Ranaviruses: Another blow for amphibians worldwide

In my last post I mentioned the shortage of frogs in my usual amphibian hotspot and I wondered if ranavirus might be to blame. I realized that I didn’t know much about this disease–particularly about its effects in Virginia–so I decided to do some research on the subject.

Ranavirus? Haven’t amphibians suffered enough?!

Alas, no; evidently ranaviruses are a thing and they’re not going away anytime soon. So what is a ranavirus? Put simply, it is one of many similar types of viruses that can infect frog and salamander populations. Ranaviruses (or just “ranavirus” as it is sometimes called) have a mortality rate of 90-100% and have been found in at least 25 US states (“Ranavirus,” 2017). According to acvp.org, ranavirus may have first infected fish before shifting hosts and infecting frogs. In fact, the same class of virus infects reptiles as well (“Ranavirus,” n.d.). A 2017 article from Virology describes three types of strains: FV3-like, CMTV-like and ATV-like ranaviruses. Amphibian infections seem to be attributed to the FV3-like strain (Price et. al, 2017). However, there is evidence that the FV3-like strain can infect fish, too. (“Ranavirus,” n.d.).

What’s the difference between chytrid and ranavirus?

The biggest difference between the two is that chytrid is a fungus and ranavirus is, as the name suggests, a virus. Unfortunately, both infectious diseases can occur together simultaneously. One study in Costa Rica found that chytrid incidence and ranavirus incidence were roughly equal at 21.3% and 16.6% respectively (Whitfield, Geerdes, Chacon, Rodriguez, Jimenez, Donnelly, & Kerby 2013).

Just like some species are naturally resistant to chytrid, ranavirus is not universally lethal. It seems to affect amphibians of the order Anura and Caudata (“Ranavirus,” n.d.). So far in the United States, ranavirus has been found in 16 species of frogs, one species of toad, and 6 species of salamander (“Ranavirus,” 2017). Infection can begin within seconds of contact and it can take anywhere from a few days to a few weeks for an amphibian to succumb to the virus (“Ranavirus,” n.d.).

What about Virginia specifically?

Ranavirus is alive and well in Virginia, affecting amphibians and box turtles alike. It’s shown up on both public and private lands; even wildlife refuges aren’t immune (“Ranavirus: Frequently Asked Questions,” 2014).

Good healthy tadpoles in Fredericksburg, VA

What does an infected amphibian look like?

I didn’t want to include pictures that aren’t mine for fear of violating copyright laws, but according to the VA Herpetological Society, symptoms include:

  • Swelling of the legs and body
  • Lethargy
  • Anorexia
  • Hemorrhaging
  • Widespread death of a large number of individuals simultaneously

Ranavirus is most common in the larval form, particularly affecting individuals from the Ambystoma genus, i.e. mole salamanders, and true frogs (“Ranavirus: Frequently Asked Questions,” 2014).

What can citizens do to help?

Unlike chytrid, we have a pretty good idea of where ranavirus came from; it looks like its spread can be attributed to the pet trade and the use of baits (“Ranavirus,” n.d.). Studies show that the use of non-native species in outdoor gardens (Asian newts, American bullfrogs, carp, goldfish, etc) can introduce ranavirus to native populations (Price et. al, 2017). To help prevent introducing or spreading this disease, citizens can:

  • Wash boots, nets and containers after being out in the field
  • Never translocate an individual from one area to another
  • Do not dump aquarium water or substrate from captive animals outside
  • Do not release captive animals outside
  • Do not stock outdoor topiaries or ponds with non-native wildlife ( “Ranavirus: Frequently Asked Questions,” 2014).

Furthermore, use good hygiene when handling animals and try to wash your hands between live captures. Because ranavirus also affects snakes, lizards, turtles and fish, having good practices in the field will help all of our ectothermic brethren!

Lastly, consider logging observations in iNaturalist so that scientists can use that data for conservation efforts in the future!!

Sources:

Whitfield, S., Geerdes, E., Chacon, I., Rodriguez, E. B., Jimenez, R., Donnelly, M., & Kerby, J. (2013). Infection and co-infection by the amphibian chytrid fungus and ranavirus in wild Costa Rican frogs. Diseases of Aquatic Organisms, 104(2), 173-178. doi:10.3354/dao02598

Price, S. J., Ariel, E., Maclaine, A., Rosa, G. M., Gray, M. J., Brunner, J. L., & Garner, T. W. (2017). From fish to frogs and beyond: Impact and host range of emergent ranaviruses. Virology, 511, 272-279. doi:10.1016/j.virol.2017.08.001

Ranavirus. (n.d.). Retrieved April 20, 2019, from https://www.acvp.org/page/Ranavirus

Ranavirus. (2017). Retrieved April 20, 2019, from https://www.northeastwildlife.org/disease/ranavirus

Ranavirus: Frequently Asked Questions. (2014). Retrieved April 20, 2019, from https://virginiaherpetologicalsociety.com/research/disease/_pdfs/NEPARC_Ranavirus_FAQ.pdf

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