The walleye epidermal hyperplasia viruses are two species of

retrovirus A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase ...

es classified under ''

Epsilonretrovirus ''Epsilonretrovirus'' is a waterborn genus of the ''Retroviridae'' family. It infects fish. The species include ''Walleye dermal sarcoma virus'', and ''Walleye epidermal hyperplasia virus 1 The walleye epidermal hyperplasia viruses are two spec ...

'', a genus in the family of ''

Retroviridae A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase e ...

''.Epsilonretrovirus
Viral Zone There are three genome sequenced and identified

exogenous In a variety of contexts, exogeny or exogeneity () is the fact of an action or object originating externally. It contrasts with endogeneity or endogeny, the fact of being influenced within a system. Economics In an economic model, an exogeno ...

retroviruses of this genus which include two known types (WEHV-1 and WEHV-2) associated with walleye epidermal hyperplasia disease. Both viral types are confirmed to be the causative agents of the

neoplastic A neoplasm () is a type of abnormal and excessive growth of tissue. The process that occurs to form or produce a neoplasm is called neoplasia. The growth of a neoplasm is uncoordinated with that of the normal surrounding tissue, and persists ...

condition in the freshwater fish species, the North American

walleye The walleye (''Sander vitreus'', synonym ''Stizostedion vitreum''), also called the yellow pike or yellow pickerel, is a freshwater perciform fish native to most of Canada and to the Northern United States. It is a North American close relat ...

''(Sander vitreus)''. The specific association of retroviral infection with proliferative lesions in fish is based on the presence of retrovirus-like particles (observed via electron microscopy) and

reverse transcriptase A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, ...

activity (using reverse transcriptase

polymerase chain reaction The polymerase chain reaction (PCR) is a method widely used to rapidly make millions to billions of copies (complete or partial) of a specific DNA sample, allowing scientists to take a very small sample of DNA and amplify it (or a part of it) t ...

techniques) from neoplastic tissue. Although both virus types have been observed in lesions of diseased fish, each cell of the infected tissue is host to a specific virus. Transmission studies have also shown that WEHV-2 has been the more proliferative agent of the condition as compared to WEHV-1.

Phylogeny

Phylogenetic analysis of the three confirmed

es shows they are related. After cloning techniques, sequence analysis determined that WEHV-1 and WEHV-2 are similar in size and share 95%

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

identity in the ''pol'' region of

. This finding suggests that they are different strains of the same virus or likely distinct species. The two types of WEHV also share over 80% of their amino acid sequence with the third member of the epsilonretrovirus genus. Included in this analysis was the observation of a homologous genomic organization in all three Epsilonretroviruses.

Condition

Walleye epidermal hyperplasia lesions are characteristically broad, flat, translucent plaques that range in size (2–50 mm in diameter). Lesions are most often observed in sexually mature fish although transmission studies have shown that fingerling fish can be infected using cell-free virus components extracted from lesions. Multiple growths are also known to coalesce into larger lesions. Seasonal observations of the fish by scientists and sportsmen show a high incidence of the condition during the late fall, winter, and early spring months. Mortality in the host fish is hypothesized to be less related to the virus and more to secondary infections that invade necrotic tissue. These viruses have evolved a means to maintain a fine balance between its own proliferation and leaving behind a fit and reproductive host.

Transmission and epidemiology

As with other skin lesion retroviruses, the in-lake transmission of the WEHV particles appears to be the result of contact with water harboring released infectious viral particles or close contact with other fish. The infection proliferates in temperatures between 0–5 °C (32–41 °F), and this may be why it occurs primarily in the fall and spring. With this seasonal prevalence, it is suggested that an inverse relationship exists between water temperature and skin lesion size/abundance. This is especially evident in the fact that few walleye show signs of the condition during the summer months. The nature of the seasonality of this condition is linked to a couple possible hypotheses: (1) low water temperatures and immune suppression, and (2) the physiological stress associated with spring spawning It is important to note that this disease is not classified as

zoonotic A zoonosis (; plural zoonoses) or zoonotic disease is an infectious disease of humans caused by a pathogen (an infectious agent, such as a bacterium, virus, parasite or prion) that has jumped from a non-human (usually a vertebrate) to a human. ...

and is not known to infect humans.

Molecular biology and oncogenesis studies

Molecular studies of retroviruses have been partly responsible for elucidating the mechanisms responsible for

oncogenesis Carcinogenesis, also called oncogenesis or tumorigenesis, is the formation of a cancer, whereby normal cells are transformed into cancer cells. The process is characterized by changes at the cellular, genetic, and epigenetic levels and abnor ...

. The Epsilonretroviruses provide a unique model for understanding the development and regression of tumors due to its seasonal prevalence and genetic evolutionary baggage. Proteins encoded by these viruses function in cell cycle regulation, alteration of cell-signaling pathways to promote proliferation and suppression of host cell apoptosis, and induction of apoptosis. The genetic and transcriptional similarities of the three classified ''Epsilonrertovirus'' suggest that these viruses share homologous mechanisms to replicate and proliferate.

References

{{Taxonbar, from=Q18976265, from2=Q18976268 Epsilonretroviruses Fish viral diseases Unaccepted virus taxa