Investigations into the treatment of Batrachochytrium in frogs and tadpoles

Gerry Marantelli¹, Lee Berger^2,3 and Kelly McInnes⁴

1 Amphibian Research Centre, P.O. Box 424, Brunswick, Victoria, Australia 3056.
2 Division of Animal Health, CSIRO, Ryrie St.,Geelong, Victoria, Australia 3022.
3 School of Public Health and Tropical Medicine, James Cook University, Townsville, Queensland, Australia 4811.
4 School of Ecology and Environment, Deakin University, Clayton, Victoria, Australia 3168.

Effective treatments for Batrachochytrium infection in frogs and tadpoles will be useful in treating outbreaks in captivity and in preventing spread of the fungus when translocating animals between wild and/or captive populations. Tadpoles seem not to be affected by Batrachochytrium although they can be healthy carriers. This offers a good explanation for the persistence of tadpoles in areas where adult frogs have disappeared, and the failure to rear these surviving tadpoles past metamorphosis. Once an outbreak is detected it is often too late to salvage adult frogs, but tadpoles may be removed, treated and held in captivity to provide stock for re-establishing wild populations.

The efficacy of a number of fungicides were tested on the fungus in vitro and treatment regimes safe for the tadpoles of Mixophyes fasciolatus were determined. Itraconazole (Sporanox) was found to be highly toxic to tadpoles at low concentrations. Benzalkonium chloride at 1mg/L (3 hrs for 6 days), fluconazole at 6.6mg/L(6 hrs for 7 days), and methylene blue at 3 then 6mg/L(72 hrs / 72 hrs), were selected for use in a treatment trial. Benzalkonium chloride and fluconazole moderately reduced the prevallence of infection when compared to untreated controls, but methylene blue had no significant effect. As benzalkonium chloride was found to be toxic to tadpoles at higher levels, later attempts will focus on fluconazole at a higher dose. Benzalkonium chloride 1 mg/L and fluconazole at 25 mg/L were also trialled on frogs. Green tree frog metamorphs were exposed to cultured fungus and treatments were started as soon as infection was detected. All frogs eventually died. Itraconazole given orally (Taylor et al, 1999 J Wildl Dis, 35: 49-57) or by bath (Don Nichols, unpub) has been used successfully on adults.