and the loss of about 20,000 jobs in affected regions. Jobs lost include those associated with the production and processing of the farmed fish.
Surveillance and control actions. As control measures, the National Fisheries Service (Sernapesca), established in August 2007, a specific program of surveillance and control of caligidosis. As a result of the program, prevalence was determined to be close to 90% in salmon farms and sea estuaries. Within this program of parasite control, Sernapesca promoted the medicated baths (pyrethroid, deltamethrin), which added to oral treatments using benzoate emamectin. During the first stage of implementation of the program, loads were reduced by 50%. In addition, after the outbreak, Sernapesca established a contingency plan based on existing ISA programs in other countries. In 2008, the following regulations were implemented:
• Additional and complementary measures concerning the importation of eggs.
• Establishment of a technical standard for solid waste management and plant effluent disinfection process fish salmon fishing from areas quarantined for ISA.
• Implementation of a formal system of controlled export by implemented by issuing a health certificate (given previous analysis ISAV negative.)
Our program of surveillance and control of ISA, which established programs for ISAV sampling prior to planting and harvesting, involved active surveillance sampling with emphasis on areas of regional importance (freshwater and seawater). The official method of surveillance used RT-PCR methods.
During 2009 regional zoning was established to facilitate management areas in regions X and XI. Modifications were incorporated into management strategies to reduce mortality. These modifications included mandatory fallow periods, restrictions on movements of saltwater culture facilities, among others. In 2010 the General Law on Fisheries and Aquaculture was amended to add new powers to the health authority, strengthening the franchising model and expanding health control measures. Further, standardized procedures within the Sernapesca network were developed for improved diagnostics, and use of multiple laboratories: Reference Laboratory of the World Organization for Animal Health, and the University of Prince Edward Island in Canada. Results compared between these facilities suggest good inter-laboratory agreement.
Results of the ISA Surveillance Program. The incidence of ISAV from sea farms peaked in 2008, and then decreased in 2009 and 2010. The decline was associated with the elimination of infective cages, and eliminating susceptible individuals. Freshwater (lake) monitoring revealed the presence of viral genome compatible with the ISA virus in breeding farms rearing fry and smolts. Although these specimens did not show the disease, they were eliminated as a precautionary measure, since you do not know their real impact on the epidemiology of the disease, potentially coming from the eggs of positive individuals. To date, there are no outbreaks of disease and the variant of the predominant virus is avirulent (HPR0) in both freshwater (breeding) and sea.
Conclusions. According to the history of the cases reviewed during surveillance, Infectious Salmon Anemia is regarded as prevalent in southern Chile. With an understanding of the stressors that exist for farmed salmon, is expected that new cases of the disease will be observed in different regions, based on the experience of other countries regarding the behavior of this disease.
Based on viral presence in freshwater phase fish we now see a different scenario compared with recognized standard for this disease. This is currently under investigation in order to prevent disease spread, and is a priority in the monitoring and control program. The surveillance system implemented in Chile covers the entire production cycle of salmon. Regulatory amendments and biosecurity measures have been included to consider the risk factors for disease observed in epidemiological studies from Norway, Scotland, USA, Canada, Faroe Islands and Chile. Risk factors include proximity between culture sites and different processing plants, sea fish movement, cage density, fallow periods and parasite loading.
Bravo S, Mydtling P The use of fish vaccines in the Chilean salmon industry (1999-2003) Aquaculture 270 (2007) 36-42
Chile, Servicio Nacional de Pesca, Balance Sanitario de la Acuicultura 2008, www.sernapesca.cl
Gustafson L., Ellis, S; Barrlett CA, Using expert opinion to identify risk factors important to infectious salmon anemia(ISA) outbreaks on salmon farms in Maine, USA and New Brunswick Canadá Prev. Vet. Med. 2005 70: 17-28.
