Identification of Enterocytozoon hepatopenaei in Mud Crabs (Scylla serrata) Co-infected with White Spot Syndrome Virus in Taiwan

Background: The high mortality rate and stunted growth of marine shrimp in the farm have raised concerns about the outbreak of co-infection involving Enterocytozoon hepatopenaei (EHP) and white spot syndrome virus (WSSV), which could lead to significant economic loss. In a mixed-culture farm consisting of Scylla serrata and Peneaus vannamei located in Yunlin Country, Taiwan, were reported mortality cases on culture animals. Methods: Based on clinical signs, histology and molecular analyses, the disease was diagnosed in this study. In the histopathology examination, infected organs, such as the carapace and gills, were stained with hematoxylin and eosin (H and E), then observed under microscope. For the molecular analysis, SalI DNA fragment (WSSV) and spore wall protein (SWP) gene (EHP) were targeted to detected the pathogen in animal host. Result: The cumulative mortality data for this co-infection indicates that S. serrata (1.5% mortality) exhibits higher susceptibility compared to P. vannamei ( greater than 99% mortality). Phylogenetic tree analysis reveals that the spore wall protein (SWP) gene of EHP and the SalI DNA fragment of WSSV strain extracted from S. serrata are genetically similar to those extracted from Peneaus spp., indicating the potential for cross-species infection. Histopathological examination of lesion tissue observed the presence of WSSV basophilic intranuclear inclusion bodies in the carapace tissue and gill fragments of S. serrata. The source of the disease outbreak is highly suspected to be the feed used, which consisted of raw shrimp and fish. This study provides the first documented case of natural EHP infection with co-infection of WSSV in S. serrata.