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The epidemiology of brucellosis in Timor, Indonesia

Geong, Maria (1999) The epidemiology of brucellosis in Timor, Indonesia. PhD thesis, Murdoch University.

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Bovine brucellosis is a serious disease of cattle in many countries of the world. The study outlined in this thesis was conducted to investigate the distribution and epidemiology of bovine brucellosis in Timor, Indonesia. The current study found that brucellosis was prevalent in Timor with 19.2% of 3890 cattle tested being seropositive. However the prevalence varied significantly between districts (range 3 to 58.8%) and villages (0 to 76.6%). The practice of moving cattle, without testing, between districts is likely to have allowed the rapid distribution of infection throughout Timor. Furthermore management practices including running animals in large groups and keeping old cows all were shown to significantly increase the risk of infection. The high seroprevalence in some villages was found to be having a significant effect on the productivity of animals from these villages. Seropositive animals were 13.8 times more likely to have an abortion and 9.7 times more likely to have had a stillbirth delivery than seronegative cows. In contrast seronegative animals were 4.2 times more likely to have produced healthy calves than seropositive cows.

Only Brucella abortus biotype 1 was cultured from cattle in Timor. The bacterium was cultured more successfully from hygromas (47.9%) than from lymph-nodes (18.5%). Of the lymph nodes B. abortus was cultured more frequently from the supramammary than from any other nodes. Digests of DNA resolved by pulsed field gel electrophoresis found that all isolates (both from Timor, strain 19 and type isolates) had the same pattern. From this result it is likely that B. abortus is clonal however further extracts need digesting with other restriction enzymes to confirm this observation.

The results of a 24 month vaccination trial with strain 19 confirmed that this vaccine induces a significant serological response, both in calves and cows, in Bali cattle. In contrast to vaccinated animals more in-contact non-vaccinated control animals developed serological evidence of brucellosis. However some (< 2%) vaccinated animals still were seropositive 24 months after vaccination and care will be required when interpreting the serological response of a small proportion of vaccinated cows. An economic evaluation of the benefit of vaccinating adult cows with low dose strain 19 showed that vaccination was highly profitable with returns of over 2000%. This in part was due to the high prevalence in Timor, the low costs of farming livestock and the significant losses induced by brucellosis.

Serological evidence of infection was also found in buffalo (8.3%) and pigs (5.1%). However it is likely that these animals play only a minor role in the spread of bovine brucellosis. Twelve percent of humans tested were seropositive to brucellosis. Occupation was identified as a significant risk factor for infection in humans. It is concluded that vaccination of adult cows with low dose strain 19 will, not only have a significant impact on the losses from brucellosis and hence improve the productivity and profitability of cattle in Timor, but also will reduce the prevalence of disease in humans and other species.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): Division of Veterinary and Biomedical Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Robertson, Ian
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