Identification of an iridovirus in Acetes erythraeus (Sergestidae) and the development of in situ hybridization and PCR method for its detection

An iridovirus (tentatively named SIV, sergestid iridovirus) that causes high mortality in the sergestid shrimp, Acetes erythraeus, was found in Madagascar in 2004. Severely affected shrimp exhibit a blue–green opalescence. Histological examination revealed massive cytoplasmic inclusions in the cuticular epithelial cells, connective tissues, ovary and testes. The electron microscopic examination showed paracrystalline arrays of virions at a size of 140 nm, suggesting infection with an iridovirus. A pair of PCR primers were selected from the conserved region of the major capsid protein (MCP)-coding sequence among insect iridoviruses and used to amplify a 1.0 kb fragment from the infected A. erythraeus. This fragment was cloned, sequenced and found to be highly similar (upto 80% similarity in translated amino acids with an E value of 1e−124) to the MCP of invertebrate iridoviruses. This clone was then labeled with digoxigenin-11-dUTP and hybridized to tissue sections of infected A. erythraeus, which reacted positively to the probe. The reacting tissues included epithelial cells, connective tissues, and the germinal cells; the same cells as those with inclusions. A PCR method was also developed from the MCP coding sequence for detecting SIV.