Enterocytozoon hepatopenaei (EHP), amicrosporidian parasite, has emerged as a serious pathogen reported to be
associatedwith 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, we have investigated Penaeus (Litopenaeus) vannamei
cultured in the south-east coast of India for EHP infection using light and scanning electron microscopy, histopathology,
polymerase chain reaction (PCR) and in situ hybridisation. Squash preparation of hepatopancreas
and white faecal strings showed large number of microsporidian spores. Spores under scanning electron microscope
appeared oval and measured 1.7 × 1.0 μm. Histology of infected animals showed severe degeneration of
hepatopancreatic tubules. Basophilic inclusions resembling the developmental stages of EHP were found in the
epithelial cells and large number of spore aggregations was observed in the tubular lumen. Enlargement of
haemal sinuses and encapsulation of hepatopancreatic tubules were also observed in some cases. DNA extracted
fromhepatopancreas was subjected to PCR amplification using primers targetingmicrosporidian ssu rRNA gene.
The PCR yielded an expected product of ~951 bp and the sequences showed 100% identitywith the EHP reported
from Vietnam, Thailand and China. Further screening of field samples was carried out using nested PCR
employing EHP-specific primers. Of the 137 juvenile P. vannamei samples tested, 10 were found to be positive
in the first step and 77 in the nested PCR. Overall prevalence of EHP was estimated to be 63.5%. However, only
first step PCR-positive samples showed discernible number of spores in the hepatopancreas under a lightmicroscope.
Post-larvae of P. vannamei collected from a hatchery were found to be PCR negative for EHP. In situ
hybridisation using EHP-specific DIG-labelled probe showed positive signals in infected hepatopancreatic tissue.
Animals collected from white faeces syndrome (WFS)-affected pond showed higher prevalence of EHP (96.4%)
compared to those from the unaffected pond (39.7%). On the contrary, slow growing animals showed low prevalence
(58.5%) compared to normally growing animals (80.8%). Although EHP could be detected from slowgrowing
as well as WFS-affected animals, the present study could not conclusively elucidate the association of
EHPwith these clinical signs through experimental infection trials. This report forms the first record of the emergence
of EHP infection in cultured SPF P. vannamei in India.
Statement of relevance: E. hepatopenaei (EHP), amicrosporidian parasite, is an emerging pathogen having serious
economic consequences to cultured shrimp in Asia. This report forms the first record of the emergence of the
parasite in farmed P. vannamei fromIndia, and presents a comprehensive account of the pathogen and its impact
on the host.