Investigation and analyses of IHHNV-WSSV co-infection in Penaeus vannamei cultured in freshwater and its effects on immune-related enzymes

Abstract:

As white spot syndrome virus(WSSV) and infectious hypodermal and hematopoietic necrosis virus(IHHNV) were both shrimp-infecting viruses and should be reported to the OIE.A follow-up investigation of prevalence of WSSV and IHHNV in P. vannamei cultured in freshwater in Shanghai was carried out in 2014. Results showed that the average single infection rate of WSSV and IHHNV was 42.6% and 38.5% respectively, while co-infection rate of the two viruses was about 20.5%. The prevalence of IHHNV-WSSV co-infection was positively correlated with that of WSSV. Analyses of histopathology and cumulative mortality indicated, although the cumulative mortality of shrimp in the IHHNV-WSSV group was always lower than that in the WSSV group at the same time point, gill tissues of moribund shrimp in the two groups were both damaged seriously, and no significant difference between them was found. The activities of immune-related enzymes(superoxide dismutase and acid phosphatase) demonstrated, compared to the single infection of WSSV, the dual infection of IHHNV and WSSV was able to activate the body's immune system faster and kept the immune response at a higher level during a short period; however, IHHNV-WSSV usually led to an higher and longer immune suppression post activation, which, together with the dual damages caused by IHHNV and WSSV,suggested that co-infection of IHHNV-WSSV would cause greater economic losses than a single infection.