The disease was first reported in farmed shrimp in Thailand and then China in 1992-93. In 1995, it was reported in shrimp farms located in south Texas and in South Carolina. In 2004, it was confirmed in a shrimp farm in Hawaii. It is called “white spot syndrome” because in infected shrimp white spots develop in the shell. WSSV was found in wild shrimp and crabs off-shore in the Gulf of Mexico and near shore in Texas, Mississippi, Georgia and South Carolina during 1999-2002.

1. Feeding infected shrimp or using them as bait in crawfish traps.
2. Introducing infected crawfish (trapped from an infected pond or wild marshland) as stock into the pond.
3. Shorebirds carrying infected crawfish from one place or the other and possibly regurgitating infected crawfish before digesting them.
4. Infected crawfish migrating from one pond to another.
5. Moving contaminated equipment (traps, boats, etc.) from an infected location to a clean pond.
6. People carrying the virus from one place to another on their boots or personal equipment. 
7. This disease cannot be spread by bird feces. No viable WSSV virus was found following passage through the gut of either sea gulls or chickens.

At this point no one can say with any certainty. There are many possibilities. Many countries export both pond-raised and wild shrimp to the United States. A study of imported shrimp indicates occurrence of WSSV may be very high in these products. For example, in one study 10 different lots of imported frozen shrimp tails were screened for WSSV. In eight of 10 samples tested, WSSV was detected. Live shrimp were then exposed to these WSSV- positive tissues either as food or by injection. WSSV resulted in 100% mortality in the indicator shrimp in four of nine tests. The results of the study indicated that the virus was infectious to previously healthy live shrimp either by ingestion or by injection. Another recent study suggested an appreciable proportion of the shrimp sold in Massachusetts' supermarkets are carrying WSSV, and this constitutes a substantial risk of importation of this virus into the local environment. Effluents or solid waste from re-packing contaminated shrimp could create a risk of virus transmission to susceptible species and carriers in the natural environment.

Imported frozen shrimp used as bait for coastal fishing is also a hazard. Leftover bait shrimp that is discarded could be picked up by wild shrimp or crabs, thereby creating immediate risks for those populations and spread to others. The same risk to wild crawfish exists when frozen imported shrimp are used for bait in inland waters. WSSV is highly infectious for most known species of marine shrimp, and natural infections also occur in many species of crabs, lobsters and prawns and other crustaceans, although they often are not lethal. Shrimp stocked with infected carriers acquire active infections within 36-48 hours.

More than 40 known species of crustaceans have been documented to carry the disease. Many more are probably capable of becoming carriers if exposed. Even some aquatic insects have been shown to carry the virus, and several species of crabs and shrimp in the wild have been found infected with the virus without displaying any of the clinical signs, acting as a continual reservoir of infection. Whether shrimp or crawfish, once wild crustaceans are infected, they can serve as a source of the disease for farmed animals, and infected farms can in turn release the disease back into the environment.