Isolation of a lethal virus from the endangered tiger salamander Ambystoma tigrinum stebbinsi

The Sonora tiger salamander Ambystoma tigrin um stebbinsi Lowe is a genetically distinct race restricted to about 30 small ponds in the San Rafael Valley in southern Arizona, USA, which was added recently to the USA Federal List of Endangered Species. Populations of these salamanders periodically experience decimating epizootics. Virus was isolated from diseased salamanders using fish cell cultures, injected into healthy laboratory-reared salamanders, and then reisolated in cell culture. Electron microscopy of thin sections from dying salamanders revealed abundant enveloped and nonenveloped icosahedral virus particles approximately 160 to 180 nm in diameter in the cytoplasm of skin and liver cells and free in the intercellular spaces. This virus, believed to be an iridovirus based on viral morphology and host pathology, was demonstrated to be the primary pathogen in these epizootics, and is the first lethal epizootic virus reported from salamanders. We have named the virus Ambystoma tigrinum Virus (ATV). Hemolytic bacteria were isolated from sick individuals, but we were unable to induce the disease by exposing salamanders to isolated bacteria at concentrations up to 10(8) ml(-1).