Viral Hemorrhagic Septicemia Virus Figure 1 microscopic look at viral hemorrhagic septicemia courtesy of http://cpw.state.co.us/learn/Pages/AAHLEmergingDiseasesIssues.aspx Jared Remington Aquatic Invasion Ecology University of Washington Fish 423 A Autumn 2014 December 5, 2014 Classification conducted by examining infected fish. Living specimens will appear either lethargic or over Order: Mononegavirales active, making sporadic movements, such as circles or corkscrews. Deceased specimens can Family: Rhabdoviridae appear dark in color, have pale gills, bloated Genus: Novirhabdovirus abdomen, fluid filled body cavity, bulging eyes, and most notably external and internal Species: Undescribed hemorrhaging or bleeding. External hemorrhaging will typically take place around Known by the common name Viral the base of fins, eyes, gills, and the skin. Internal Hemorrhagic Septicemia Virus, or in Europe hemorrhaging can be found in the intestines, air Egtved disease, you may find it abbreviated as bladder, kidneys, liver, heart, and flesh VHSV, VHSv, or VHS. Viral Hemorrhagic (McAllister, 1990; Marty et al., 1998; Kipp& Septicemia is part of the family Rhabdoviridae Ricciardi, 2006; Bartholomew, et al. 2011). which also includes the famous rabies virus which can affect humans and other mammals. Not to worry VHS does cannot infect humans, handling or consuming and infected fish will not result in contraction of the virus. The virus is exclusive to fishes. VHS is related to another famous fish killer, the infectious hematopoietic necrosis virus, both are part of the genus Novirhabdovirus. Identification Much like other rhabdoviruses, viral hemorrhagic septicemia (VHS) contains RNA within a bullet/cylindrical shaped shell made of Photo contains gizzard shad infected with viral glycoprotein G, the virus ranges from about 170- hemorrhagic septicemia, visual external 180nm long and 60-70nm wide (Elsayad et al. 2006; McAllister 1990; Kipp & Ricciardi 2006). hemorrhaging. Photo credit to Dr. P. Bowser, Aquatic Animal Health Program, CVM, Cornell University. http://www.cfsph.iastate.edu/DiseaseInfo/disease- images.php?name=viral-hemorrhagic- septicemia&lang=en Figure 2 photo illustration of a Novirhabdovirus showing the RNA chain and glycoprotein shell. Courtesy of the Swiss Institute of Bioinformatics http://viralzone.expasy.org/all_by_species/76.html Visual identification can be challenging given the size of VHS, most identification is Photo: rainbow trout with internal signs of viral no mass mortality events, and how it can persist hemorrhagic septicemia, discoloration in the liver, in a population and so many individuals can become carriers of the disease. hemorrhaging in the flesh and intestines, and pale Life cycle gills. Photo by T. Håstein http://www.dfo- When VHS comes in contact with a potential mpo.gc.ca/science/enviro/aquaculture/rd2013/rdhealt host cell the glycoprotein G matches/binds with h-eng.html an entry molecule on the host cellular membrane receptor. The host cell then brings the virus into “Life” history the cell in a process called endocytosis. Then the Viral hemorrhagic septicemia is passed virus membrane and vesicle membrane (of the on to other fish through water. Fish that come in host cell) fuse together. This is when the RNA contact with infected bodily fluids like excretory strands are released into the cytoplasm. The host waste such as urine or feces, or reproductive cell then creates mRNA which is then replicated fluids such as sperm and ovarian fluid, are likely into RNA. This RNA then binds with other to become infected. The virus may also be proteins forming a bud which eventually passed on through physical contact with an separates thus forming a new virus in search of a infected fish touching non infected fish. new host (SIB, 2011). Predatory fish can also become infected through Environmental optima and tolerance consumption of infected fish or a carrier of the disease. The virus can enter a fish through the The optimum temperatures for gills, digestive tract, or an open wound (CFSPH replication is 14-15 degrees Celsius, and the 2007) optimum pH for replication is 7.4-7.8 (Kipp et al. 2014). It was found that VHS does not It is possible for other species to become carriers replicate effectively at temperatures greater than of the disease. Such as predatory birds, which 18 degrees Celsius (Hendrick et al. 2003). ingest infected fish and can transport the virus to Reproduction is also low at temperatures below different locations (CFSPH 2007). Even fresh 6 degrees Celsius. Reproduction stops and VHS water turtles such as the red-eared slider, becomes inactive at temperatures above 20 common snapping turtles, and the yellow-bellied degrees Celsius (De Kinkelin et al., Bernard et slider 10-20 days after consuming