An insight from New Zealand microbiologist, J M O'Donnell, working in the field of immunology we post below, particularly in the light of the ISG's conclusion that bearing down on the disease only in cattle, will have a disproportionate effect on overall disease incidence if the wildlife reservoir left.
Commenting on the Gilbert study of cattle movements, Mr. O'Donnell says:
This study could also be interesting to contrast with the known spread of BTB in general regions. As it predicts BTB spread based on cattle movements, it does immediately present a means to experimentally verify it on the ground (so to speak). Given their model, it should be expected that movements from areas with BTB should be associated with the detection of certain Mycobacterium bovis spooligotypes (basically strains). This is because the imported infected cattle should bring with them their M. bovis types and therefore spread that to the uninfected herd. Over time, based on what cattle movements went into a region and what spooligotypes infected cattle bought with them, you would expect to see those spooligotypes in subsequent herd breakdowns.
Here is where I become somewhat skeptical. It’s known from previous experiments which have analysed the spooligotypes of M. bovis from badgers and cattle that these tend to be shared between the two species (see part III). This also tends to be isolated by geographical regions, with a mixture of spooligotypes but only a few ‘oddball’ ones that aren’t shared between badgers and cattle. In the model predicted by Gilbert et al., 2004, where cattle movement is the primary motivator for BTB spread it also implies cattle to cattle spread. The lack of spooligotype mixing between regions from studies conducted in Ireland (for example) have shown spooligotypes of M. bovis tend to be similar in a region but not between them, raises concerns over cattle movement as a predictor of M. bovis. It may be likely that cattle movement helps to spread the infection to a new region, but is not sufficient to determine if the disease will be able to establish in the new region.