It has been known for some time that the skin test for BTB loses sensitivity when cattle are infected with liver fluke. In a paper published last week (Fasciola hepatica is associated with the failure to detect bovine tuberculosis in dairy cattle) www.nature.com/ncomms/journal/v3/n5/full/ncomms1840.html it is claimed that the loss of sensitivity may be so high that one third of infected cattle are not being detected in areas with high liver fluke occurrence. The authors go on to suggest that this may be causing entire areas, not just individual cattle or herds, to be falsely deemed of low incidence, with resultant spread of infection.
Rethink suggest that a further factor in the spread of BTB has been unmasked – the unwillingness of Defra to consider evidence if it upsets established views. Instead of hurrying to study the paper and consider the implications, Defra have (according to the BBC www.bbc.co.uk/news/science-environment-18118124 ) dismissed the research adding:
"The absence of positive cases of bovine TB in some areas co-inciding with large amounts of liver fluke cannot be used to claim liver fluke is hiding cases, as cattle carcasses are inspected in abattoirs and we would see evidence of TB in the slaughtered animals if this was the case."
If they had read the paper they would realise that is only part of the argument, and anyway other work quoted by the authors has suggested lesions may also be suppressed.