Investigating the spatial distribution of Bovine Tuberculosis(BTB) herds of Cattle in Namwala District of Zambia

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Tembo, Novan F.P.
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The overlap in grazing pastures and water points at the wildlife-livestock interface area among different wildlife species and livestock have been recognised as “hot” spots for disease transmission. It is a major driver for bovine tuberculosis (bTB) occurrence in the Kafue flats. To investigate this phenomenon, Geographical Positioning System (GPS) coordinates representing 96 herds across 20 villages were captured alongside biological and risk factor data. The GPS coordinates were transferred into Arc-View 3.2 and laid onto the map of Namwala district. To understand relationships with the environment, map overlays were done to incorporate physical features including National Parks, Game Management Areas (GMA) and flood plains. In addition, Questionnaires were administered across 96 independent households to assess risk factors of bTB transmission to livestock. The results revealed a spatial distribution of the disease in cattle in Namwala district of Zambia, with an ecological interplay in the high bTB prevelance areas which were a function of existing reserviour hosts. That was particularly significant in the eastern interface areas of the District where autocorrelation between high prevalence in cattle and the environment was found to be significant using Moran’s I statistic (p-value=0.006). This indicated the marked tendency for aggregation of the positive bTB cases which may be due to the overlapping effect of cattle and wildlife in grazing areas. Further, on epidemiological studies, a total of 35 herds were found positive representing a prevalence of 36.4% (95% CI=26.7-46.3%). Individual herd prevalence across the study area ranged from 0% to 14% (95%=2.4-26.2%). The possible risk factors contributing to the spread of the disease to livestock were contact with wildlife during grazing and at water points. We also looked at the potential for bTB to be transmitted to humans. Risk factors underlying such possible transmission included low BCG vaccination at only 30%, only 40% having knowledge of bTB and only 26% reporting boiling of milk while frequency of drinking milk at least three times a week was as high as 82%. On logistic regression, cattle sharing watering points with wild animals were 5.5 more likely to belong to bTB positive herds. The use of GIS in this epidemiological study has shown that bTB is skewed to the Eastern side of Namwala in distribution. Mitigation measures against this disease should therefore prioritise this region of the district.
Tuberculosis, Bovine , Zoonoses-Microbiology , Microbacterium Bovis Pathogenicity