Risk analysis of an anthrax outbreak in cattle and humans of Sesheke district of Western Zambia

An anthrax outbreak occurred in November 2010 in five villages of Sesheke district in Western Zambia. Control measures and data collection was carried out immediately the outbreak was reported. The prevalence of the disease in cattle was estimated at 7.4% (45/609) while the average herd size of infected cattle in affected villages was estimated at 121.8 (95% CI 48.8–194.8). Individual mortality per herd varied between 1.70% (3/179) and 20.25% (6/79). The relative risk of infection of cattle in the five affected villages varied between 0.18 (95% CI 0.4–5.7) and 3.7 (95% CI 1.99–6.68). In humans, the disease only affected three people and was characterized by cutaneous carbuncles. The ratio of infected persons per number of infected carcasses varied between 1:37 and 1:49 in affected villages while the overall ratio of people at risk to the number of carcasses was 42:1 indicating that despite availability of a large number of carcasses, human contact with infected carcasses was low. The findings of this study underline the importance of timely disease control measures in reducing the risk of human infections to anthrax in the face of an outbreak.