A comparison of the severity of white spot disease in cultured shrimp (Fenneropenaeus indicus) at a farm level in Egypt. I-Molecular, histopathological and field observations

Since 2009, white spot syndrome virus (WSSV) has been detected in cultured shrimp Fenneropenaeus indicus and caused severe mortalities in cultured penaeid shrimp in Egypt. The results showed that the variation of WSSV loads was correlated with DO, temperature and ammonia-N concentrations (NH₄). These results suggested that maintaining high level DO, high water temperature and low level of ammonia might prevent the diseases outbreak and mortality.  This study investigated the occurrence of WSD in cultured F. indicus in shrimp farms of Egypt using H&E histopathology and PCR examinations. F. indicus shrimps obtained from ponds experiencing no WSD outbreaks (ISHNO) and ponds experiencing outbreaks (MMWO) showed typical clinical signs of WSD. The results of morphometrics showed no difference between ISHNO and MMWO and the WSSV does not affect the growth or body shape of the shrimp. Overall, the histopathological changes in the tissues of the shrimp from ISHNO and MMWO ponds were similar but the severity of changes was more in MMWO compared to ISHNO. A total of 16 Haemolymph and 22 gill tissues were collected from ISHNO and MMWO were tested by PCR. The samples were all tested positive for WSSV by IQ2000 WSSV DPS. The MMWO shrimp samples appear to have stronger band intensity compared to the ISHNO, this explains why MMWO experienced mortalities earlier time than ISHNO. There were differences in the number and percentage of infected shrimp between female and male in both ISHNO and MMWO. In ISHNO farms, 2047 (68.23%) female and 953 male (31.76%) infected by WSSV. In MMWO farms, 2078 (69.26%) female and 922 (30.73%) male infected by WSSV. The effect of WSSV was not significant on the growth rate and survival during production cyscle. However, mortality occurs at a certain point of time and affects the whole ponds. This was clear where massive mortalities occurred earlier in MMWO than ISHNO after 16 weeks (day 112) of culture.