Salmonid herpesvirus 2 (SalHV-2) is a species of virus in the genus '' Salmovirus'', family ''

Alloherpesviridae ''Alloherpesviridae'' is a family of viruses in the order ''Herpesvirales ''Herpesvirales'' is an order of dsDNA viruses (Baltimore group I) with animal hosts, characterised by a common morphology consisting of an icosahedral capsid enclosed ...

'', and order ''

Herpesvirales ''Herpesvirales'' is an order of dsDNA viruses (Baltimore group I) with animal hosts, characterised by a common morphology consisting of an icosahedral capsid enclosed in a glycoprotein-containing lipid envelope. Common infections in humans cause ...

''. The virus has been referred to as ''Oncorhynchus masou'' virus (OMV) after the disease caused by the virus was first referred to as ''Oncorhynchus masou'' virus disease (OMVD) in 1981.

Background

The virus was first isolated in the ovarian fluid of masu salmon (''Oncorhynchus masou'') in 1971 from a hatchery in

Hokkaido is the list of islands of Japan by area, second-largest island of Japan and comprises the largest and northernmost prefectures of Japan, prefecture, making up its own list of regions of Japan, region. The Tsugaru Strait separates Hokkaidō fr ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

. In later studies, the virus has been found to be

pathogenic In biology, a pathogen (, "suffering", "passion" and , "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ. The term ...

and oncogenic to fish other than masu salmon, including

coho salmon The coho salmon (''Oncorhynchus kisutch;'' Karuk: achvuun) is a species of anadromous fish in the salmon family (biology), family and one of the five Pacific salmon species. Coho salmon are also known as silver salmon (or "silvers") and is often ...

(''O. kisutch''), kokanee salmon (''O. nerka''),

chum salmon The chum salmon (''Oncorhynchus keta''), also known as dog salmon or keta salmon, is a species of anadromous salmonid fish from the genus ''Oncorhynchus'' (Pacific salmon) native to the coastal rivers of the North Pacific and the Beringian Arctic ...

(''O. keta''), and

rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributary, tributaries of the Pacific Ocean in North America and Asia. The steelhead (sometimes called steelhead trout) is an Fish migration#Classification, ...

(''O. mykiss''), though the virus is still referred to by the species it was initially found to have infected. Salmonid herpesvirus 2 primarily affects such

salmonid Salmonidae (, ) is a family of ray-finned fish, the only extant member of the suborder Salmonoidei, consisting of 11 extant genera and over 200 species collectively known as "salmonids" or "salmonoids". The family includes salmon (both Atlantic a ...

fish, both wild and farmed, in Japan, though it has been observed in

Kuwait Kuwait, officially the State of Kuwait, is a country in West Asia and the geopolitical region known as the Middle East. It is situated in the northern edge of the Arabian Peninsula at the head of the Persian Gulf, bordering Iraq to Iraq–Kuwait ...

. Significant economic loss was suffered by the rainbow trout industry in Japan due to the virus, as the resulting disease affected many marketable-sized fish in 1992.

Pathology

Susceptibility to the virus varies between species; species from most to least susceptible are as follows: kokanee salmon, chum salmon, masu salmon, coho salmon, and rainbow trout.

Mortality rates Mortality rate, or death rate, is a measure of the number of deaths (in general, or due to a specific cause) in a particular population, scaled to the size of that population, per unit of time. Mortality rate is typically expressed in units of d ...

also vary based on the age of the fish. In a 1983 study, researchers found that the rate of mortality of young salmon between 1-month and 5-months-of-age was above 80%, with mortality rates decreasing to less than 10% after 6-months-of-age. Clinical signs include the appearance of ulcerated skin lesions, pale gills, darkening of the body surface, anorexia, lethargy, and

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 ...

tissue on the exterior of the fish. Tumours may persist for up to a year after infection in surviving fish. However, some fish were found to show no external signs of ''Oncorhynchus masou'' virus disease despite infection. Internally, white and gray spots on the liver and intestines, and swelling of the liver and intestines have been observed. Transmission of the virus is horizontal, and may be shed through skin, feces, urine, and sexual fluids. Both symptomatic and asymptomatic carriers are able to transmit the virus to others. Replication of the virus and its appearance has been found in the ovarian fluid of mature fish. While surviving fish are not considered a threat to human health, they are considered unfit to be sold due to the presence of skin ulcers and cutaneous tumours.

Treatment

Salmonid herpesvirus 2 has been found to be sensitive to various treatments, such as

ultraviolet Ultraviolet radiation, also known as simply UV, is electromagnetic radiation of wavelengths of 10–400 nanometers, shorter than that of visible light, but longer than X-rays. UV radiation is present in sunlight and constitutes about 10% of ...

irradiation Irradiation is the process by which an object is exposed to radiation. An irradiator is a device used to expose an object to radiation, most often gamma radiation, for a variety of purposes. Irradiators may be used for sterilizing medical and p ...

and

ozone Ozone () (or trioxygen) is an Inorganic compound, inorganic molecule with the chemical formula . It is a pale blue gas with a distinctively pungent smell. It is an allotrope of oxygen that is much less stable than the diatomic allotrope , break ...

and iodophor treatment. Preventative measures include testing ovarian fluid of mature fish within hatcheries, disinfection of fertilized eggs, and disinfection and iodophor treatment of affected facilities.

References

{{Taxonbar, from=Q18965136 Alloherpesviridae