Molecular epidemiology of Mycobacterium bovis in central parts of Malawi

Bovine tuberculosis (bTB) is a neglected disease that affects cattle and humans. The burden of bTB is higher in developing countries as compared to industrialized countries. The reasons behind this discrepancy include the fact that bTB control measures, such as testing and slaughter of infected cattle and pasteurization of milk, are not usually practised in developing countries largely because of their high cost. To improve our understanding of bTB in developing countries, molecular typing studies are essential, in particular in terms of transmission dynamics, infection sources and knowledge of circulating strains of the principal causative agent, Mycobacterium bovis. In this study, we applied a suite of molecular typing techniques encompassing deletion analysis, spoligotyping and MIRU-VNTR to isolates recovered from samples collected during the routine post-mortem of cattle at the cold storage abattoir in Lilongwe, Malawi. Out of 63 isolates, 51 (81%) belonged to the European 1. M. bovis clonal complex. Spoligotyping identified 8 profiles, with SB0131 being the predominant type (56% of isolates). Spoligotypes SB0273 and SB0425 were identified in 14% and 13%, respectively, of the isolates. MIRU-VNTR showed a high discriminatory power of 0.959 and differentiated the 8 spoligotypes to 31 genotypes. The high diversity of M. bovis within the study area suggests the infection has been circulating in the area for a considerable period of time, likely facilitated by the lack of effective control measures. We also observed genetic similarities between isolates from Malawi (this study) to isolates described in previous studies in Zambia and Mozambique, suggesting transmission links in this region. The information provided by this study provides much needed evidence for the formulation of improved bTB control strategies.