Primary diagnosis and surveillance of white spot syndrome virus in wild and farmed crawfish (Procambarus clarkii, P. zonangulus) in Louisiana, USA

This is the first report of natural white spot syndrome virus (WSSV) infection in wild and large-scale farmed crawfish. In the spring of 2007, 3 crawfish farms experienced heavy mortality in ponds populated by Procambarus clarkii and P. zonangulus. Histological examination revealed findings consistent with severe viral infection characterized by numerous intranuclear inclusions in ectodermal and mesodermal tissues. Samples tested by in situ hybridization, injection bioassay in Litopenaeus vannamei, and PCR (nested and real time) were all positive for WSSV. Samples were sent to the National Veterinary Services Laboratory in Ames, Iowa, USA, where WSSV was verified. Subsequently, a multi-parish survey of 184 sites in Louisiana (including farm and wild basin samples) using real-time PCR determined that >60% of sites sampled were positive for WSSV, including wild basin samples.