Spontaneous reoccurrence of Batrachochytrium dendrobatidis infections in Australian green tree frogs (Litoria caerulea) following apparently successful heat therapy: Case report

Heat therapy has been reported as a safe, effective, and readily available treatment method for heat-tolerant frogs infected with Batrachochytrium dendrobatidis ( Bd ). We treated wild-caught Australian green tree frogs ( Litoria caerulea ) infected with Bd using two periods of elevated ambient room temperature (28.2–30.3 °C for 7 weeks followed by 28.9–34.1 °C for 4 weeks). Frogs exhibited persistent and even increasing infection loads in the first treatment period despite prolonged exposure to elevated temperatures, likely due to the presence of cooler microenvironments within their enclosure (25.5–27.0 °C). All frogs eventually returned negative qPCR tests for Bd at the end of the second treatment period, but detectable infections reoccurred one month after frogs were returned to standard housing temperatures (21.2–28.7 °C). Our findings suggest that elevated ambient temperature alone might not eliminate Bd in vivo but can reduce infections loads such that they are undetectable by qPCR analysis of skin swabs. Additional factors, such as cooler microenvironments within enclosures or relative humidity, may influence the success of heat therapy. We recommend further research into the combined effects of temperature and humidity during heat therapy and emphasize the importance of accurate temperature measurements as well as post-treatment monitoring at Bd -permissive temperatures to confirm successful clearance of infections.