The phylogeny and population structure of Mycobacterium bovis in the British Isles

- The British Isles is dominated by the same major lineage of the Mycobacterium bovis bacillus.
- This lineage entered one territory and spread by the movement of infected cattle.
- This led to the development of an homogenised population.
- Recent introduction of movement controls may have led to isolation of territories.
- Isolation may have underpinned the evolution of region specific variants.

To further understand the epidemic of bovine tuberculosis in Great Britain, Northern Ireland and the Republic of Ireland, we identified 16 mutations that are phylogenetically informative for Mycobacterium bovis strains from these regions. We determined the status of these mutations among a collection of 501 strains representing the molecular diversity found in these three regions of the British Isles. The resulting linear phylogenies from each region were concordant, showing that the same lineage of M. bovis was present. The dominance of this lineage is unique within Europe, and suggests that in the past the populations were homogenous. Comparison of approximately 500 strains isolated in 2005 from each region by spoligotype and 5 locus VNTR profiling, revealed distinct differences in the genotype frequencies and sub-lineage makeup between each region. We concluded that whilst each region shared the same major phylogenetic lineage of M. bovis, more recent evolution had resulted in the development of region-specific populations. Regional differences in the M. bovis populations suggest that it may be possible to identify the movement of strains from one region to another.