Abstract
Hepatopancreatic microsporidiosis caused by Enterocytozoon hepatopenaei (EHP) causes substantial economic losses to the shrimp farming industry. Despite the wide potential host range, most research on EHP was focused on Penaeus vannamei due to its widespread farming and severe growth retardation. However, there needs to be more available information on EHP infection in farmed tiger shrimp, P. monodon, especially considering its re-introduction and use of specific pathogen-free (SPF) seeds in India. A polymerase chain reaction-based (two-step PCR) survey was conducted to understand the prevalence of EHP in P. monodon farms across six states in India. Two different PCR assays, one specific to the spore wall protein (SWP) gene and the other targeting the SSU rRNA gene. While only 19 of 63 farms (30.15%) surveyed during the study revealed the presence of EHP using SWP-specific PCR, 38 farms (60.31%) were found to be positive with SSU rRNA PCR. However, only one of the farms showed EHP in the first step of PCR. The low level of infection, as indicated by the PCR analysis, was further validated and confirmed by histology and quantitative real-time PCR (qPCR). The EHP load ranged from 1.0 × 103 to 3.7 × 106 copies/ µg DNA, and histology of hepatopancreas showed only mild pathological changes and inclusion-like bodies similar to the developmental stages of EHP. Some of the samples showed bacteria-induced haemocyte infiltration and nodule formation. However, no microsporidian spores could be noticed in the histological sections. EHP SWP-specific PCR amplicons were sequenced, and phylogenetic analysis of the sequences showed similarity with earlier reported EHP strains from P. vannamei from Thailand, Latin America and India. A statistical epidemiological study to identify risk factors associated with EHP infection revealed that the presence of EHP infection in previous cultures, the use of wild seeds and continuous farming as potential risk factors and the use of SPF seeds and bleaching as protective factors. P. monodon is susceptible to EHP infection, yet the impact on the species is significantly lower than that reported in P. vannamei. The present report forms the latest report on the prevalence of EHP in P. monodon farms in India.