Molecular epidemiology of Mycobacterium bovis in central parts of Malawi

Abstract

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.

Prevalence and risk factors of bovine tuberculosis in slaughtered cattle, Malawi

“…In Malawi, livestock are crucial to people's livelihoods, as they are in many other developing countries, such that the interaction between people and their livestock is unavoidable [ 3 ]. The spread of bTB to and within Malawi could be exacerbated by multiple factors such as; open local borders (allowing unregulated animal movement) between Malawi and neighbouring countries where bTB is documented as ‘enzootic’ [ [4] , [5] , [6] ], traditional livestock production systems characterised by communal grazing and mixing of animals from various localities.…”

“…In our recent molecular epidemiological study, we revealed a high genetic diversity of M. bovis strains circulating in central Malawi [ 3 ] However, the general epidemiology and risk factors associated with bTB in cattle in Malawi are still required for a better understanding of the disease. Therefore, this study aimed to generate updated bTB epidemiological evidence in cattle and highlight the zoonotic TB threat to humans in Malawi.…”

“…In all the three abattoirs, ante- and post-mortem procedures were similar. Routine meat inspection was carried out as described in our earlier publication [ 3 ]. Slaughtered cattle were examined and only one lesioned tissue sample with granulomatous bTB-like lesions was collected per animal and transportation to the National Tuberculosis Reference Laboratory (NTRL) in Lilongwe for storage at −20 °C until processed.…”

“…Collected samples were processed and cultured in the BACTEC Mycobacterial growth indicator tube (MGIT) as described previously [ 3 ]. Briefly, all the fat and connective tissue were removed from the sample using a pair of sterile scissors and forceps.…”

“…Out of 112 DNA samples, 87 (77.67%) were detected as MTBC ( Table 2 ). Then, we performed a multiplex PCR [ 16 ] as described previously [ 3 ] for differential detection of M. bovis and M. tuberculosis . The confirmation was based on the amplicon sizes i.e., 168 bp for M. bovis and 337 bp for M. tuberculosis .…”