Studies on transmission of white spot syndrome associated baculovirus (WSBV) in Penaeus monodon and P. japonicus via waterborne contact and oral ingestion

WSBV (white spot syndrome associated baculovirus) is considered to be the main causative agent of a recently reported disease which has resulted in serious mortality among cultured penaeid shrimp in Taiwan and is characterized by obvious white spots on the body. Shrimp infectivity tests of WSBV were carried out by means of waterborne contact and oral ingestion. Healthy juvenile P. monodon and P. japonicus and healthy P. penicillatus postlarvae were immersed in filtrates prepared from either diseased P. japonicus or diseased P. monodon, both of which exhibited marked white spot signs. Cumulative mortalities of the three tested shrimp species reached 100% within 4–6 days. Using PCR with a specific primer set, WSBV was first detected in the previously healthy P. monodon immersed in filtrate from diseased P. monodon 6 h postinoculation (h p.i.). At 24 h p.i. detection rates reached 90%, and even though the tested shrimp failed to show visible evidence of disease, they nonetheless suffered 33% mortality. The appearance of WSBV in experimentally infected P. penicillatus postlarvae was detected at 24 h p.i. and reached 100% by 72 h p.i. Healthy P. monodon fed with diseased P. japonicus as well as those fed with diseased P. monodon became 80–90% WSBV-positive 24 h p.i. by PCR and all of the tested shrimp died within 5 d. Obvious white spots appeared on the exoskeleton of shrimp whether they were infected by waterborne contact or orally. WSBV was found highly pathogenic to the three tested shrimp species and was readily transmitted across different penaeid shrimp.