Artificial infection of native Korean freshwater shrimp (Macrobrachium nipponense) with white spot syndrome virus (WSSV)

Abstract

The white spot syndrome virus (WSSV) causing the white spot disease (WSD) is an important shrimp pathogen around the world. WSSV has a wide host range and causes up to 100 % mortality in 3-10 days. Because of wide spread of WSSV in nature, it is difficult to find virus free shrimp for researches such as vaccine development. In this study, we used uncultured and Korean native shrimp, Macrobrachium nipponense, for artificial infection of WSSV to use this host-virus combination for future research. M. nipponense was inoculated with WSSV by feeding, cannibalism and injection of purified virus. The mortality was recorded and virus titers in dead M. nipponense were determined by Real-time PCR targeting the WSSV vp28 gene. In feeding test, the first death appeared seven days after inoculation and the final mortality reached 30 % three weeks post inoculation. In cannibalism test, the first death appeared two days post inoculation and the final mortality reached 90 % three weeks after inoculation. In injection test, the mortality was dose dependent. When WSSV inoculums containing 2.0x104 ml/virus particles were injected at 100 µl per 3 g body ratio, the first death appeared one day after inoculation and the final mortality reached 100 % five days post inoculation. Histological observation showed inclusion bodies at gill, antennal gland and other epithelial cells. Typical virus particles were observed form various tissues by electron microscopic observation. Real-time PCR showed increase in virus titer, which indicates virus replication in the inoculated host. All these data indicated that M. nipponense is susceptible to the WSSV, which is reported first time in this species.