Distribution, prevalence and persistence of mucormycosis in Tasmanian platypuses (Ornithorhynchus anatinus)

Abstract

While the fungal disease mucormycosis has infected Tasmanian platypuses for nearly three decades, its impacts remain largely unknown. This study documents the spatial and temporal distribution of mucormycosis in Tasmanian platypuses as a baseline for assessing its impacts. Over 1800 platypus capture and observation records were collated and mapped, and indicate that between 1982 and 2007 mucormycosis-infected platypuses were present in at least 11, and potentially 22, of Tasmania’s 48 river catchments. During 2008–09, live-trapping surveys were undertaken to determine the spread, prevalence and persistence of the disease. Surveys of 75 rivers and creeks across 18 catchments captured 167 individuals, and an additional 12 platypuses were obtained from the public. Only seven of the 179 sampled animals were ulcerated with clinical signs of mucormycosis. All infected individuals were obtained from catchments with prior histories of disease, where platypuses have persisted despite mucormycosis being present for up to 20 years. Detection probabilities were calculated to estimate the probability that the other surveyed catchments are currently disease free. Detection probabilities were generally high (>0.75) per catchment, indicating that sampling effort was adequate to reliably detect diseased animals at historically reported prevalence (which averaged 0.295 from surveys undertaken between 1994 and 2000). Mean disease prevalence in affected catchments sampled during the present study declined to 0.071. This significant four-fold reduction in prevalence makes disease detection more challenging and increased sample sizes are required to confidently assert that some catchments are currently disease free. Reduced disease prevalence suggests that mucormycosis is exerting less impact on Tasmanian platypuses now than it was in the mid to late 1990s; however, the individual consequences of infection are poorly understood and require further investigation.