HISTOPATHOLOGY AND IN SITU DETECTION OF THE MICROSPORIDIAN Enterocytozoon hepatopenaei (EHP) IN Penaeus vannamei CULTURED IN A LATIN AMERICA COUNTRY

EHP is an intracellular, spore-forming parasite that has become a critical threat to the shrimp farming industry in SE Asia. This parasite replicates within the cytoplasmic area of the tubule epithelial cells in the hepatopancreas, and infected shrimp exhibit reduced feeding and severely retarded growth. In this study, we describe the first case of EHP-infected Penaeus vannamei cultured in Latin America. Its histopathology is very similar to that of SE-Asia EHP, with infected shrimp showing basophilic inclusions in tissue of the hepatopancreas. Upon in situ hybridization of an 18S rRNA gene fragment labeled with digoxigenin to the infected P. vannamei tissue, the probe reacted intensely to the basophilic inclusions within the cytoplasm. We also compared the sequence similarity in 18S rRNA gene (1.1 kb) and in spore wall protein gene (partial gene, 457 bp) between SE Asia and the Latin America isolates; and the result showed 99% and 91% identities, respectively. This suggests that this Latin America EHP is a unique isolate, and not a recently introduced isolate from SE Asia. The emergence of EHP in the western hemisphere will have a significant impact on the shrimp production if it spreads to other farms within the region. As infection with EHP at early stages does not exhibit obvious clinical signs and the spores can persist in the environment, the potential for the rapid spread of this parasite is high. Therefore, the shrimp cultured within the region should be monitored closely for the presence of EHP.