Team:Exeter/DickSibley
Richard Sibley
Principal Vet and Director of West Ridge Veterinary Practice Ltd
We decided to visit a veterinary practice where we met with the director, Richard (Dick) Sibley, a highly respected vet with over 30 years experience across a wide range of veterinary practice. Dick and his practice have worked extensively with bTB, ranging from testing cattle through to offering bTB free programmes to farmers. After we outlined the concept of our Riboswitch, he explained more about the current bTB detection system, recent research into the disease and the work his practice does to tackle bTB. Below are the main points that Dick made us aware of at the start of our project.
Persistency and Contagiousness
Dick introduced some important concepts to us as a team. Firstly was the R0 value of Bovine TB (bTB) in cows. R0 is the disease reproduction number and is a mathematical way of explaining how contagious an infectious disease is. Although it can be hard to determine exactly, current research estimates the R0 value for TB in cows ranges from 1.0 - 4.9. This means one infectious cow has the ability to infect up to 4 other animals meaning the transmission rate can be extremely high. Combine this with the close conditions farm animals are kept in, bTB spread throughout a herd is fast. Under the current bTB testing law, if a farm experiences a breakdown it has a 60 day period until a second test is conducted. Any false negative individuals that have been left in a herd from the first test won’t get a chance to be detected for 60 days - more than enough time for those individuals to transmit the disease.
Mycobacterium bovis (M.bovis) is a very challenging pathogen. Not only is it incredibly difficult to treat, it has the ability to persist in the environment for months. Dust, etc etc are just some of the things that the bacterium is able to survive on. Clearly this creates a very challenging situation for both farmers and vets trying to eradicate bTB. If a farm is finally declared bTB free status, any area of the farm that may have been exposed to an infected animal (silage, buildings, equipment) may be able to transmit the infection back into the herd. Dick explained how some farmers face a situation where they have to isolate their entire farm, keep the cattle indoors and follow a strict regime to minimise the risk of bTB exposure. Also, Dick made us aware of some current research into the ability of M.bovis to persist in the environment.
Herd Size Increase and Sensitivity Issues
Advances in technology has led to a huge increase in the size of farms in the UK. Not only has the number of cattle increased as a whole, the size of individual herds has also greatly increased. In 1996 the average size of a UK dairy herd was 75 cows. In 2014 this had increased to 133 cows. Increase in herd size has highlighted how the current Tuberculin skin test is simply not sensitive enough to allow for a strategy to eradicate bTB in the UK, as shown by the larger dairy farm herds, where recurrent bTB breakdowns are common. Dick highlighted how the current Tuberculin skin test can leave behind cows that are infectious and that in current farming conditions leaving behind even a single infectious animal can lead to bTB breakdown. Large high risk herds are particularly challenging to achieve bTB free status. Dick made it clear that our test would be most useful not as a stand alone, but as a tool that could be used in conjunction with the current test to achieve greater specificity in these high risk large herds.
Points to Consider
Our multiple meetings with Richard (Dick) Sibley helped us as a team understand exactly what situation the UK currently faces with eradicating bTB. Dick made it clear to us the situation of bTB in Devon and Cornwall. With 1.8 million animals tested in Devon and Cornwall in 2014 and 800 farms under bTB restriction, the problem our test is trying to solve is very relevant to our local area.
As well as highlighting some of the fundamental problems with the current Tuberculin skin test, Dick helped us gain an understanding of how our test might best be applied in the field.
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