Detection of ranavirus in endemic and threatened amphibian populations of the Australian Wet Tropics Region

Abstract

The amphibian chytrid fungus (Batrachochytrium dendrobatidis) has driven severe amphibian declines in the Australian tropics. These declines have resulted in species extirpations and extinctions, with many surviving in small, highly threatened populations. Despite the fragility of remaining populations, another group of lethal pathogens, ranaviruses, have rarely been investigated among native amphibians. Ranaviruses have previously been associated with fish, reptile and amphibian mortality events in Australia, yet remain poorly understood here, especially among amphibian hosts. Here, quantitative polymerase chain reaction assays were used to detect ranavirus presence from eight of 17 tested sites containing populations of endangered and critically endangered Australian frog species. Although present in these populations, ranavirus seems to be at the lower bounds of detectability of the assay, which makes firm diagnosis at the individual level unreliable. Repeated (n=14) detections of this pathogen, however, are highly indicative of its presence at each area where it was detected. Therefore, these populations are likely often exposed to ranavirus. The results of this study are not characteristic of populations experiencing rapid disease-associated die-offs or declines, but further investigations should be undertaken to examine the potential drivers of these pathogens to predict future emergence and potential threats to endangered Australian amphibians.