Fish Can Get Diseases Too

Infectious diseases are increasingly recognized as an important component of the ecology of fish in the wild. Many of the viral, bacterial, protozoan and fungal pathogens of fish that were initially discovered in captive fish have their origin among wild populations; however, the impact of disease among these free-ranging stocks has been difficult to study. At the WFRC, combinations of field and laboratory investigations, aided by the tools of molecular biology, have begun to provide information on the ecology of infectious diseases among natural populations of fish in both freshwater and marine ecosystems. A researcher at the WFRC removes the anterior kidney from a rainbow at a sterile workstation. Cells from the anterior kidney are used to study various aspects of fish health including /pathogen relationships, vaccine efficacy and the effects of hatchery rearing The following diseases or pathogens of free-ranging practices. populations of finfish have been studied at the WFRC:

Bacterial kidney disease that affects the ability of Ceratomyxa and trying to predict the influence of juvenile Pacific to Parvacapsula infections disease in the survival of juvenile migrate downstream and to of juvenile salmon in the salmonids exposed to various survive in the ocean. Klamath River. stressors during their outmigration.

Infectious hematopoietic Ichthyophoniasis in How are Bacterial Diseases necrosis virus that can adult in Diagnosed in Fish? cause high losses among the Yukon River. salmon fry. Bacterial and viral diseases can In addition, new studies, using have a great negative impact on Whirling disease that state-of-the-art molecular salmonid populations, especially in affects wild-spawning biology techniques such as the a hatchery setting. Some of these in the Rocky polymerase chain reaction and diseases kill many fish very Mountain West. cDNA microarrays, are aimed at quickly, others are slower to take hold but are also very deadly to Viral hemorrhagic fish. For these reasons, it is septicemia in marine fishes important to quickly identify any of northern Puget Sound. potential infection so that appropriate action can be taken to Ichthyophthirius and isolate, and often treat, the disease in pathogen before an epizootic (an returning adult salmon in epidemic in ) can occur. the Klamath River. Juvenile Chinook salmon with bacterial kidney disease.

U.S. Department of the Interior USGS FS 2006-3066 U.S. Geological Survey July 6, 2005 We use several diagnostic techniques to identify the presence of specific Microscopic Slides of Bacteria bacteria in salmonids. Some of these methods were developed in our laboratory and are now used for diagnosis of bacterial fish diseases in many Gram- parts of the world. (See sidebar) Positive

Bacteria Salmonid Immune Function

Gram- Anadromous salmonids are Negative susceptible to a variety of disease Bacteria causing (pathogenic) micro- organisms, including at least 30 bacteria and viruses. Whereas the impact of these microorganisms on Fluorescing Young salmon fry may have been infected Bacterial salmonids in wild and natural with the kidney disease bacterium before rearing areas is difficult to measure, they hatched from the egg. losses from disease among hatchery salmonids are both common and requires the minimization of well documented. The disease state environmental stressors such as Gels depends on 3 factors, the host (fish), handling, high rearing densities the disease organism, and the and poor water quality, while environment. maintaining the carrying capacity of the facility. Unfortunately, there

Bacterial Disease is not the result of a single is no simple measure of the health Proteins event, rather the consequence of an status of a fish population. Since imbalance in the host-pathogen the immune system of any higher relationship. The presence of a organism is essential for its well pathogen in a salmon population being, measures of the fishes will not always result in losses due defenses provide an attractive to disease and fish can remain means to quantify fish health. asymptomatic carriers under However, we are only beginning to favorable conditions. However, understand the immune system of Amplified stressors exceeding the limits of a Bacterial salmon, and how it modulates with DNA fish's physiological tolerance will seasonal and life stage changes, or diminish its ability to resist disease, differing rearing conditions. and consequently, become a threat to its health. Renibacterium salmoninarum

For salmon, the hatchery environ- Bacterial Culture Plates Renibacterium salmoninarum is ment is quite different than the the causative agent of bacterial environments they inhabit in the kidney disease (BKD), a serious wild. Successful fish husbandry disease problem of wild and

Bacterial Colonies

ELISA Assay The kidney disease bacterium can be detected in fish tissues by the fluourescent Bacterial test. Antigen Detected cultured salmonid fishes worldwide. Control of the bacteria by use of antibiotics is difficult due to its slow growth, and conventional vaccine strategies are ineffective or may actually worsen the disease state. Furthermore, the bacteria can be passed not only between fish in the same water system (horizontal transmission), but also from one generation to the next via infected eggs (vertical transmission). During infection, R. salmoninarum can evade immune surveillance by surviving and replicating within host macrophages (a type of white blood cell). Also, R. salmoninarum produces large amounts of a unique protein (p57) which suppresses a number of immune functions. Control of R. salmoninarum will require a better understanding of the bacteria itself, the salmonid immune system and how the bacteria and host defenses interact. A toolbox of immunological assays is used to monitor the defenses of fish infected with the kidney disease bacterium. Whirling Disease

