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.
Highlights
The wildlife-livestock interface presents a conduit through which pathogens can be exchanged [1].In the UK and Ireland, the presence of wildlife reservoirs is implicated in the persistence of Mycobacterium bovis, the principal causative agent of bovine tuberculosis in cattle [2,3]
Med: 1; Med: 4.9 km IQR: 3.3–6 km Spatial clustering in M. bovis molecular types, at various genetic and geographic scales, has previously identified co-localisation of infection between infected livestock and wildlife hosts [20,27,28,29,30,31]; little attention has been given to what the patterns in spatial distribution of M. bovis genetic types in NI reveal about the processes driving the epidemic in, and between, hosts
It is already understood that the M. bovis population in Northern Irish cattle herds is characterized by marked spatial structuring and spatial clusters of MVLA types at the herd level [18,19]
Summary
The wildlife-livestock interface presents a conduit through which pathogens can be exchanged [1]. Different herd types have specific between-herd contact patterns potentially linked to different infection pathways [22], with beef fattening herds appearing more susceptible to infection introduced by bought-in cattle than dairy herds, and in NI, there is elevated risk of bTB infection associated with the purchase of beef animals [26]. These differences in herd management may subsequently manifest in different spatial relationships in the clustering of M. bovis in, and between, infected cattle and badger populations. We aimed to analyse spatial relationships in the M. bovis MLVA types found both in RTA badgers and cattle herds in NI to gain insight into the spread of the epidemic, both within and between hosts
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