White Spot Disease (WSD) is a viral infection caused by Whispovirus that causes death in up to 80% of affected farmed prawns. The disease begins with lack of appetite, uncoordinated movements and lethargy in affected animals, leading to death within a few days. White spots may or may not be present towards the final stages of the disease. The disease also infects crabs, lobsters and some marine worms, but these carry and spread the disease without showing any symptoms. The virus is not related to the fish disease also known as White Spot. WSD is harmless to humans and infected prawns can be eaten with no harmful effect.
The disease is rarely fatal in wild animals, but is fatal in farmed animals. Farmed prawns are especially susceptible due to the high numbers of individuals kept in confined spaces. The disease spreads quickly between animals kept in close contact. The high number of animals in a small area leads to less oxygen in the water and higher levels of waste products, which stress the prawns and make them more susceptible to disease. In farmed prawns WSD kills within two to four days, with death rates of up to 80%. The disease is highly infectious and can be transmitted by live or dead animals and by contaminated water.
The disease was first discovered in China in 1992 and has since spread throughout prawn farming areas of East, Southeast and South Asia, and it appears to have moved from the United States into Central and South America. The spread of the disease can be seen in the White Spot Disease reporting timeline by the World Animal Health Information Database.
Australia was considered free of WSD until an outbreak in December 2016 but it has had an almost constant presence in biosecurity policy, the aquaculture industry and research since the 2000s,