Transmission of White Spot Syndrome Virus (WSSV) through Bivalve Mollusk (Meretrix meretrix) and Microalgae (Chlorella spp.)

Abstract White Spot Syndrome Virus (WSSV) is the most virulent viral pathogen, which causes severe economic losses to the shrimp culture industry. The major obstacle in the control and prevention of WSSV is its broad host range and wide geographical distribution. WSSV transmission can occur via hosts in which the virus is amplified (active hosts) or through hosts in which the viral DNA just accumulates (carrier or passive host). The bivalve mollusk Meretrix meretrix is routinely used as live feed for shrimp brooders, and occasionally co-cultured with shrimp in culture ponds. Earlier study showed virus can efficiently trapped by bivalve mollusks due to their filter feeding mechanisms. The microalgae play an important role in nutrition of shrimp larval cycle. There is no proper study on WSSV accumulation and their replication in mollusks and microalgae. The objective of this study was to evaluate the role of bivalve mollusk ( Meretrix meretrix ) and microalgae ( Chlorella spp ) as a vector in WSSV transmission. Clams and shrimp were reared in WSSV spiked water and examined for the WSSV accumulation. Clam gill were tested negative initially for two days and become nested PCR positive after 6th day and progressed as first step positive after 8th day of introduction in to the WSSV spiked sea water. The infection of WSSV in clam were confirmed by PCR, histopathology and in-situ DNA hybridization assay. WSSV was spiked in Chlorella culture @ 1000 WSSV mL − 1 of Chlorella cells. The Chlorella WSSV mixture at different time duration from 1 to 10 days were co cultured along with protozoae and the mortality was monitored. Dead and moribund protozoae were regularly collected and screened for WSSV infection by PCR. Shrimp larval mortality was observed from day one to six days, and there was no mortality of protozoae from the seventh day to the tenth day. These results revealed that Chlorella spp can carry WSSV for six days in the condition of 1000 WSSVmL − 1 of Chlorella cells. The results of this study indicated that the bivalve mollusks may filter and accumulate WSSV from water column and might prevent horizontal transmission pathway of WSSV and microalgae could carry WSSV and infect shrimp larva. These observations may imply that clam and chlorella were potential carriers of WSSV.