Temporal and spatial dynamics of trypanosomes infecting the brush-tailed bettong (Bettongia penicillata): a cautionary note of disease-induced population decline

Abstract

BackgroundThe brush-tailed bettong or woylie (Bettongia penicillata) is on the brink of extinction. Its numbers have declined by 90% since 1999, with their current distribution occupying less than 1% of their former Australian range. Woylies are known to be infected with three different trypanosomes (Trypanosoma vegrandis, Trypanosoma copemani and Trypanosoma sp. H25) and two different strains of T. copemani that vary in virulence. However, the role that these haemoparasites have played during the recent decline of their host is unclear and is part of ongoing investigation.MethodsWoylies were sampled from five locations in southern Western Australia, including two neighbouring indigenous populations, two enclosed (fenced) populations and a captive colony. PCR was used to individually identify the three different trypanosomes from blood and tissues of the host, and to investigate the temporal and spatial dynamics of trypanosome infections.ResultsThe spatial pattern of trypanosome infection varied among the five study sites, with a greater proportion of woylies from the Perup indigenous population being infected with T. copemani than from the neighbouring Kingston indigenous population. For an established infection, T. copemani detection was temporally inconsistent. The more virulent strain of T. copemani appeared to regress at a faster rate than the less virulent strain, with the infection possibly transitioning from the acute to chronic phase. Interspecific competition may also exist between T. copemani and T. vegrandis, where an existing T. vegrandis infection may moderate the sequential establishment of the more virulent T. copemani.ConclusionIn this study, we provide a possible temporal connection implicating T. copemani as the disease agent linked with the recent decline of the Kingston indigenous woylie population within the Upper Warren region of Western Australia. The chronic association of trypanosomes with the internal organs of its host may be potentially pathogenic and adversely affect their long term fitness and coordination, making the woylie more susceptible to predation.

First report of Trypanosoma vegrandis in koalas (Phascolarctos cinereus)

“…The PCR prevalence of T. vegrandis in koalas (13.6%) reported in the present study was at the lower end of prevalence estimates of T. vegrandis previously reported in woylies (14% -46%) [5,[15][16] and various other marsupial (up to 32%) [5] and bat species (88.9%)…”

“…Of the eight native trypanosomes formerly described, only T. copemani and T. vegrandis species have been identified in multiple hosts, with the chronic effects of T. copemani infections possibly linked with the decline of woylie populations [5,16]. The current findings add more evidence to the fact that trypanosomes in Australian marsupials comprise a heterogeneous community, with low levels of host specificity and no evidence of restricted geographical distribution [1,4,5,[14][15][16][17].…”

Host stress physiology and Trypanosoma haemoparasite infection influence innate immunity in the woylie ( Bettongia penicillata )

“…found that Clade A, including Trypanosoma copemani, appears more virulent and prevalent in a declining woylie population (Upper Warren, Western Australia) compared to a higher prevalence of less virulent clades in a stable population (Karakamia Wildlife Sanctuary, Western Australia) [15] . This observation has been further supported by a temporal association between decline patterns in the Upper Warren and T. copemani prevalence [16]. It has been suggested that woylies in the declining population may be less efficient at responding to more virulent genotypes of this endemic parasite [15].…”

“…We used an established and validated PCR protocol to detect Trypanosoma parasites in the blood stream of woylies [15,16,36]. DNA extraction and Trypanosoma PCR amplification were carried out as per previously described protocols [15,16,36].…”

“…have been identified as possible disease candidates due to their association with the decline of the woylie [15,16].…”