Detection and molecular characterization of the Microsporidian parasites in cultured Shrimp

Abstract

Microsporidian parasite has emerged as a serious pathogen reported to be associated with retarded growth in cultured shrimp in many of the shrimp growing countries in Asia. As a part of ongoing disease surveillance among the farmed shrimp, this study investigated black tiger shrimp (Penaeus monodon) culturing in the south-west region especially Satkhira and Bagherhat district of Bangladesh for the prevalence of microsporidian parasite using light and scanning electron microscopy, histopathology and polymerase chain reaction (PCR). The evolutionary history among parasiteswere inferred using the Neighbor-Joining method. The optimal tree with the sum of branch length = 0.21208716 was shown. Evolutionary analyses were conducted in MEGA7. Squash preparation of hepatopancreas and stomach showed large number of microsporidian spores under light microscopy. Spores under scanning electron microscope appeared oval shapes. Histology of infected animals showed severe degeneration of hepatopancreatic tubules. Early and late stage of microsporidian parasites in hepatopancreatic tubules were also observed in some cases. Morphological dissimilarities among the parasites also observed. DNA extracted from hepatopancreas was subjected to PCR amplification using primers targeting microsporidian SSU rRNA gene. The PCR yielded an expected product of ~328 bp and the sequences showed 83% identity with the Paranucleospora theridion (GenBank no. FJ594971.1) reported from Vietnam, Thailand and China. Further screening of field samples was carried out using EHP-specific primers. Out of 10 P. monodon samples tested, none found to be positive. So the prevalence of EHP was not estimated. To understand the microsporidian parasite Enterocytozoon hepatopenaei (EHP) prevalence, samples should be drawn from more shrimp farms with information about their management strategies. This is the first report identifying microsporidian parasites in cultured shrimp farm along the South-west region especially Satkhira and Bagherhat district in Bangladesh.