Abstract
BackgroundBovine tuberculosis (bTB), caused by Mycobacterium bovis, is an important livestock disease raising public health and economic concerns around the world. In New Zealand, a number of wildlife species are implicated in the spread and persistence of bTB in cattle populations, most notably the brushtail possum (Trichosurus vulpecula). Whole Genome Sequenced (WGS) M. bovis isolates sourced from infected cattle and wildlife across New Zealand were analysed. Bayesian phylogenetic analyses were conducted to estimate the substitution rate of the sampled population and investigate the role of wildlife. In addition, the utility of WGS was examined with a view to these methods being incorporated into routine bTB surveillance.ResultsA high rate of exchange was evident between the sampled wildlife and cattle populations but directional estimates of inter-species transmission were sensitive to the sampling strategy employed. A relatively high substitution rate was estimated, this, in combination with a strong spatial signature and a good agreement to previous typing methods, acts to endorse WGS as a typing tool.ConclusionsIn agreement with the current knowledge of bTB in New Zealand, transmission of M. bovis between cattle and wildlife was evident. Without direction, these estimates are less informative but taken in conjunction with the low prevalence of bTB in New Zealand’s cattle population it is likely that, currently, wildlife populations are acting as the main bTB reservoir. Wildlife should therefore continue to be targeted if bTB is to be eradicated from New Zealand. WGS will be a considerable aid to bTB eradication by greatly improving the discriminatory power of molecular typing data. The substitution rates estimated here will be an important part of epidemiological investigations using WGS data.
Highlights
Bovine tuberculosis, caused by Mycobacterium bovis, is an important livestock disease raising public health and economic concerns around the world
The current research suggests that M. bovis infection was being transmitted between the sampled wildlife and cattle populations
With New Zealand’s low prevalence of Bovine tuberculosis (bTB) in livestock, despite being unable to estimate inter-species transmission direction in the current research, it would seem highly likely that wildlife populations are acting as maintenance reservoirs and as such should remain the target of the eradication campaign
Summary
Bovine tuberculosis (bTB), caused by Mycobacterium bovis, is an important livestock disease raising public health and economic concerns around the world. In New Zealand, a number of wildlife species are implicated in the spread and persistence of bTB in cattle populations, most notably the brushtail possum (Trichosurus vulpecula). Whole Genome Sequenced (WGS) M. bovis isolates sourced from infected cattle and wildlife across New Zealand were analysed. Control of bovine tuberculosis (bTB) in domestic cattle herds is motivated by the zoonotic risk of the causative agent Mycobacterium bovis, its impacts on animal productivity, and the benefits of TB-free status in. In New Zealand, the introduced brushtail possum (Trichosurus vulpecula) has long been recognised as an Crispell et al BMC Genomics (2017) 18:180 important maintenance reservoir for M. bovis [9, 10]. Control of bTB in cattle herds uses test and slaughter surveillance; more frequent testing and movement control are employed in Vector Risk Areas (VRAs), where the risk of infection from wildlife is highest [11]. The incidence of infected cattle herds has been drastically reduced over the last two decades [13] but complete eradication remains elusive, likely as a result of persistent infection in wildlife populations
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