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Toxoplasma gondii in Australian Marsupials

Parameswaran, Nivethitha (Nevi) (2008) Toxoplasma gondii in Australian Marsupials. PhD thesis, Murdoch University.

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Diagnostic tools were developed and utilised to detect Toxoplasma gondii infection in a range of Australian marsupial species and identify epidemiological trends. An ELISA was developed to detect anti-T. gondii IgG in macropod marsupials. When compared with the commercially available MAT (modified agglutination test), the ELISA was in high agreement and yielded a ê coefficient of 0.96. Of 18 western grey kangaroos (Macropus fuliginosus) tested for the presence of T. gondii DNA by PCR, the 9 ELISA positive kangaroos tested PCR positive and the 9 ELISA negative kangaroos tested PCR negative indicating that the ELISA protocol was both highly specific and sensitive and correlated 100% with the more labour intensive PCR assay.

A T. gondii seroprevalence study was undertaken on free ranging Australian marsupials. There was a T. gondii seroprevalence of 15.5% (95%CI: 10.7-20.3) in western grey kangaroos located in the Perth metropolitan area. The T. gondii seroprevalence in male western grey kangaroos was significantly less than their female counterparts (p=0.038), which may be related to behavioural differences causing differences in exposure to oocysts or recrudescence of T. gondii infection in pregnant females. Marsupial populations located in islands free from felids had a low overall T. gondii seroprevalence. A case control study determined that marsupials located in areas where felids may roam are 14.20 (95%CI: 1.94-103.66) times more likely to be T. gondii seropositive than marsupials located on felid-free islands.

PCR, immunohistochemistry and serological techniques were used to detect T. gondii infection in marsupial dams and their offspring. T. gondii DNA was detected in the pouch young of chronically infected western grey kangaroos and a woylie (Bettongia penicillata). T. gondii DNA was also identified in the mammary gland of the woylie dam suggesting that infection of the woylie pouch young was from suckling milk from the mammary gland. Results of the study demonstrate that vertical transmission of T. gondii occurs in Australian marsupials and may be of importance in the maintenance of T. gondii infection in Australian marsupial populations.

Animal tissue and meat from Australia, predominately from Australian marsupials, were screened for T. gondii DNA using PCR primers for the multi-copy, T. gondii specific B1 gene. Sequencing of the B1 gene revealed atypical genotypes in 7 out of 13 samples from Australia. These 7 isolates contained single nucleotide polymorphisms (SNPs) in the B1 gene that could not be matched with known sequences from strains I, II, III and X. Six unique genotypes were identified out of the 7 atypical isolates; two out of the 7 isolates had the same unique sequence at the B1 gene whereas the other 5 isolates each had different combinations of SNPs at the B1 gene. A majority of T. gondii isolates sampled from native Australian marsupials were of an atypical genotype. The discovery of atypical strains of T. gondii in Australia leads to further questions regarding the origin and transmission of these atypical strains. Additional studies linking atypical strains with their clinical manifestation are also warranted.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Biomedical Sciences
Supervisor(s): Thompson, Andrew, O'Handley, Ryan and Fenwick, Stan
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