Hepatopancreatic microsporidiosis (HPM) caused by a microsporidium, Enterocytozoon hepatopenaei (EHP) is currently one of the major pathogens of penaeid shrimp that is causing enormous losses in shrimp production in Asia. Recently, the disease has been reported from Venezuela as well in the western hemisphere. One of the limitations in developing HPM resistant line of shrimp is the lack of a robust and reproducible laboratory experimental challenge method that could be used for screening genetic lines of penaeid shrimp.
Herein, we report an E. hepatopenaei experimental challenge model using two S pecific P athogen F ree (SPF) Penaeus vannamei shrimp lines originating from different geographic locations. The shrimp (weight range 6.0 to 7.0 g ) from each population were tagged with a unique elastomer tag, maintained in the same tank before exposing to fecal strings from known EHP-infected shrimp as inoculum. Fecal strings were collected daily by siphoning from one 1000 L tank containing 60 EHP-infected shrimp. Histopathology and r eal-time PCR assays were conducted for confirmation of EHP infection in the challenged animals . The final survival was equivalent in both population (i.e. ~90%), b ut the prevalence of EHP varied between the two populations. SPF1 had significantly higher growth than SFF2 line (for both EHP-challenged and unchallenged treatments tanks).
Histopathology revealed typical EHP lesions in both challenged groups. Real-time PCR data showed prevalence of EHP at 77% and 52 % in SPF 1 and SPF2 , respectively. Considering the shrimp from SPF1 and SPF2 were maintained and experimentally challenged under the same tank environment, the difference in the severity of infection observed in these two groups is likely due to the inherent genetic background. The data suggest that experimental challenge using fecal string as an inoculum source w ould be a viable approach in screening for EHP resistance in penaeid shrimp and in developing therapeutics/ functional feed against EHP.