Scotland, Joint government/industry working group on ISA. A code practice to avoid minimize the impact of infectious salmon anemia (ISA) 2000
McClure CA, Hamell K, Dohoo IR. Risk factors for outbreaks on infectious salmon anemia (ISA) in farmed atlantic salmon, salmo salar Prev. Vet. Med. 2005 72 263-280
Godoy M. Aedo A Kibenge JT Groman DB Yason AC Grothusen Hlisperguer a Avendaño F Imilan M Jarpa M Kibenge F First detection, isolation and molecular characterization of infectious salmon anemia associated with clinical disease in atlantic salmon farming (Salmo salar) in Chile BMC Veterinary research 2008 4-28
Short and Long Term Implications for Ecosystem Health in the North Central Gulf of Mexico following the Deepwater Horizon Oil Spill
Dauphin Island Sea Lab, 101 Bienville Boulevard, Dauphin Island, AL 36525 USA email@example.com
A combination of extraordinary productivity,
resulting from the pulsed nutrient inputs from some of the nation’s largest
watersheds, and an abundance of critical nursery habitats have led the north
central Gulf of Mexico to be characterized by many as the nation’s “Fertile
Crescent.” These two ecologically
critical factors have led this region to serve as home for many of the nation’s
economically important fin and shellfish. Moreover the biological diversity of
the north central Gulf of Mexico rivals that of most marine locations in the
northern hemisphere. As such,
proactive management actions that provide for the wise stewardship of the
resources found in this region of the Gulf of Mexico are of paramount
importance to the nation’s environmental health and well being.
A combination of extraordinary productivity,
resulting from the pulsed nutrient inputs from some of the nation’s largest
watersheds, and an abundance of critical nursery habitats have led the north
central Gulf of Mexico to be characterized by many as the nation’s “Fertile
Crescent.” These two ecologically
critical factors have led this region to serve as home for many of the nation’s
economically important fin and shellfish. Moreover the biological diversity of
the north central Gulf of Mexico rivals that of most marine locations in the
northern hemisphere. As such,
proactive management actions that provide for the wise stewardship of the
resources found in this region of the Gulf of Mexico are of paramount
importance to the nation’s environmental health and well being.
The once historically great abundance of these desirable natural resources, coupled with the profusion of coastal tourist opportunities, shipping, and mineral exploitation, have allowed an ever increasing number of U.S. citizens in this region to enjoy the high quality of life found along the Gulf coast, and a bright and sustainable economic future. As a result the productivity the Gulf of Mexico have allowed the region’s commerce to now play a key role in determining the GNP of the US economy.
From the continued exploitation of these ecosystem services provided by the Gulf of Mexico have come a number of human-induced challenges to the ecological health of the Fertile Crescent. The persistent cumulative impacts of these anthropogenic insults have brought many to hypothesize that the Gulf of Mexico has been brought to a tipping point in which much of the what the Gulf of Mexico once provided in abundance could be lost if additional perturbations are added to this already stressed ecosystem.
Situation and Need
On April 22, 2010, the semi-submersible drill platform Deepwater Horizon sank in nearly 1,200 m of water in the northern Gulf of Mexico. After several attempts to close a failed blowout preventer valve, it became clear that estimates of 600 m3 (with unofficial estimates as high as 4,000 m3) of oil were being released each day. Pre-approval of chemical dispersants (CorexitTM) was made based on knowledge of the dispersant application over limited areas and for limited time at the sea surface. However, in this case, an unprecedented volume of dispersant has been applied both at the surface and through direct injection into the wellhead leak at 1,200 m depth. While (primarily) Federal agencies (NOAA, EPA, USCG/DHS) are seeking rapid answers to the toxicities of the dispersants used at these concentrations, with duration and depth constructs considered, emphasis is now focused on discerning how the dispersants impact finfish, shellfish, turtle and bird safety and health. (http://www.noaanews.noaa.gov/stories2010/20100511_sciencechief.html)
Moreover, reactive dispersants are held as trade secrets, though generally these have both solvent and surfactant fractions known to carry toxicity. To date there is no plan for understanding functional ecosystem shifts as a consequence of this magnitude of application of dispersants or the resulting re-distribution of oil or released compounds within the water column.
