This week a new HALI publication was released on Preventive Veterinary Medicine. The article led by Dr. Annette Roug tackles the challenging issue of reducing exposure of pastoralists in the Ruaha Landscape of Tanzania to Mycobacterium bovis, a pathogen that can be transmitted from livestock to people through milk and that can cause tuberculosis. In most areas of the world, testing for M. bovis is done in dairy herds and at the expense of the dairy owner. In the community where HALI works, costs for testing and disease control are simply too much for pastoral producers. So, Dr. Roug and her team evaluated different methods that could reduce exposure of people to infected milk using a Reed-Frost model, a mathematical model for epidemics that looks at how an epidemic behaves over time.
The model, using a 10-year simulation period, showed that "boiling milk 80% of the time is necessary to obtain a reduction in liters of infectious milk approximately equivalent to what would be obtained with a standard 2-year testing and removal regimen, and that boiling milk was more effective than animal test and removal early in the time period."
The model results also showed that even M. bovis testing and removing infected cattle, "a residual risk of exposure to infectious milk remained due to imperfect sensitivity of the skin test and a continuous risk of introduction of infectious animals from other herds." No test is perfect, and in the Ruaha landscape where herds often mix in grazing areas or grow and shrink in trades and gifts, there is no perfect way to control for M. bovis using the same methods promoted in commercial operations.
According to Dr. Roug, until bTB control programs can be implemented in these areas, the best strategy for protecting people from exposure to M. bovis is through treating milk, by boiling it to kill the bacteria.