Study on the Pathogenesis of the White Spot Syndrome Virus (WSSV) on Juvenile Penaeus monodon in Vietnam

The white spot syndrome virus (WSSV) causes disease and mortality in cultured and wild Penaeus monodon. In this study, specific pathogen-free P. monodon were injected with WSSV to determine in which primary organs the virus replicates and to analyze viral spread. Shrimps were injected with a low SID50 endpoint (shrimp infectious dose resulting in 50% infected shrimp) of 101.5 or a high SID50 of 104 of the virus. Six shrimps per treatment were collected at 0, 3, 6, 9, 12, 15, 18, 21, 24, 30, 36, 42, 48, 54, and 60 h post injection (hpi) for detection of the virus in tissues from 10 organs by immunohistochemistry. In shrimps injected with the low dose, WSSVinfected cells were first detected in the heart and antennal gland 12 hpi, then in the foregut, stomach, and gills at 18 hpi. The integument was infected 24 hpi and the hematopoietic tissue, lymphoid organ, midgut, and connective tissues 36 hpi. In shrimps that received the high dose, the heart, antennal gland, stomach, gill, and connective and hematopoietic tissues were WSSV-positive 12-15 hpi while the foregut and cuticular epithelium were positive 18 hpi and the lymphoid organ and midgut were positive 21 hpi. The present study confirmed the replication of WSSV in P. monodon heart, antennal gland, foregut, stomach, gills, cuticular epithelium, hematopoietic tissue, connective tissue, and lymphoid organ.