Case Study: White Spot Syndrome Virus
White Spot Disease (WSD) is a pandemic disease of crustaceans caused by White Spot Syndrome Virus (WSSV). The virus first appeared in China in the early 1990s followed by spread to other major aquaculture regions of the world including Southeast Asia, the Americas, India, the Middle East and Europe. Serious production losses (90- 100% mortality) occur with 3 – 10 days of WSD incidence and the total economic damage caused to the shrimp aquaculture industry has been estimated at $8–$15 billion, increasing by $1 billion annually.
Clinical signs of WSSV infection include reduced food consumption, lethargy, loosening of the cuticle and often reddish discolouration. The presence of white spots of 0.5 to 2.0 mm in diameter on the exoskeleton and appendages are diagnostic of the disease in most, but not all, host species. Currently there are no effective treatments for this disease. Various management practices and biosecurity measures are currently employed to control outbreaks. These range from basic hygiene measure such as removal of bottom sludge, liming and disinfection before stocking, to inoculation with inactivated WSSV or recombinant viral proteins and the use of pathogen free/pathogen resistant brood stock. They are limited though by practicalities and affordability both for application on a commercial scale and for rural small-scale farms. The best methods for preventing losses is the exclusion of the virus from production systems or the avoidance of environmental conditions which induce host stress, stimulate viral replication or facilitate viral transmission.
Sources: Verbruggen et al 2016, Karim et al 2011