Pathology, isolation, and preliminary molecular characterization of a novel iridovirus from tiger salamanders in Saskatchewan

An iridovirus was confirmed to be the cause of an epizootic in larval and a dult tiger salamanders (Ambystoma tigrinum diaboli) from four separate pond s in southern Saskatchewan (Canada) during the summer of 1997. This organis m also is suspected, based on electron microscopic findings, to be the caus e of mortality of larval tiger salamanders in a pond over 200 km to the nor th during the same year. Salamanders developed a generalized viremia which resulted in various lesions including: necrotizing, vesicular and ulcerativ e dermatitis; gastrointestinal ulceration; and necrosis of hepatic, splenic , renal, lymphoid, and hematopoietic tissues. In cells associated with thes e lesions, large lightly basophilic cytoplasmic inclusions and vacuolated n uclei with marginated chromatin were consistently found. Virus was isolated from tissue homogenates of infected salamanders following inoculation of e pithelioma papilloma cyprini (EPC) cells. The virus, provisionally designat ed Regina ranavirus (RRV), was initially identified as an iridovirus by ele ctron microscopy. Subsequent molecular characterization, including partial sequence analysis of the major capsid protein (MCP) gene, confirmed this as signment and established that RRV was a ranavirus distinct from frog virus 3 (FV3) and other members of the genus Ranavirus. Intraperitoneal inoculati on of 5 x 10(6.23) TCID50 of the field isolate caused mortality in inoculat ed salamanders at 13 days post infection. Field, clinical, and molecular st udies jointly suggest that the etiological agent of recent salamander morta lities is a highly infectious novel ranavirus.