infected fish al., McAllister, cited by Kipp et al. 2014). Fish may carry the virus and excrete it into the water; mortality as a result of VHS is highest in where it has the potential of finding a new host temperatures ranging from 3-12 degrees Celsius (Goodwin & Merry, 2011). (McAllister, cited by Kipp et al. 2014). It was The most prolific and problematic carrier of the discovered that VHS can persist in fresh water disease are other fish that do not show signs of from anywhere between 28 to 35 days, and up to the disease, do not die, and in turn become a year if it is in filtered fresh water. VHS can lifelong carriers of the disease passing on the remain infective even longer if present in virus to their fellow cohorts. ovarian fluid (MDTAA, 2009). The incubation period for VHS at warm water Finding the optimum temperature in which VHS temperatures is 1-2 weeks, and 3-4 with cold can replicate can help us establish which bodies water temperatures. Also mortality has been of water are prone to the establishment of VHS. observed in Pacific Herring 4-6 days after being This would help in prioritizing prevention introduced to the virus (CFSPH, 2007). It was methods to stop the spread of the virus into determined by Gary Marty and his associates in favorable habitat. Upper and lower extremes of 1998 that 10-15% of Pacific herring showed no the VHS replication can also help us rule out signs of VHS yet tested positive, they then potential areas where VHS cannot establish, discovered that the herring only expressed the enabling us to send resources elsewhere. The VHS symptoms when under stress. This is why necessity for cold water is one reason why it is populations can have the disease yet experience found in the Northern hemisphere and not in the Southern tropical ocean systems. Biotic associations There are over 82 different fish species affected by viral hemorrhagic septicemia. 23 species in the Great Lake region of the United States have witnessed large scale die offs due to viral hemorrhagic septicemia (MDTAA, 2009). On the Pacific Coast of the United States and Canada die offs of Sardines and herring have been recorded (Marty et al. 1998). Fish species affected by this virus can be found in marine or fresh water across the entire globe. Many of these species are extremely valuable either commercially, recreationally, or ecologically. is an old lineage of VHS present in some mainland lakes of Germany and Denmark. Genotype 1d is present in rainbow trout reared in fresh or brackish water along Norway and Finland. Genotype 1e is found in parts of the Black Sea (He, 2014). In general VHS 1 is highly virulent in rainbow trout and can have a high mortality rate which can reach up to 100% in trout fry (CFSPH, cited by Kipp et al. 2014). The geographic range for VHS genotype 2 is the Baltic Sea, found mostly in herring, cod, and sprat. This genotype has not been associated with any disease outbreaks and or die-offs (Emmenegger et al. 2013). VHS genotype 3 is found in the marine waters of Figure 5 lists all of the currently known fish species the North Sea and North Atlantic off the coasts that have at one time tested positive for VHS. VHS of Norway and Great Britain. This strain of VHS only infects marine species such as turbot and affect 13 orders of both marine and fresh water rainbow trout raised in marine net pens species. This table is from the Manual of Diagnostic (Emmenegger et al. 2013). Tests for Aquatic Animals. There are several sub classes of type 4 VHS http://web.oie.int/eng/normes/fmanual/2.3.09.VHS.p typically referred to as the North American strain. First, type 4a is found in the Pacific df Ocean from Alaska to California and in parts of Japan and Korea. Type 4b is found in the Great Geographic distribution Lakes and several other mid-west lakes and rivers. Type 4c is found in the North Atlantic There are four types of viral along the Eastern Canadian coast (He et al., hemorrhagic septicemia, based off of geographic 2014). Genotype 4 the North American strain location, types 1 and 4 are further broken down can be highly virulent in herring, sardines, and into subdivision genotype 1 is broken down into other fresh water species with a mortality rate subtype a-e, and type 4 is broken down into a-c. anywhere from 20-80%. However it is less VHS genotype 1a is covers the terrestrial water virulent in salmonids, compared to the European bodies of Europe, this subtype represents the type 1 (Follett et al., 1997; CFSPH, 2003; initial discovery of VHS in the European Emmenegger et al. 2013; Kipp et al. 2014). aquaculture industry. Type 1a likely diverged from a marine source 60 years prior to its discovery (Kim et al. 2014). Genotype 1b is associated with the marine area of the Southwest Baltic Sea and into the North Sea.