Whispovirus

White spot syndrome virus (WSSV) is the lone virus (and type species) of the genus Whispovirus (white spot), which is the only genus in the family Nimaviridae. It is responsible for causing white spot syndrome in a wide range of crustacean hosts. White spot syndrome (WSS) is a viral infection of penaeid shrimp. The disease is highly lethal and contagious, killing shrimp quickly. Outbreaks of this disease have wiped out the entire populations of many shrimp farms within a few days, in places throughout the world.White spot syndrome virusThe first reported epidemic due to this virus is from Taiwan in 1992; however, reports of losses due to white spot disease came from China in 1993, where it led to a virtual collapse of the shrimp farming industry. This was followed by outbreaks in Japan and Korea in the same year, Thailand, India and Malaysia in 1994, and by 1996 it had severely affected East Asia and South Asia. In late 1995, it was reported in the United States, 1998 in Central and South America, 1999 in Mexico' in 2000 in the Philippines, and in 2011 in Saudi Arabia. The virus was detected in Queensland, Australia in November 2016. Australia was believed to be the last shrimp-growing region free from the virus.White spot syndrome virus is a species of virus in the genus Whispovirus, in the family Nimaviridae. It is the only species in this family, so serves as the type species.The virus has a wide host range. While shrimp can survive with the virus for extended periods of time, factors such as stress can cause the outbreak of WSS. The disease is highly virulent and leads to mortality rates of 100% within days in the case of cultured penaeid shrimps. Most of the cultured penaeid shrimps (Penaeus monodon, Marsupenaeus japonicus, Litopenaeus vannamei, and Fenneropenaeus indicus) are natural hosts of the virus. Several nonpenaeid shrimp were also found to be severely infected during experimental challenges. Many crustaceans such as crabs (Scylla spp., Portunus spp.), spiny lobsters (Panulirus spp.), crayfish (Astacus spp.', Cherax spp.) and freshwater shrimp (Macrobrachium spp.) are reported to be infected with variable severities depending on the lifestage of the host and presence of external stressors (temperature, salinity, bacterial diseases, pollutants).In the host, WSSV infects a wide variety of cells from ectodermal and mesodermal origin. Histological changes are seen in the gill epithelium, antennal gland, haematopoeitic tissue, nervous tissue, connective tissue, and intestinal epithelial tissue. Infected cells have prominent intranuclear occlusions that initially stain eosinophilic, but become basophilic with age; hypertrophied nuclei with chromatin margination; and cytoplasmic clearing. Pathogenesis involves widespread tissue necrosis and disintegration.Infection with WSSV differs from other described penaeid infections yellowhead virus (YHV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV) in the described histological findings, as YHV has a reduced tissue specificity, infecting only the intestinal epithelial tissues and IHHNV causes intranuclear occlusions that stain eosinophilic, but do not change over the course of the infection.No treatments for WSS are available.A large number of disinfectants are widely used in shrimp farms and hatcheries to prevent an outbreak. Stocking of uninfected shrimp seeds and rearing them away from environmental stressors with extreme care to prevent contamination are useful management measures. Site selection may be one of the most crucial in preventing WSS. Shrimp farmed in areas with relatively low temperature fluctuations and at water temperatures greater than 29°C had increased resistance to WSSV.