Susceptibility of shrimp Penaeus stylirostris to Ecytonucleospora hepatopenaei and horizontal transmission between P. stylirostris and P. vannamei

The microsporidium Ecytonucleospora hepatopenaei (EHP) continues to disrupt farmed shrimp production globally by causing growth retardation, chronic mortality, and enhancing susceptibility to other diseases. While the susceptibility of black tiger shrimp Penaeus monodon and Pacific white shrimp P. vannamei to EHP is well known, the susceptibility of Pacific blue shrimp P. stylirostris to EHP has not been demonstrated. To determine the susceptibility of P. stylirostris to EHP, infectious inoculum was directly injected into the hepatopancreas of specific-pathogen-free (SPF) P. stylirostris. At 17 d post-injection, the developmental stages of the parasite were observed in the EHP-injected P. stylirostris, and EHP was detected by real-time PCR. The EHP-injected P. stylirostris were then divided into 2 groups. In the first group, P. stylirostris (n = 9) were cohabitated with SPF P. vannamei (n = 55), and in the second group, the hepatopancreas was excised from EHP-injected P. stylirostris, homogenized, and fed to SPF P. vannamei (n = 12). Both experimental challenge routes led to the horizontal transmission of EHP from P. stylirostris to P. vannamei, but cohabitation resulted in a stronger infection. In a follow-up study, one group of SPF P. stylirostris was fed EHP-infected P. vannamei tissue, and another group cohabitated with EHP-infected P. vannamei. Both groups of P. stylirostris developed EHP infections. These results clearly provide evidence of both P. stylirostris susceptibility to EHP and the transmission potential of EHP between P. stylirostris and P. vannamei via natural routes such as cohabitation and cannibalism.