The growing importance of aquatic animal diseases

In recent years, animal disease has emerged as one of the most important factors hindering the development of aquaculture worldwide. This is one of the largest global sectors of agriculture, exceeding or rivaling all other animal agriculture except for pork, and some health officials worry that animal disease problems will increase as the aquaculture industry grows. According to many who attended a special biosecurity symposium during Aquaculture 2004 this past March, aquaculture biosecurity must be improved around the world.

"The symposium's strong consensus (was) that the issue of aquaculture biosecurity is continuing to be important and some concerted action is imperative to reduce the impacts worldwide," says Rohana Subasinghe, PhD, senior resources fishery officer in the Fisheries Department of the United Nations Food and Agriculture Organization.

Aquaculture 2004—a meeting of the National Shellfisheries Association, the fish culture section of the American Fisheries Society, and the World Aquaculture Society— was held in Honolulu and attracted veterinarians and scientists from around the world. The biosecurity symposium, sponsored in part by the AVMA, spanned two and a half days and was the first international meeting of its type to have a primarily veterinary, as opposed to biology, thrust.

Are we burning our boats?
According to figures from the FAO, aquatic animal production accounts for approximately 47 percent of animal protein production in the world. Most countries with aquaculture industries have had their share of biosecurity problems, and disease outbreaks can be costly.

Two devastating outbreaks of infectious hematopoietic necrosis have occurred in the salmon farming industry in British Columbia in the past 12 years. In each case, the initial introduction of the virus was from the wild, but most of the secondary spread between sites was likely caused by human activity, according to Dr. Grace Karreman, project coordinator for the British Columbia Fish Health Database.

In the United States, two of the four most recent national animal emergency declarations were issued for aquatic animals. The Department of Agriculture declared an emergency for infectious salmon anemia, in 2001, and spring viremia, which affects varieties of carp and related species, in spring 2003.

In many cases, it's only a matter of time before an outbreak in one country becomes a problem for another. White spot disease, which can devastate shrimp populations, was first reported in Taiwan and China in the early 1990s. It was found in many Asian countries shortly thereafter and was identified in the United States in 1995. Since 1999, WSD has been reported in several Central and South American countries. This past April, the Hawaii Department of Agriculture made the first identification of the disease in the Pacific Ocean region of the United States.

Taura syndrome virus, which also infects shrimp, first started in the Americas in 1991 and then spread to Asia. It devastated the U.S. shrimp farming industry and drove many producers to develop shrimp farms in the biosecure, arid regions of Arizona.

In 1995, the OIE released its first edition of the Aquatic Animal Health Code. This code outlines measures that member countries can take to ensure the sanitary safety of international trade in aquatic animals, without setting up unjustifiable barriers. The OIE Manual of Diagnostic Tests for Aquatic Animals provides a uniform approach for diagnosing diseases listed in the Aquatic Animal Health Code, so that requirements for health certification in connection with trade can be met.

Since the 1990s, aquaculture farms, regions, and countries have begun to adopt a variety of biosecurity measures and programs to defend against the spread of diseases. Farms can, for example, exclude specific pathogens from cultured aquatic stocks in broodstock facilities, hatcheries, and farms, or whole countries. Controlling water sources by improving farm design and water management is another method to control disease. Current aquatic biosecurity programs worldwide, however, need improvement.

"The best (aquaculture biosecurity) response plan in place is Australia's AQUAPLAN and AQUAVETPLAN," says Dr. A. David Scarfe, assistant director in the AVMA Scientific Activities Division, who helped organize the biosecurity symposium at Aquaculture 2004. "In all other countries, elements are at various stages of emergence or development."

Canada, Estonia, Norway, New Zealand, Switzerland, the United Kingdom, and the United States are moving vigorously in their development of aquatic animal biosecurity plans. Some other countries have plans in progress, but they don't have a comprehensive commitment or approach, or a clearly formulated plan, according to Dr. Scarfe.

The increased attention to nationally and internationally important endemic and foreign diseases in aquatic animals will place increasing demands on veterinarians.

Fishing for solutions
According to Dr. Karreman, even though the OIE has set importing/exporting requirements for international aquatic animal health, an agreed-to definition of biosecurity at the farm or national level doesn't exist. Hurdles face individuals trying to implement successful aquaculture biosecurity programs. The industry is extremely large and diverse. It has a loose infrastructure, and many aquaculture farmers are unaware of critical issues.

Dr. Scarfe says it has taken decades to formulate and execute biosecurity programs for terrestrial systems, which are now being more functionally refined. By comparison, aquaculture biosecurity is in its infancy. That doesn't mean, however, that programs are starting from scratch. Symposium attendees emphasized that the aquaculture industry must learn, adapt, and refine biosecurity approaches from the experiences of their terrestrial counterparts.

"Aquatic animal biosecurity must involve the competent application of biosecurity concepts and experience from terrestrial species to the aquatic situation," says Dr. Karreman, who is also a veterinarian at Pacific Marine Veterinary Services in Nanaimo, British Columbia. "This includes a quality management system and the efficient use of veterinarians, from the farm to the national level."

Aquaculture can follow animal agriculture's lead, for example, in developing third-party assurance and enforcement. Veterinarians may encounter hurdles that seem familiar.

"In my personal opinion, the biggest obstacle at the farm level is complacency," says Dr. Eva-Maria Bernoth, president of the OIE Aquatic Animal Health Standards Commission. "(Biosecurity is) a bit like insurance, and with such an obscure and possibly never eventuating return on investment, resources are often directed toward more tangible outcomes. The best way to address this is by raising awareness."

Paul Hardy-Smith, a veterinarian at Panaquatic Health Solutions in Hawthorne, Victoria, Australia, says that raising awareness requires hard work and persistence. Farmers who employ keen, motivated people who are proud of their farming will have better luck. Farm employees need to be taught biosecurity skills in applied training settings, not just from books, and farmers need to keep up to date with industry knowledge and maintain good communication channels with their workers.

Farmer awareness isn't the only problem however—symposium attendees pointed out that scientific and technical information on aquaculture biosecurity is scarce.

"We do not fully understand the dynamics of disease transmission in the aquatic medium. This will only come through quality aquatic health management research and through practical, on-site aquatic animal health experience," Dr. Karreman says. "Many unknowns in life cycles of infectious agents may have significant impacts on effectiveness of biosecurity—for example, unknown intermediate hosts for parasites and natural reservoirs for emerging diseases."

Several recommendations came out of a roundtable discussion at the end of the symposium. Veterinarians and scientists should develop clear policies addressing aquatics, and build and improve health and disease plans. They need to gather more scientific information, build information databases, develop management approaches based on sound science and risk analysis, and test biosecurity programs, applying lessons learned to future programs. Farms should expand support personnel and other resources. And finally, collaboration and communication among stakeholders must increase. It is this latter recommendation that the biosecurity symposium has helped.

"The symposium was an excellent means to bring together people that are involved with aquaculture biosecurity at all levels—from the individual farm level to the company level, to the regional or provincial level, to the national and, finally, international level," Dr. Bernoth says. "It quickly became apparent that biosecurity means different things at different levels, and that a concerted and cohesive approach is necessary to understand and implement biosecurity programs as a 'whole-of-chain' concept."

At press time, the FAO and OIE were considering convening an aquatic animal health and biosecurity conference in May 2005.