The epizootiology of six amphibian mortality events in south central Ontario, Canada, 1999--2002

An epizootic, systemic disease causing death in wood frog (Rana sylvatica) larvae and leopard frog (Rana pipiens) metamorphs at three different locations in Southern Ontario, Canada, has been circumstantially identified as an iridovirus infection. Amphibians affected were found to exhibit hepatic necrosis and basophilic, cytoplasmic inclusion bodies in hepatic tissues. Liver tissue samples were positive for the virus by low level PCR amplification of ranavirus (Family: Iridoviridae ) major capsid protein (MCP) coding region. Positive samples were confirmed by sequence analysis. Clinically normal, laboratory raised wood frog egg broods were also found to test weakly positive for ranavirus. Based on field, histological and molecular investigations, an iridovirus has been identified as a possible cause of a highly infectious viral disease in three Ontario amphibian populations. The effects of this iridovirus pathogen may contribute to declines of amphibian populations in these locations.