Human TB Due to M. bovis
It is unknown what the contribution of zoonotic TB is to the total number of human TB cases in Malawi since laboratory facilities that allows differentiation between M. bovis and M.
tuberculosis are not readily available. It is alarming though that a prevalence of as high as 42.8% M. bovis-positive specimens have been reported in TB patients in some sections in Malawi (Bedard et al. 1993). These hotspots appear to occur in areas where European cattle breeds had initially been introduced to establish a dairy industry.A more recent epidemiologic study of human TB in Malawi (Nyirenda 2006) revealed a 45% increase in notified cases between 1994 and 2003; about half of these were reported from the urban districts of Blantyre, Zomba, Lilongwe, and Mzuzu. Overcrowding and the HIV epidemic appear to be the main driving forces of this increase. Of the new TB cases reported, 23% (range = 20-27%) during the period were extra-pulmonary, and many of them are likely to be zoonotic M. bovis infections (Kazwala et al. 2001). Owing to the ongoing population growth and urbanization, smallholder dairy farming in Malawi is expected to expand to meet the increasing demand for milk and milk products (Tebug et al. 2012), and unless BTB is adequately controlled, it should be expected that zoonotic TB would remain a major risk factor for the general population.
It is concerning that there is a varying and sometimes very limited awareness by the general population about zoonotic tuberculosis and the persistence of unhygienic practices that increase the risk of contracting zoonotic TB. Although in one survey 74.3% (n = 140) of respondents knew that M. bovis can be transmitted to humans and 67.0% knew that it is transmitted by infected milk, 96.4% of the respondents reported that they still engage in risky farm practices, including the sale (67.0%) and consumption (34.0%) of unpasteurized milk (Tebug et al. 2014). The practice of souring milk into “Chambiko” (instead of boiling or pasteurization) too does not fully eliminate the risk of exposure to milk-borne M. bovis (Hailemariam 2014). It is difficult to explain the mismatch between farmers’ awareness levels about zoonotic TB and their lack of application of preventive measures (Tebug 2013). There thus remains an urgent need to raise the awareness of all stakeholders about the risk and the control measures of zoonotic TB given the extent of their exposure to M. bovis- infected milk.
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