Periodic occurrence of epithelial viral necrosis outbreaks in Penaeus vannamei in Ecuador.

Epizootics of an infectious cuticular epithelial necrosis virus (ICENV) occurred in cultured Penaeus vannamei in Ecuadorian shrimp farms from 1994 to 1996. There were few reports of outbreaks during 1997, but in the second half of 1998 epizootics were again reported. Histopathological examination revealed extensive tissue changes and necrosis as described for infections by what others have called Taura syndrome virus (TSV). Infiltration of haemocytes in the cuticular epithelium was also one of the characteristics in the subacute and acute forms of this disease. Electron microscopy of affected tissues demonstrated the presence of a single type of virus particle in the cytoplasm of diseased shrimps from these outbreaks and it corresponded to the published descriptions for TSV. The epizootics of ICENV were periodic in occurrence, and data indicated that they might be related to the oceanographic and climatic variations reported in the eastern Pacific from 1994 to 1998. Using 3 mo rolling averages, a statistically significant negative correlation was found between prevalence of ICENV and temperature but not temperature change. By contrast, there was a statistically significant positive correlation between prevalence of ICENV and salinity change but not salinity value. Although these data do not establish causal relationships, they suggest that laboratory tests should be conducted to determine whether low temperature and upward changes in salinity can increase shrimp susceptibility to infection and mortality by ICENV.