Action: Use temperature treatment to reduce chytridiomycosis infection
- Four of five studies (including four replicated, controlled studies) in Australia, Switzerland and the USA found that increasing enclosure or water temperature to 30–37°C for over 16 hours cured frogs and toads of chytridiomycosis. One found that heat treatment at 30–35°C for 36 hours did not cure northern leopard frogs.
Treatment of chytridiomycosis is vital to ensure the success of amphibian captive-breeding programmes. Also to reduce the risk of spreading the disease when animals are moved between captive or wild populations.
The chytrid fungus Batrachochytrium dendrobatidis is very sensitive to temperatures above 32°C. At 37°C the fungus is killed within four hours and at 47°C within 30 minutes (Young et al. 2007). A study found that the probability of infection by chytrid in the wild decreased strongly with increasing time spent with body temperatures above 25°C in three frog species (Rowley & Alford 2013). A study in captivity also found that fewer frogs became infected and died when exposed to the chytrid fungus if they were housed at 27°C rather than 17°C or 23°C (50 vs 100% mortality; Berger et al. 2004). Increasing temperatures within amphibian housing may therefore provide a treatment for chytridiomycosis.
Berger L., Speare R., Hines H.B., Marantelli G., Hyatt A.D., McDonald K.R., Skerratt L.F., Olsen V., Clarke J.M., Gillespie G., Mahony M., Sheppard N., Williams C. & Tyler M.J. (2004) Effect of season and temperature on mortality in amphibians due to chytridiomycosis. Australian Veterinary Journal, 82, 434–438.
Rowley J.J.L. & Alford R.A. (2013) Hot bodies protect amphibians against chytrid infection in nature. Scientific Reports, 3, 1515.
Young S., Berger L. & Speare R. (2007) Amphibian chytridiomycosis: strategies for captive management and conservation. International Zoo Yearbook, 41, 85–95
Supporting evidence from individual studies
A replicated, controlled study in a laboratory at James Cook University, Australia (Woodhams, Alford & Marantelli 2003) found that heat treatment at 37°C cured red-eyed tree frogs Litoria chloris of chytridiomycosis. There was a significant difference in survival between temperature treatments. All infected frogs in the treatment with two eight-hour periods at 37°C tested negative for chytrid after 94 days and survived for at least another five months. Infected frogs at a constant 20°C survived for the shortest period (55 days), while survival was intermediate in the treatments with naturally fluctuating temperatures (14–23°C; 83 days) and two eight-hour periods at 8°C (one frog survived over 94 days). All frogs in these treatments were heavily infected. All but one uninfected frog survived. Eighty juvenile frogs were divided equally into the four temperature regimes. Half in each treatment were infected with chytrid fungus and half with sterile medium as a control. Survival was examined over 94 days and infection level determined at post-mortem.
A replicated, controlled study in 2004 in a laboratory in the USA (Retallick & Miera 2007) found that heat treatment at 32°C cured western chorus frogs Pseudacris triseriata of chytridiomycosis. Three infected frogs died during treatment, but the remaining four tested negative for chytrid following treatment. All infected frogs kept at room temperature remained infected and four died. No uninfected frogs died with or without treatment. Weight gain in cured frogs was significantly greater than infected frogs (1.1–1.4 vs 0.7–0.9 g). Frogs were raised from eggs collected from the wild and were experimentally infected with chytrid. Seven infected and five uninfected frogs were placed in an incubator for five days at 32°C. Nine infected and 15 uninfected frogs were kept at room temperature (20°C). Frogs were weighed at days 172 and 257 and sampled for chytrid on day 172.
A replicated study in 2010 of captive amphibians in Louisiana, USA (Chatfield & Richards-Zawacki 2011) found that temperature treatment at 30°C cured northern cricket frogs Acris crepitans and bullfrogs Rana catesbeiana of chytridiomycosis. All bullfrogs and all but one northern cricket frog (96%) tested negative for chytrid following treatment. Animals were randomly assigned to acclimatization at 23 or 26°C for one month. Sixteen northern cricket frogs (seven at 23°C, nine at 26°C) and 12 bullfrogs (10 at 23°C, two at 26°C) naturally infected with the chytrid fungus were then housed individually at 30°C for 10 consecutive days. Frogs were returned to 23 or 26°C and tested again for infection six days later.
A replicated, controlled study in a laboratory at the University of Zürich, Switzerland (Geiger et al. 2011) found that heat treatment over 26°C cured the majority of common midwife toad Alytes obstetricans tadpoles of chytridiomycosis. The percentage of tadpoles cured increased significantly with temperature (21°C: 20%; 26°C: 63%; 30°C: 88%). Tadpoles were wild caught and were tested for chytridiomycosis before and 6–10 days after treatments. Ten infected tadpoles were randomly assigned to each treatment: water temperature at 21°C or 26°C for five days, or water at room temperature and 30°C for 59 hours. After the experiment, toads were treated using itraconazole fungicide and released at the capture site.
A small, replicated, controlled study in 2007 of captive amphibians (Woodhams et al. 2012) found that short-term heat treatment at 30–35°C did not cure northern leopard frogs Lithobates pipiens of chytridiomicosis. None of the four infected frogs treated were cured of their infection. Five of six uninfected frogs remained uninfected during treatment, but all control frogs kept in group enclosures were infected by the end of the experiment. Naturally infected frogs were placed in an incubator at 30°C overnight and then 35°C for 24 hours. Control groups of 3–4 frogs were kept at room temperature (23°C).
- Woodhams D.C., Alford R.A. & Marantelli G. (2003) Emerging disease of amphibians cured by elevated body temperature. Diseases of Aquatic Organisms, 55, 65-67
- Retallick R.W.R. & Miera V. (2007) Strain differences in the amphibian chytrid Batrachochytrium dendrobatidis and non-permanent, sub-leathal effects of infection. Diseases of Aquatic Organisms, 75, 201-207
- Chatfield M.W.H. & Richards-Zawacki C.L. (2011) Elevated temperature as a treatment for Batrachochytrium dendrobatidis infection in captive frogs. Diseases of Aquatic Organisms, 94, 235-238
- Geiger C.C., Küpfer E., Schär S., Wolf S. & Schmidt B.R. (2011) Elevated temperature clears chytrid fungus infections from tadpoles of the midwife toad, Alytes obstetricans. Amphibia-Reptilia, 32, 276-280
- Woodhams D.C., Geiger C.C., Reinert L.K., Rollins-Smith L.A., Lam B., Harris R.N., Briggs C.J., Vredenburg V.T. & Voyles J. (2012) Treatment of amphibians infected with chytrid fungus: learning from failed treatments with itraconazole, antimicrobial peptides, bacteria, and heat therapy. Diseases of Aquatic Organisms, 98, 11-25