Status of bovine tuberculosis in Addis Ababa dairy farms

The study was conducted to determine the status of bovine tuberculosis in Addis Ababa, Ethiopia, by a comparative intradermal tuberculin test of 1,869 animals in 106 farms. Epidemiological information was also collected, taking into account factors chosen for their epidemiological significance and local livestock husbandry characteristics. In addition, milk samples were collected from tuberculin reactors for mycobacterial isolation and characterisation. Chi-square statistic, simple regression and multiple stepwise logistic regression were used to analyse the data. Of the 106 farms examined, 46 (95% confidence interval [CI]: 33.8% to 53.4%) contained comparative skin test reactors. Of the 1,869 animals, 443 (95% CI: 21.8% to 25.7%) were comparative skin test reactors. Furthermore, about 8.5% of tuberculin sensitive cows (12 of a sample of 141) secreted acid-fast bacteria in their milk. The microbes are described in more detail in the paper. Factors identified as possibly increasing the risk of bovine tuberculosis in Addis Ababa were herd size (large herd), farming (housing) condition (poor), and age (older animals). Similarly, as body condition scores improved from poor to medium and then to good, the likelihood of positive results significantly decreased (OR = 0.54; p < 0.01). Other factors including breed, sex, and physiological status of animals did not seem to significantly contribute to tuberculin sensitivity. The finding that large-size and intensively (often poorly) managed herds were at greater risk of bovine tuberculosis suggests that the significance of bovine tuberculosis is increasing in Addis Ababa parallel to an increasing dairy operation. If measures are not taken promptly, the impact on the economy and public health could be enormous.