Assessing the Impact of Toxoplasma gondii in Endangered Eastern Barred Bandicoots (Perameles gunnii) on Phillip and French Islands, Australia.

Some Australian marsupial species are believed to have a high likelihood of death following infection with the protozoan parasite Toxoplasma gondii. The impacts of T. gondii on free-ranging marsupial populations have not, however, been well demonstrated, with most studies only reporting seroprevalence. This parameter alone does not allow assessment of the impact of infection and may underestimate the incidence of exposure in species highly susceptible to fatal disease. We used multiple diagnostic methods on two free-ranging eastern barred bandicoots (Perameles gunni) populations and one long-nosed potoroo (Potorous tridactylus) population to assess the impacts of T. gondii. Animals had their serological status to T. gondii determined using the modified agglutination test (MAT). Three MAT-positive results were returned from 212 bandicoot blood samples collected from 159 individuals, whereas 16.7% (7/42) potoroos were MAT positive. Animals available for necropsy underwent histopathologic examination and had tissues tested for T. gondii by quantitative PCR (qPCR). Toxoplasmosis was diagnosed by histopathology in 13.1% (18/137) of bandicoots, and more than half of these animals had severe disease. Positive qPCR results were returned in 19.2% (37/193) of bandicoots and 12.5% 7/56) of potoroos. The high prevalence of T. gondii infection demonstrated by qPCR and the observation that >50% of histopathology-positive bandicoots had severe toxoplasmosis demonstrates that infection is an issue of population importance. This result, coupled with the low number of MAT-positive bandicoots detected, suggests that eastern barred bandicoots are highly likely to die within weeks of exposure to T. gondii, before immunoglobulin G antibodies are formed. This contrasts with sympatric potoroos, assumed to be exposed to T. gondii with comparable frequency to bandicoots. The potoroos showed a T. gondii antibody prevalence similar to their qPCR antigen prevalence, suggesting survival after infection.