Investigation Of The Co-infection Of IHHNV And WSSV In Wild And Cultured Shrimp And Its Effects On Penaeus Vannamei

In order to understand the prevalence of co-infection of IHHNV and WSSV in the case of wild and farmed shrimp,wild samples from the coast of Jiangsu, Zhejiang and Shanghai was collected for the 2 virus detection during May in 2013 to August in 2014,A follow-up investigation in cultured shrimps was also carried out for the detection of IHHNV and WSSV during May to September in 2014. The results showed that average prevalence of WSSV and IHHNV was 21.38% and 19.20% respectively, in the wild samples from the coast of Jiangsu, Zhejiang and Shanghai, and the co-infection rate was 6.88%; by contrast, high prevalence of the 2 viruses was still existed, and the average detection rate of the WSSV and IHHNV was 42.6% and 38.5% respectively, and the co-infection rate of IHHNV-WSSV was up to 20.5%, the result also showed that co-infection rate of the 2 viruses was positively correlated with the prevalence of WSSV.In this study IHHNV was first detected in wild P. penicillatus, which was named PPD1301. By T/A cloning and sequencing methods, a complete c DNA genomic sequence consisting of 3603 bases was assembled, the complete c DNA genomic sequence had a high similarity among nucleotide sequences(>99.31%) with those previously reported from America and Asia, while gave a very low similarity of 86.12% with type 3A from Madagascar(DQ228358) and 91.95 % with type 3B from Tanzania(AY124937); homologous analysis showed that present PPD1301 was phylogenetically more closely related to the isolates from America and Asia.In recent years, reports about co-infection of IHHNV and WSSV was becoming popular, although it has been reported that shrimp pre-infected with IHHNV was resistant to WSSV, persistence of IHHNV may block the entry of WSSV by mechanism of down-regulation of viral receptors or by competition for receptor binding, while studies about effects of shrimps co-infected with IHHNV and WSSV was none. In this study, P. vannamei was used as test animals to explore the pathogenicity and immune-related enzymes—superoxide dismutase(SOD) and acid phosphatase(ACP) of the shrimp co-infected with IHHNV and WSSV. Cumulative mortality analysis showed that, in both the IHHNV and WSSV co-infected group and WSSV single infected group, the cumulative mortality rate were increased with the time,cumulative mortality of WSSV single infected group was always higher than IHHNV and WSSV co-infected group, 144 h after WSSV infection, mortality rate of WSSV single infected group(83.3% ± 6.8%) is about 1.3 times of IHHNV and WSSV co-infected group(62.5% ± 3.4%); Pathological analysis showed, 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 demonstrated, compared to the single infection of WSSV, the dual infection of IHHNV-WSSV was able to activate the body’s immune response faster and kept the immune response at a higher level during a short period, however, IHHNV and WSSV co-infection usually led to a longer immune suppression post activation. Together with the damages caused by IHHNV and WSSV, co-infection of IHHNV-WSSV would cause larger economic losses than a single infection.In conclusion, IHHNV and WSSV single infection and co-infection was existed in wild shrimp samples collected from the coast of Jiangsu, Zhejiang and Shanghai,the co-infection prevalence was low(6.88%), while the IHHNV was first found in wild P. penicillatus and this IHHNV isolates was infectious, which was phylogenetically more closely related to the isolates from America and Asia. Single and co-infection was popular in cultured shrimp and was positively related with the prevalence of WSSV. The study showed that co-infection of IHHNV and WSSV could lead to greater economic losses in shrimp farming,which would provide helpful data for the shrimp farming.