Allan P. Pessier, DVM, DACVP
Amphibian Disease Laboratory, Wildlife Disease Laboratories, Institute for Conservation Research, San Diego Zoo Global, San Diego, CA, USA
Iridoviruses in the genus Ranavirus are large, double-stranded DNA viruses that infect amphibians, fish and reptiles. Although the type species Frog Virus 3 was described in the late 1960s, only in the last 15 yr have ranaviruses been recognized as a significant cause of mass mortality events of wild amphibians and more recently, chelonians. Although Ranavirus infections are not as clearly linked to population declines as another emerging amphibian pathogen, the chytrid fungus Batrachochytrium dendrobatidis, there are ongoing studies and concerns that small, threatened populations may be especially vulnerable to repeated outbreaks of ranaviral disease. There are six officially recognized species of Ranavirus and each species likely has several distinct strains that can vary in virulence and host range. Most amphibian ranaviruses fall into 1 of 3 species groups: the Frog Virus 3-like (FV3) viruses, the Ambystoma tigrinum-like (ATV) viruses and the Bohle iridovirus-like (BIV) viruses. There are a few reports of Ranavirus infection in captive amphibians; however, the prevalence and significance to zoo collections are unknown because of an overlap of clinical and pathologic findings with other infectious diseases and a lack of well-validated antemortem tests. Although Ranavirus infections are relatively easily diagnosed by molecular diagnostic testing (e.g., PCR) in sick animals with high viral loads, the ability to reliably detect subclinical infections using tissue samples, oropharyngeal swabs or cloacal swabs is debatable. Complicating disease risk assessments for amphibian translocation and reintroduction programs is the detection of subclinical infections during disease surveillance efforts without an efficient method to distinguish between different ranaviral strains. Treatment of sick animals is largely supportive, but early studies suggest that environmental temperature elevation may be helpful in some cases.