Low humidity is a failed treatment option for chytridiomycosis in the critically endangered southern corroboree frog

Abstract

Context One of the major drivers of the current worldwide amphibian decline and extinction crisis is the spread of the amphibian chytrid fungus, Batrachochytrium dendrobatidis (Bd). Captive assurance colonies may be the only lifeline for some species. Current antifungal chemotherapies can be effective for clearing infection but may have detrimental side effects. The only non-chemotherapeutic treatment that has been clinically tested is heat, which is impractical for cold-adapted species. The fungus does not survive desiccation, and therefore a plausible alternative non-chemotherapeutic treatment would be a low-humidity regimen. Aims We tested the efficacy of a low-humidity treatment regimen for treating Bd-infected animals of the critically endangered species Pseudophryne corroboree. This species has high tolerance of dry environments, and is thus an ideal candidate for this treatment trial. Methods Forty frogs were exposed to 1 × 106 zoospores. At three weeks after exposure access to water was reduced to once daily for 10 days for 20 animals. Ten of these animals were also rinsed daily with the aim of removing zoospores. Key results The drying regimen neither increased survival nor decreased infection load, and treatment may have hastened mortality. All infected frogs died between 21 and 80 days after exposure, except one untreated frog. Conclusions Our results suggest that a drying regimen is not a viable treatment for chytridiomycosis. Infection may decrease the host’s ability to cope with water stress. Implications The failed drying treatment in P. corroboree suggests that drying is not an appropriate treatment for chytridiomycosis and treatment efforts should be focussed on chemotherapies for cold-adapted species. P. corroboree is a critically endangered species for which chytridiomycosis is the primary cause of decline, yet few experiments have been carried out on this species with regards to chytridiomycosis. All experimental information about this species and disease will benefit the management and protection of the species.

Treatment trial of clinically ill corroboree frogs with chytridiomycosis with two triazole antifungals and electrolyte therapy

“…Electrolyte baths would be less stressful and have been suggested as an alternative to injections to reduce stress in sick animals (Pessier and Mendelson 2010;Young et al 2012;Baitchman and Pessier 2013). However, in animals clinically ill with chytridiomycosis, absorption through the skin may be compromised (Carver et al 2010;Brannelly et al 2015) and therefore delivery is uncertain and needs testing. Oral electrolyte dosing appears effective (Voyles et al 2009) but is also stressful.…”

“…Thirdly, the righting reflex was assessed by positioning the frog on its back. If the animal failed all three alertness steps it was considered moribund and treatment commenced (Brannelly et al 2015).…”

“…The species is highly susceptible to chytridiomycosis (Hunter et al 2009;Brannelly et al 2015) and is now functionally extinct in the wild, with only a handful of individuals remaining. The species is currently being sustained by captive assurance colonies in New South Wales and Victoria, Australia, with the hope of reintroduction (Hunter et al 2010;Brannelly et al 2015). The ability to maintain chytridiomycosis-free colonies and halt outbreaks is a high priority .…”

Interactions between amphibian skin sloughing and a cutaneous fungal disease: infection progression, immune defence, and phylogenetic patterns

“…While some amphibian species are considered generally very susceptible to mortality from chytridiomycosis, such as Atelopus zeteki (and likely many other species of this genus) in Central and South America (La Marca et al 2005;Bustamonte et al 2010;Becker et al 2015;Ellison et al 2015), Rana muscosa and Rana sierrae in North America Rosenblum et al 2012), and Corroboree frog species (Pseudophryne corroboree and P. pengilleyi) in Australia Brannelly et al 2015), others appear to be resistant to infection, given they can reduce or eliminate Bd infection loads. There is little definitive evidence of species demonstrating widespread resistance to chytridiomycosis, but some species appear to demonstrate greater resistance than most, including the notorious invader Lithobates catesbeianus (Gervasi et al 2013;Eskew et al 2015), and threatened species in the genus Leiopelma (Bishop et al 2009;), amongst others (Woodhams et al 2007a;Gahl et al 2012;Searle et al 2011b).…”

“…T/E T 11 3 100 (2) Nichols et al 2001;Daszak et al 2004;Courtois et al 2012 Epipedobates tricolor Berger et al 2005c;Voyles et al 2007; Litoria infrafrenata E/P A 127 3 0 (1) Berger et al 2004;Young et al 2014 Litoria verreauxii alpina P T 48 1 97 (1) Osborne et al 1999;Hunter et al 2009;Bataille et al 2015Brannelly et al 2015Scheele et al 2015 Platyplectrum ornatum Rhinella marina Sanchez et al 2008;Shine 2010 90 CHAPTER 5…”