Mycobacterium bovis Population Structure in Cattle and Local Badgers: Co-Localisation and Variation by Farm Type

Abstract

Bovine tuberculosis surveillance in Northern Ireland includes Multiple-Locus Variable number tandem repeat Analysis (MLVA) to determine the Mycobacterium bovis genetic type present in both cattle and the predominant wildlife host, the European badger (Meles meles). These data are useful for investigating clusters of infection and understanding the scale at which interspecific transmission may occur. We utilised a comprehensive dataset of routinely sampled isolates from infected cattle and from badgers killed in road-traffic accidents to investigate the spatial co-location of MLVA types in, and between, the badger and cattle populations. Furthermore, we investigated the hypothesis that the type of farming enterprise might explain some variation in this relationship. MLVA types were spatially co-localised in cattle and road-traffic accident (RTA) badger hosts, indicative of a shared epidemic. Dairy herds were more likely to have at least one MLVA type in common with nearby RTA badgers, compared to non-dairy herd types. Marginally more MLVA spatial clustering was observed in non-dairy herds, which may be a consequence of relatively more between-herd movements. For the cattle population, local transmission mechanisms such as infection from contiguous herds, infectious wildlife and short-range between-herd cattle movements appear primarily to drive the epidemic: there appears to be a more limited role for long-range movements. Animal management practices are likely to be the driving force behind this observation, as beef rearing is associated with elevated numbers of animal movements compared to dairy herds.

Investigating Farm Fragmentation as a Risk Factor for Bovine Tuberculosis in Cattle Herds: A Matched Case-Control Study from Northern Ireland

“…Previous molecular studies from NI have revealed considerable spatial clustering of M. bovis genetic types in host populations, thereby affirming the important role of geographically localised processes in maintaining the bTB epidemic [ 35 , 36 , 37 , 38 ]. Although NI’s highly fragmented farmland is thought to be a contributing factor hampering eradication efforts, no studies to date have explored farm fragmentation as a risk factor for bTB, necessitating a deeper delve into the role of farm fragmentation as a facilitator of localised disease spread.…”

Quantifying Land Fragmentation Metrics for Cattle Enterprises in Northern Ireland

“…This suggests that on the whole, the majority of individual fragments are in relatively close proximity to each other and the registered farmstead address. We would suggest, therefore, that at broad spatial scales (eg (Milne et al, 2020), the error introduced by imprecise herd locations may be minimal. For studies taking place at much smaller spatial extents, however, the discrepancies introduced from spatial irregularities may be of greater consequence.…”

The impact of Mycobacterium tuberculosis complex in the environment on one health approach

“…Their study suggested that contaminated environment, such as at animal aggregation sites, played pivotal roles in the infection of MTBC in wild rodents and wild boars. In the United Kingdom and Ireland, researchers used GPS collars on cattle and badgers to track their activities and found that the direct contact between cattle and wild animals is actually fairly limited, indicating that direct transmission of tuberculosis may not be the main mechanism of interspecies transmission, implying the elevating possibility of indirect transmission through a contaminated shared environment ( 29 , 30 ). In Michigan US, there is evidence that MTBC in the environment of feed contaminated by wild deer suffering from tuberculosis can also cause tuberculosis in cattle, and this has been further confirmed in the laboratory ( 31 ).…”