Structured surveys of Australian native possum excreta predict Buruli ulcer occurrence in humans

Abstract

Buruli ulcer (BU) is a neglected tropical disease caused by infection of subcutaneous tissue with Mycobacterium ulcerans. BU is commonly reported across rural regions of Central and West Africa but has been increasing dramatically in temperate southeast Australia around the major metropolitan city of Melbourne. Previous research has shown that Australian native possums are reservoirs of M. ulcerans and that they shed the bacteria in their fecal material (excreta). Field surveys show that locales where possums harbor M. ulcerans overlap with human cases of BU, raising the possibility of using possum excreta surveys to predict the risk of disease occurrence in humans. We thus established a highly structured 12-month possum excreta surveillance program across an area of 350 km2 in the Mornington Peninsula area 70 km south of Melbourne, Australia. The primary objective of our study was to assess if M. ulcerans surveillance of possum excreta provided useful information for predicting future human BU case locations. Over two sampling campaigns in summer and winter, we collected 2282 possum excreta specimens of which 11% were PCR positive for M. ulcerans-specific DNA. Using the spatial scanning statistical tool SatScan, we observed non-random, co-correlated clustering of both M. ulcerans positive possum excreta and human BU cases. We next trained a statistical model with the Mornington Peninsula excreta survey data to predict the future likelihood of human BU cases occurring in the region. By observing where human BU cases subsequently occurred, we show that the excreta model performance was superior to a null model trained using the previous year's human BU case incidence data (AUC 0.66 vs 0.55). We then used data unseen by the excreta-informed model from a new survey of 661 possum excreta specimens in Geelong, a geographically separate BU endemic area to the southwest of Melbourne, to prospectively predict the location of human BU cases in that region. As for the Mornington Peninsula, the excreta-based BU prediction model outperformed the null model (AUC 0.75 vs 0.50) and pinpointed specific locations in Geelong where interventions could be deployed to interrupt disease spread. This study highlights the One Health nature of BU by confirming a quantitative relationship between possum excreta shedding of M. ulcerans and humans developing BU. The excreta survey-informed modeling we have described will be a powerful tool for efficient targeting of public health responses to stop BU.

Mycobacterium ulceransnot detected by PCR on human skin in Buruli ulcer endemic areas of south eastern Australia

“…A second was from the elbow of a female from an endemic area (38.33, 38.49). The third was an ankle swab from one of the researchers (KV) who worked outdoors while collecting possum excreta, a significant proportion of which was later shown to be heavily contaminated with M. ulcerans [24]. Ct values from KV’s ankle swab in January 2019 were 37.11, 37.16 and 37.49.…”

A transmission chain linkingMycobacterium ulceranswithAedes notoscriptusmosquitoes, possums and human Buruli ulcer cases in southeastern Australia

“…These secondary clusters can be indicative of sub-clusters within the primary cluster or potentially distinct clusters that are spatially adjacent to the primary cluster. The Mornington Peninsula surveillance data used in these analyses consisted of trapped mosquitoes (177 traps screened for IS2404 collected: 12/11/19 to 20/03/20), M. ulcerans detected in possum excreta collected during the summer (December to February) of 2019 using data from a previous study 47 and notified human Buruli ulcer cases from the study area in the years 2019-2020. The use of possum excreta collected during the summer was appropriate as Buruli ulcer transmission is most likely to occur during that time of year 48,49 .…”

“…geographic information system software 45 . The latitude and longitude (projected in GDA94) were derived from the centroids of the mesh block polygon OFFICIAL OFFICIAL ulcerans detected in possum excreta collected during the summer (December to February) of 2019 using data from a previous study 47 and notified human Buruli ulcer cases from the study area in the years 2019-2020.…”

“…notoscriptus (Figure 3B). We also included sequence capture enrichment results for two IS2404 positive possum excreta specimens, collected as part of a large field survey of M. ulcerans in Australian native possums in the region 43 . More than 500,000 reads were obtained from these samples (primary IS2404 Ct values <23).…”

Possum faeces, the "canary in the coalmine" heralding the emergence of Buruli ulcer in an Australian urban centre.

“…Unlike in Africa, Australia shows evidence of zoonotic transmission, notably from native ringtail (Pseudocheirus peregrinus) and brushtail (Trichosurus vulpecula) possums [14,15]. Possum faeces at a residential property positive for M. ulcerans DNA correlated with higher likelihood of BU among residents [16,17]. Surveillance in possums enhances human case prediction [17], yet the timing of infection in possums related to the emergence of human cases has not been described.…”