Monday, January 04, 2010

Badgers v. cattle. Relative contributions to disease transmission.

After our posting on the relative infectivety of bTB lesions in cattle, badgers and other mammals, a comment alerted us to work done outside the ISG box, which sought to match the attributed cause of a TB breakdown to either cattle or wildlife. The model used for this exercise found that just 16% of bTb breakdowns in 2004 were directly attributable to cattle movements.

The following is part of the abstract from the paper "Estimates for Local and Movement-based Transmission of Bovine Tuberculosis in British cattle" (Green et al) which was published in 2008.
"Both badgers and livestock movements have been implicated in contributing to the ongoing epidemic of bovine tuberculosis (BTB) in British cattle. However, the relative contributions of these and other causes are not well quantified. We used cattle movement data to construct an individual (premises)-based model of BTB spread within Great Britain, accounting for spread due to recorded cattle movements and other causes.

Outbreak data for 2004 were best explained by a model attributing 16% of herd infections directly to cattle movements, and a further 9% unexplained, potentially including spread from unrecorded movements.

The best-fit model assumed low levels of cattle-to-cattle transmission.

The remaining 75% of infection was attributed to local effects within specific high-risk areas."
We love the pseudonym 'local effect' - excellent.
And this analysis ties in quite nicely with that of actual herd breakdowns in the SW of England, described in our posting here and illustrated with charts of actual bTB breakdowns in Devon, over the same period.

We are already hearing of breaches both north and south in Defra's bTB 'maginot' line. This was an area crayonned in red, which sought to isolate TB to the west of a line on a map, with a 2 km buffer zone on its eastern edge. Pity no one told the 'local effects not to cross it.

The full paper from which the abstract was taken, can be viewed on this link. (Ed- the link may need a second click as it opens, and a further 'OK' to ignore hieroglyphics.)

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