Detection and tissue tropism of white spot syndrome baculovirus (WSBV) in captured brooders of Penaeus monodon with a special emphasis on reproductive organs

In cultured shrimp, white spot syndrome 'baculovirus' (WSBV) infection is characterized by a wide range of target tissues, rapid disease onset and high mortality. During the viremic phase of infection, the virus is present in many organs. However, the situation in the natural environment remains unclear. To identify the pattern of the tissue tropism of WSBV infection in adult Penaeus monodon (black tiger shrimp) of wild origin, we conducted a combined study using currently available nucleic acid diagnostic tools and conventional histological observations using light (LM) and transmission electron (TEM) microscopy to examine the sites for virus multiplication. Sixteen parts excised from shrimp specimens were examined: pleopods, gills, stomach, abdominal muscle, hemolymph, midgut, heart, pereiopods, lymphoid organs, integument, nervous tissue, hepatopancreas, testes, ovaries, spermatophores, and eye stalks. All these tissues/organs were found to support WSBV replication. For the first time, in situ hybridization and TEM showed evidence of WSBV in reproductive organs of black tiger shrimp. In testes, WSBV-positive cells were located in the connective tissue layer surrounding the seminiferous tubules and no germ cells were found to be infected. In the spermatophore, only muscle and connective tissue cells were WSBV positive. In the ovary, follicle cells, oogonia, oocytes and connective tissue cells were WSBV positive. However, the fact that we were unable to find any infected mature eggs suggested that infected egg cells were killed by the virus before maturation.