Experimental infection study reveals differential susceptibilities of Penaeus monodon and Penaeus vannamei to Enterocytozoon hepatopenaei

Enterocytozoon hepatopenaei (EHP) is a significant pathogen affecting penaeid shrimp, particularly farmed whiteleg shrimp Penaeus vannamei, causing hepatopancreatic microsporidiosis (HPM). Although initially reported in tiger shrimp P. monodon, limited data exists on its current impact and pathogenic potential of EHP infection in tiger shrimp due to the shift toward farming P. vannamei. This study aimed to compare the susceptibility of P. monodon and P. vannamei via experimental oral EHP challenge. Challenge group shrimps were fed commercial feed mixed with minced EHP-infected hepatopancreatic tissue (1:1) containing 10⁶ copies/ng DNA for four days, while control groups received commercial pellet feed. Over 90 days, hepatopancreas and fecal samples were aseptically sampled and PCR-tested for EHP presence on days 7, 15, 30, 60, and 90 post-challenge (dpc). EHP loads, quantified using qPCR, were higher in P. vannamei (1.5-5.3 × 10⁵ copies/μL DNA) compared to P. monodon (5.6-10.3 × 10³ copies/μL DNA). Challenged P. monodon tested EHP-positive only in nested step SWP-PCR till 90 dpc. Further, infection was confirmed through wet mount, calcofluor white stain, histology, and in situ hybridization. EHP-challenged P. monodon had a higher survival rate (75 %) than P. vannamei (37.5 %). This first experimental report on EHP in P. monodon indicates it is less susceptible than P. vannamei, suggesting that the reintroduction of P. monodon can help deal with the EHP crisis the shrimp industry is currently going through.