Ambystoma opacum die-off in Great Smokey Mountains National Park (Photo: Matt Niemiller)

Ambystoma opacum die-off in Great Smokey Mountains National Park (Photo: Matt Niemiller)

Ranavirus Info

Note: The new edited volume, Ranaviruses: Lethal viruses of ectothermic vertebrates, which provides thorough reviews on each of these topics and more, is now available here.

Distribution & Conservation

Ranaviruses have a truly global distribution. For instance, ranaviruses are known to infect at least 91 amphibian species in 14 families from North and South America, Europe, Asia, Australia, and, very recently, Africa. Similarly ranaviruses have been identified in aquaculture and in wild fishes in North America, Europe, Asia, and Australia. Several studies have found ranavirus-infected animals in the international commercial trade of amphibians, reptiles, and fishes. Overall ranavirus has been found in at least 173 ectothermic vertebrates from at least 32 nations around the world.

Ranaviruses are now considered a ‘Notifiable Pathogen’ by the OIE (the World Organization for Animal Health) and so must be reported to this organization by member countries. The GRC is developing a Global Ranavirus Reporting System (GRRS) in conjunction with the US Forest Service, Southeast Partners in Amphibian and Reptile Conservation (SEPARC), and the EcoHealth Alliance.

European Common Frog Rana temporaria (Photo: Richard Bartz, Wikimedia commons)

Populations of the European common frog, Rana temporaria, have declined with the emergence of ranaviruses in England. (Photo: Richard Bartz, Wikimedia commons)

Because of their broad distribution, large host range, and often high virulence, ranaviruses have the potential to be important threats to some amphibians, fishes, and reptiles. In the United Kingdom, for instance, a ranavirus has been associated with widespread declines of the common frog, Rana temporaria, and frequent die-offs in other amphibians may be associated with local extirpation.  Ranavirus-associated die-offs have been observed in populations of Eastern Box Turtles (Terrapene carolina carolina) in several areas in the eastern United states. Turtles often require many years to reach sexual maturity and have little recruitment in any given year. These life history traits are offset by normally very high adult survival. Turtles may be poorly equipped to buffer large ranavirus epidemics in adults like those seen in recent years.

For more information see:

  • Gray, M. J., D. L. Miller, and J. T. Hoverman. 2009. Ecology and pathology of amphibian ranaviruses. Diseases of Aquatic Organisms 87:243-266.
  • Miller, D., M. Gray, and A. Storfer. 2011. Ecopathology of ranaviruses infecting amphibians. Viruses 3:2351-2373.
  • Schloegel, L. M., P. Daszak, A. A. Cunningham, R. Speare, and B. Hill. 2010. Two amphibian diseases, chytridiomycosis and ranaviral disease, are now globally notifiable to the world organization for animal health (OIE): An assessment. Diseases of Aquatic Organisms 92:101-108.

Ecology & Evolution

Ranaviruses are transmitted by direct contact, through the water, and by consuming infected tissues or fomites. The duration and outcome of ranavirus infection varies among host species, developmental stage, and temperature and probably many other environmental factors. In amphibians, most mortality events have been associated with larvae (tadpoles) at breeding sites, with larvae generally being more susceptible than adults. It is not known whether this pattern holds in fish and reptiles.

Bullfrog tadpole

American bullfrog (Rana catesbeiana) tadpole in Georgia, USA with a possible ranavirus infection. (Photo: Alan Cressler)

Several studies have found that amphibians exposed to anthropogenic “stressors,” such as herbicides and insecticides or even cattle access to a pond can make individuals more susceptible to ranaviruses or epidemics more severe. However natural “stressors,” such as the presence of aquatic predators, do not appear to have similar effects on susceptibility. Importantly, ranaviruses are not universally lethal, even in highly susceptible species and stages. Low-level, sublethal infections appear to be common in at least some taxa. This may help explain how ranaviruses persist between outbreaks, although persistence outside the host in the environment has not been entirely ruled out. The evolutionary history of ranaviruses is currently being worked out, but it seems that there have been at least a couple of “jumps” from one host taxa to another (e.g., fish to frogs). There is also evidence of local coevolution between tiger salamanders in western North America and their viruses.

For more information see:

  • Gahl, M. K., and A. J. K. Calhoun. 2010. The role of multiple stressors in ranavirus-caused amphibian mortalities in Acadia national park wetlands. Canadian Journal of Zoology 88:108-121.
  • Gray, M. J., D. L. Miller, and J. T. Hoverman. 2009. Ecology and pathology of amphibian ranaviruses. Diseases of Aquatic Organisms 87:243-266.
  • Hoverman, J. T., M. J. Gray, N. A. Haislip, and D. L. Miller. 2011. Phylogeny, life history, and ecology contribute to differences in amphibian susceptibility to ranaviruses. EcoHealth 8:301-319.
  • Jancovich, J. K., M. Bremont, J. W. Touchman, and B. L. Jacobs. 2010. Evidence for multiple recent host species shifts among the ranaviruses (family Iridoviridae). Journal of Virology 84:2636-2647.
  • Miller, D., M. Gray, and A. Storfer. 2011. Ecopathology of ranaviruses infecting amphibians. Viruses 3:2351-2373.
  • Reeve, B. C., E. J. Crespi, C. M. Whipps, and J. L. Brunner. 2013. Natural stressors and ranavirus susceptibility in larval wood frogs (_Rana sylvatica_). EcoHealth 10:190-200.

Virology & Immunology

Ranaviruses are large, double-stranded DNA viruses. Their ~150 nm, icosahedral capsid can be seen in the cytoplasm of infected cells with electron microscopy, often in paracrystaline arrays. Their ~105 kbp genome, which encodes ~100 genes, comprises a single linear, but circularly permuted, element. The unique replication cycle of ranaviruses (and the other vertebrate iridoviruses) involves both nuclear and cellular phases, which results in a plasmalipid envelope, which is derived from the nuclear membrane, internal to the protein capsid. The capsid may be enveloped, if it buds from the host cell membrane, or naked if the host cell lyses.

Iridovirus vision (Credit: ViralZone 2009, Swiss Institute of Bioinformatics)

Iridovirus virion (Credit: ViralZone 2009, Swiss Institute of Bioinformatics)

For more information see:

  • Chen, G., and J. Robert. 2011. Antiviral immunity in amphibians. Viruses 3:2065-2086.
  • Chinchar VG (2002) Ranaviruses (family Iridoviridae): Emerging cold-blooded killers. Archives of Virology 147:447–470.
  • Whittington, R. J., J. A. Becker, and M. M. Dennis. 2010. Iridovirus infections in finfish — critical review with emphasis on ranaviruses. Journal of Fish Diseases 33:95-122.
  • Williams, T., V. Barbosa-Solomieu, and V. G. Chinchar. 2005. A decade of advances in iridovirus research. Advances in Virus Research 65:173-248.