Myxobolus cerebralis is a several trout streams in IHN Virus metazoan parasite that penetrates and were attributed to the head and spinal of whirling disease. Subsequently, a Infectious haematopoietic necrosis fingerling trout where it multiplies large, ongoing survey revealed that (IHN) is an infectious viral disease very rapidly, putting pressure on naturally spawning rainbow and of salmon and trout. It was first the organ of equilibrium. This in many western rivers recognized in the 1950s in sockeye causes the fish to swim erratically were infected with the parasite and chinook salmon. The disease (whirl), and have difficulty feeding with some of the fish showing has the most economic significance and avoiding predators. In severe clinical disease. Of additional for freshwater farms, however infections, the disease can cause concern was the presence of Pacific and ( high rates of mortality in young-of- whirling disease in native stocks of salar L.) in both fresh and sea the-year fish. Those that survive cutthroat ( clarki) water have been severely affected. until the cartilage hardens to and ( can live a normal life span, but are confluentus) which are of special marred by skeletal deformities. status due to their declining Lightly infected fish can, however numbers. Improved reproduce without passing on the diagnostic methods parasite to their offspring. now provide epizoo- tiological information Whirling disease has become a about strains of the highly significant problem for parasite or the alternate managers in federal and host. state agencies throughout the nation. Thought to have been introduced from Europe, whirling disease was first detected in the U. S. in 1958 and has now been Bull trout (Salvelinus confluentus) reported from fish in more than 20 states. The potential for whirling disease to cause losses in natural stocks of trout became a national concern in 1993-1994 when losses of up to 90% of the wild rainbow trout (Oncorhynchus mykiss) in Deformed skeletons of 8-moonth old rainbow trout (Oncorhynchus mykiss) with whirling disease. Fry and small fingerlings become characterize the specific virus type, Additional Reading infected very readily, becoming more and compare it with other known

resistant as they mature. The IHNV types in our database. Miller, K.M., J.R. Winton, A.D.

infection is often lethal and the Similar methods are used for other Schulze, M.K. Purcell, and T.J. mortality rate can be 100% in fry. fish viruses and for epidemics of Ming. 2004. Major histocompati- Some fish that survive an outbreak of flu, SARS, and anthrax. Over 600 bility complex loci are associated IHN may become carriers of the IHN virus samples from with susceptibility of Atlantic virus, providing a reservoir of throughout the Pacific Northwest salmon to infectious hematopoietic infection. In addition, infected have been characterized to date. necrosis virus. Environ. Biol. juveniles shed IHN virus particles in Fishes 69: 307-316. the faeces, urine and external mucus. tudies have revealed that S Kocan, R.M., P.K. Hershberger, infectious diseases can cause major Researchers at the WFRC are and J. Winton. 2004. creating a set of molecular tools by losses in populations of free- Ichthyophoniasis: An Emerging cloning each of the viral and ranging fish and are significant Disease of Chinook Salmon

sequencing the entire genome. This factors in the ability of certain (Oncorhynchus tshawytscha) in the information is stored in an IHN stocks to recover. Work has also Yukon River. J. Aquat. Anim. database. When an IHN virus served to highlight the critical role Health 16:58-72. epidemic occurs, our researchers use played by environmental molecular genetic methods to conditions and other sources of Anderson, E.D., H.M. Engelking, stress in the ecology of fish E.J. Emmenegger, and G. Kurath. diseases. 2000. Molecular epidemiology reveals emergence of a virulent infectious hematopoietic necrosis Development of a novel vaccine for IHN (IHN) virus strain in wild salmon

and its transmission to hatchery IHN virus is a severe pathogen of salmon and trout that causes epidemics with 20- fish. J. Aquat. Anim. Health

90% mortality. It is in the same virus family as the rabies virus. There is currently no 12:85-99. commercially available vaccine for IHNV. Signs of IHN Allen, B.M., E.P. Bergersen. 2002. Factors influencing the distribution of cerebralis, the causative agent of whirling disease, in the Cache la Poudre River, Colorado. Dis. Aquat. Org. 49:51- 60.

A complete list of WFRC Here at WFRC we work with development of a novel DNA vaccine to protect fish publications can be found on against IHN virus. Left: The vaccine, pIHNV-wG, is a circular piece of DNA our website at: that carries the for the IHNV surface protein G. Right: The IHNV DNA vaccine will be tested against a placebo (control) vaccine to confirm protection http://wfrc.usgs.gov/pubs/pubs.htm against the disease.

IHNV G Luciferase For additional information, please contact:

Lyman Thorsteinson, Center Director pIHNV-wG pLuc U.S. Geological Survey Western Fisheries Research Center 6505 NE 65th Street Seattle, WA 98115

IHNV Control mock Phone: (206-526-6282 FAX (206) 526-6654 DNA Vaccine DNA Vaccine http://wfrc.usgs.gov