At this moment, we should be more impressed by what we don’t know than what we do know. Improved documentation and understanding of the physical and chemical impacts of unintended release and dispersal of oil and natural gases, along with the currently employed management strategy of applying chemical dispersants to reduce the areal extent of the oil slicks, is key to achieving a balance between the need to effectively manage our nations dwindling coastal resources and the need to meet the petroleum-based requirements of our nations recovering economy.
The “incident” was initially described with the terms “pre-spill” and “post-spill” but the duration was of such great length that the process of assessing impacts became much more complicated. The chaotic nature of the incident itself was almost overshadowed by the unprecedented interplay between the federal government, local government and BP as the “Responsible Party.” The predictable hysteria generated by the “abundance of enthusiasm” from the media, globally, exacerbated all impacts, particularly in the human dimension of the coastal communities associated with the region bounded by the Mississippi River mouth and Cape San Blas to the East.
Largely into the true post-spill era at time of writing, the emphasis is now focused on calculating damages and cost of restoration. Calculation of habitat impacts is compromised by the fact that the Gulf, in general and not just the north central area, has been ignored and abused for decades, in part because the Mississippi River watershed drains such an enormous area of North America. It is a little known fact that the Mobile Bay watershed is the second largest in the Gulf and forth by volume on the continent.
The confusion associated with what became the worst aquatic oil spill in the nation’s history, and the complexity of the crude oil, contributed to overall impact in various habitats of the Gulf. Originally the concerns were greatest for the extraordinarily productive areas of submerged aquatic grasses, the emergent marshlands, and the oyster reefs of the estuaries. Human emotion and the accompanying economic benefits of the beaches raised their plight despite the fact that they were least endangered and most easily cleaned.
But the use of dispersants on the surface and at depth created the greatest uncertainties. “Out of sight, out of mind” was clearly a motive on the part of BP and optimistically hoping that it could be kept off the shoreline habitats drove most of the decision-making process. The use of dispersants has a technical logic because the smaller the particles, the more rapid the microbial degradation – and hindsight may support the decision to use it on the surface since the surface spill did indeed disappear relatively rapidly. The short term impacts on the existing fisheries has been quite limited with the exception of mortality among the higher vertebrate fauna, particularly seabirds and sea turtles. The impact on zooplankton components of the north central ecosystem may certainly be significant but was unknown at time of writing. There will almost certainly be impacts since it is the eggs and larval stages that exist are the most sensitive and the losses will be reflected in coming harvests.
However, the use of dispersants at depth has created profound uncertainty regarding the fate and effects of a much-debated amount of the crude released. This oil and oil-dispersant mixture never reached the surface where sunlight and abundant oxygen contribute significantly to the natural degradation processes. It is these subsurface “plumes” of hydrocarbons that continue to threaten the ecosystem and perhaps the food chain leading to humans. Certainly the agencies responsible for human health will have to pay attention to the plausible problems of toxic biomagnification.
According to the National Research Council’s assessment “Oil in the Sea III: Inputs, Fates, and Effects, 2003” the only long-term issue is the possible bioaccumulation of polycyclic aromatic hydrocarbons (PAHs). The advantage in this case is that, in contrast to mercury, PAHs are biodegradable by some of the microbial species. So the seminal issue will be the relative success of the competing processes – bioaccumulation or biodegradation. At the moment, the latter appears to be the more likely and the threat may be minimal.
There are some conclusions to be drawn for the moment. The governments, federal or local, do not have the capacity to control such a spill, only the industry has that capacity. But the industry has limited capacity to recover the oil from the environment and has no capacity to deal with the cleanup near the shore. The reliance on industry is a consequence of the Oil Pollution Act of 1990 and there will have to be serious review of that legislation in the aftermath of this 2010 disaster.