Enterocytozoon hepatopenaei (EHP) is a risk factor for acute hepatopancreatic necrosis disease (AHPND) and septic hepatopancreatic necrosis (SHPN) in the Pacific white shrimp Penaeus vannamei

The hepatopancreatic microsporidian Enterocytozoon hepatopenaei (EHP) is an emerging pathogen that affects cultured shrimp Penaeus vannamei in several SE Asian countries including China, Vietnam, Thailand, Indonesia, India and Malaysia. EHP infections are often accompanied by opportunistic infections of Vibrio spp. Laboratory challenges and a case control study were used to determine the effects of EHP infection on two Vibrio diseases: acute hepatopancreatic necrosis disease (AHPND) and septic hepatopancreatic necrosis (SHPN). To determine the effect of EHP on AHPND, two independent experimental infections were carried out. EHP-infected shrimp (EHP-AHPND group) and healthy shrimp (AHPND group) were challenged with 2.4 × 10⁵ CFU/mL of AHPND-causing Vibrio parahaemolyticus. The results of the experimental infections showed that EHP-AHPND group exhibited higher mortalities (60 and 44%) than the AHPND group (0 and 18%). The pathological effects of AHPND vs. EHP-AHPND groups were compared during the first 12 h post infection, 57% of the EHP-AHPND group displayed severe hepatopancreas necrosis and sloughing, features characteristic of AHPND infection while only 11% of AHPND group showed these features. This indicated that EHP-infected shrimp have a higher susceptibility to AHPND infection. To determine the effect of EHP on SHPN, we reviewed the histopathology of samples collected where EHP is endemic; and a case control study was carried out to determine the association between SHPN and EHP. We compared individual shrimp displaying histological signs of SHPN with the shrimp from the same ponds without these signs. A strong association was found between SHPN and EHP, indicating that shrimp with EHP have an increased susceptibility to SHPN. These findings suggested that EHP infection is a risk factor for both AHPND and SHPN.