Chapter 16 - White spot syndrome virus in wild mud crabs

Abstract

Generally, the viral disease which usually affects Scylla spp. is the white spot syndrome virus (WSSV). WSSV was discovered in 1992 in Southeast Asia and has become one of the most serious viral pathogens. WSSV was first detected in Fujian province, China, in 1992 and has spread to many major shrimp farming regions in South-East Asia, East-Asia, India, Latin America, Europe, and Middle East. WSSV is classified within the genus Whispovirus. WSSV infections in many of the nondecapod host are latent infections with no apparent pathology to the host species. In natural and experimental challenges, the gross signs of moribund WSSV-infected mud crabs include weakness, lethargy, reduced feed consumption, and detachment of legs. In experimental challenges in mud crabs, the histology revealed enlarged basophilic nuclei in normal WSSV-target tissues such as the subcuticular epidermis and gills, cell degeneration, and basophilic intranuclear inclusions. Studies have shown that β-actin and myosin-9 play an important role in the immune response to WSSV. WSSV is mainly transmitted via horizontal routes of infection, such as exposure to infected water, ingestion of dead/moribund carrier, and ingestion of dead/moribund vector. Several cell cultures from crabs have been developed for WSSV including hepatopancreas, hemocytes, testis, and hematopoietic tissue. Immunodiagnostic and molecular methods are available for the detection of WSSV. Vaccines and biosecurity measures are among the WSSV disease control measures available so far.