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Development of tools to improve the detection of Trypanosoma evansi in Australia

Smuts, Celia (2009) Development of tools to improve the detection of Trypanosoma evansi in Australia. PhD thesis, Murdoch University.

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The aim of this study was to evaluate new methods to improve detection and investigation of the effects of chronic or subclinical infection with Trypanosoma evansi in various mammalian species. Some of the more resistant host species, including pigs and buffaloes, are present in large feral populations in the northern parts of Australia, the area where T. evansi is most likely to gain entry to the country. Existing tests are not sufficiently reliable to detect all cases of disease and they cannot distinguish acute from chronic infections. Furthermore, the tests have different sensitivities in different host species.

Surveillance for trypanosomiasis in Australia is problematic because of the need to work in remote parts of northern Australia where provision of a cold-chain for traditional blood and serum storage is difficult. An existing dried blood storage system was modified by treating cotton lint filter paper (Whatman #903) with a commercial post coating buffer (TropBio, Queensland). This treatment increased the longevity of antibodies to T. evansi in serum and blood stored on the paper (detected using an antibody-detection ELISA) compared to samples stored on plain paper, especially when the papers were stored under humid conditions and at high ambient temperatures.

Attempts were made to improve the diagnostic utility and repeatability of antibody-ELISAs through the use of 2 recombinant T. brucei antigens (PFRA and GM6) and to optimize a competitive ELISA using RoTat 1.2 variable surface antigen and its monoclonal antibody. Antibody-detection using the two recombinant proteins was not sufficiently specific to enable their use for the detection of T. evansi. The RoTat 1.2 cELISA had good sensitivity and specificity (75% and 98% respectively) when used to test serum from cattle and buffaloes experimentally infected with T. evansi and uninfected animals. However, the test was not able to detect anti-T. evansi antibodies in serum from wallabies, pigs, a dog or a horse that were experimentally infected with T. evansi. The inability of the cELISA to detect anti-T. evansi antibodies may be due to the small number of samples tested or the lack of RoTat 1.2 specific antibodies in the animals tested.

The feasibility of using an enzymatic test to detect trypanosome aminotransferase or antibodies to this enzyme was evaluated. Prior publications suggested that the detection of TAT was an appropriate diagnostic tool for the detection of T. evansi infection in camels. However, the results from this study did not support the use of this test for the detection of T. evansi infection in cattle or buffaloes with low to moderate parasitaemia.

Trypanosomiasis is an immunological disease that affects most of the body’s organs, with more severe disease developing over time. Attempts were made to determine key cytokine and biochemical patterns that would distinguish infected from uninfected animals and acute from chronic infections. The results from this study showed that there was no specific pattern in serum cytokines or serum biochemistry that could be used to distinguish infected from uninfected animals, or different stages of disease.

Immunohistochemistry was used on tissues from buffaloes and mice experimentally infected with T. evansi and T. brucei gambiense respectively to characterise the cellular immune response that was present. The immune response was predominantly cell mediated, with CD3+ T lymphocyte and macrophage infiltration occurring in most tissues. In end stage disease there was often suppression of the immune system with disruption of the architecture of the spleen and a decrease in B lymphocytes in the circulation.

Trypanosomes were rarely visible in the tissues and were only seen in those animals with high parasitaemia. Lesions generally became more severe over time, but there was a large variation between animals, which suggests that immunohistochemistry is unsuitable as a diagnostic tool.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary and Biomedical Sciences
Supervisor(s): Reid, Simon
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