January 16, 2021

I, Science

The science magazine of Imperial College

Bovine TB rates are much higher than estimated

Bovine Tuberculosis (BTB) has become a devastating problem for British farmers, resulting in the slaughter of around 25,000 cattle last year, at a cost of more than £90 million to the taxpayer. But despite the eradication strategy pushed forward by the government, BTB infection rates continue to rise and the disease persists in spreading.

Several contributing factors have been identified, including cattle movements and reservoirs of infection within wildlife species, such as badgers. In December, this led to the government implementing less than popular plans to tackle the spread of BTB through badger culling, despite years of fierce debate on the lack of scientific evidence behind the proposal, and fears raised by scientists that culling could in fact increase BTB rates.

Now the government’s evidence base for its BTB eradication programme has been dealt another blow, as new research published last month shows major errors in the estimation of BTB incidences – figures which have been used to inform control policies.

In a study of more than 3,000 British dairy herds, scientists at the Universities of Nottingham and Liverpool discovered that a parasitic flatworm found in over 70 per cent of cattle, the common liver fluke, reduces the sensitivity of skin tests used to diagnose BTB in the animals, effectively masking the presence of the disease.

“This certainly puts a question mark over the current reported rates of incidence,” says Dr Robin Flynn, from the University of Nottingham, and co-author of the research. “We estimate that around 30 per cent of animals are being misdiagnosed using the current skin test.”

This new evidence that cattle BTB rates are much higher than current estimates suggests that transmission from infected cattle to other cattle and wildlife reservoirs has a much greater role in spreading the disease than previously thought. Badger culling may therefore not be the panacea it has been argued to be.

The approval of badger culling could instead be considered to be enormously beneficial for the government in being seen to proactively deal with the concerns of farming communities and responding to pressure from the farming lobby – a group that appear to be fully convinced of the badger-BTB link despite uncertainties, and that have long wanted to rid themselves of the damage-causing ‘pests’ anyway.

However, the more the reliability of the evidence is called into question, the more urgent the need to properly address the issue. Following this new research, the government may now need to finally give the farming communities what they need to tackle the disease, by focusing resources on developing more effective skin tests, ensuring robust disease monitoring, and implementing an evidence-based policy that can realistically eradicate the disease.

Image: flickr | publicenergy