Multiple infections of Entrerocytozoon hepatopenaei and Hepatopancreatic parvovirus in pond-reared Penaeus vannamei in India

Outbreaks of infectious disease affecting Penaeus vannamei (Pacific white shrimp), the most commonly cultured shrimp species in India, has led to severe economic loss. Five randomly selected P. vannamei samples were collected from 154 grow-out ponds located at Cuddalore and Nagapattinam Districts in Tamil Nadu where shrimp showed severe growth retardation over a two-year period. In addition to growth retardation, affected shrimp displayed an atrophied hepatopancreas (HP) and a white/empty gut and stomach. Histopathology revealed the various developmental stages (plasmodia to mature spores) of massive acidophilic microsporidian spores in the cytoplasm of hepatopancreatic (HP) tubule cells. Some of the microsporidian-infected shrimp also showed distinct hypertrophied nuclei within the HP tubular epithelial cells. TEM revealed different growth stages (meront to mature spores) of intracytoplasmic microsporidian parasites as well as icosahedral viral-like particles (VLP) ranging in diameter from 22 to 24 nm in the cytoplasm and nucleus of HP tubular epithelial cells and extracellular spaces. Among the pooled (five shrimp from each farm) HP samples from 154 farms, 53 (34.4%) farms were identified to be PCR-positive for Enterocytozoon hepatopenaei (EHP), whereas 11 (7.1%) were identified to be PCR-positive for Hepatopancreatic parvovirus (HPV). Among the PCR positives, eight (5.2%) farms were found to be positive for both EHP and HPV, indicating that some P. vannamei had dual infections with EHP and HPV. This is the first such report on the simultaneous occurrence of dual infections caused by EHP and HPV.