Thursday, July 03, 2014

Cull the Cattle - Simples

Once again we can thank mathematical modelers for some hair raising conclusions - [link] obtained from the latest load of guff data entered, together with a generous sprinkling of mathematical symbols, into their new toy. The Guardian -[link] gleefully explores the story with the headline, Mass Cull of Cattle is required to control TB.

That sort of carnage was tried in 2001 for FMD, again using a rampant computer model if we remember correctly - but let that pass.

And we do not propose to remind readers of past efforts - [link] to control zTB with cattle controls alone. Or the effect on the incidence cattle disease if the maintenance reservoir -[link] of disease is removed. Or even the amount of bacterial contamination a single badger - [link] can generate, and how little of that 'contamination' is required to provoke a skin test reaction in cattle.

 Having relied so much on the 'rough assumptions' contained in models developed by the ISG, we won't remind the authors of this work -[link] which cost an eye watering £2.8 million, but failed to get any samples from salami sliced reactor cattle to provide evidence of onwards transmission of zTB.

And we will we do no more with this paper than point to this paragraph which describes its data input - or lack of it.
The role of badgers in the maintenance and spread of bovine TB is a matter of considerable scientific, political and public interest5, 25, 26. Owing to the absence of necessary spatial and population level data on badgers, our model does not explicitly include their role in transmission. The environmental reservoirs play a comparable function, although the contribution of reservoir species and contaminated pasture cannot be separated. The environment is essential in maintaining local infection and may be implicated in up to 80% of all herd breakdowns (Fig. 2b, green hashed area).
We have no computer model set up to ignore badgers, so we will stick to the basics.  Not of mathematical models, but epidemiology and disease control.

No disease control program in a target species can be successful if a maintenance reservoir in an interacting species is left to re infect. That is indisputable. Just as the self sustaining nature of zTB in the badger is indisputable. And ignoring it does not make it disappear.

No comments: