A haplosporidian parasite associated with high mortality and slow growth in Penaeus (Litopenaeus) vannamei cultured in Indonesia

High mortality of juvenile Penaeus (Litopenaeus) vannamei less than one month old in Indonesia has been observed in shrimp farms and hatcheries since 2007. The gross signs of disease included shrinkage of the hepatopancreas, flaccid bodies, cuticular melanization and retarded growth. Overall loss in the severely-infected farms was 60 to 90% due to progressive mortality. The loss since 2007 is estimated to be more than 5 million US dollars. PCR testing of shrimp samples for major viral pathogens gave negative results, but histopathological analysis of hepatopancreatic (HP) tissue showed evidence of a haplosporidian parasite indicated by cytoplasmic multinucleate plasmodia and trophonts in tubule epithelial cells. Plasmodia caused disruption of HP tubule epithelial cells when they discharged trophonts into the tubular lumen. To confirm the presence of haplosporidia, PCR was performed to amplify a small subunit rRNA gene (SSU rDNA) fragment and a cloned 1.5 kb amplicon showed 96% sequence identity to that of a haplosporidian previously described in P. vannamei from Belize, Central America suggesting that the Indonesian haplosporidian was either conspecific or very closely related. In situ hybridization assays using a probe based on this amplicon gave positive results specifically with the putative haplosporidian lesions. Prevalence of infections in broodstock and ponds from 2004 to 2010 suggested that the haplosporidian disease outbreaks had resulted from stocking of infected post-larvae.

► First report of haplosporidian infections in P. vannamei cultivated in Indonesia
► Histopathology resembled a haplosporidian previously reported from the Americas
► It was confirmed by 96% identity between their small subunit ribosomal RNA genes
► Prevalence of outbreaks decreased after implementation of screening of broodstock.
► Elimination of imported broodstock positive for the haplosporidian is recommended.