What a new bovine TB test trial in Devon means for farmers

At an undisclosed farm location in Devon, leading vet Dick Sibley, director of West Ridge Veterinary Practice in Tiverton, is trialling a novel TB management package, including two new tests, which he thinks could play a role in the battle against TB.

Working with a large commercial dairy herd that has been under restriction for more than six years, the total package involves both the detection and control of the disease in the cattle as well as management of the disease in the local badgers, with the help of Brian May’s Save Me Trust.

See also: How a beef enterprise has adapted to overcome TB

Mr Sibley says these novel tests are not the solution to TB and won’t cure anything, but are a research tool to discover hidden infections and transmission routes.

1. The phage test, developed by microbiologist Cath Rees of Nottingham University, which has been detecting bovine TB bacterium in cows much more accurately than the skin test currently used.

2. The phage test is followed by a qPCR test, developed by Liz Wellington, life sciences professor at Warwick University, which detects bTB in faeces to determine whether a cow is “shedding” the disease. On the trial farm, if a cow is found to be spreading the disease, it is culled.

“Please be aware that it is an offence to test a bovine for bTB without the permission of the secretary of state, and it is also an offence to use a non-approved test,” says Mr Sibley.

“We have been working with the close co-operation and support of the APHA vets and field staff, who have been extremely helpful in this project. But don’t do this at home.”

Farmers Weekly asked Mr Sibley about the tests and their scope for use on farms across the UK.

What do these two new tests you are trialling offer that the current bTB test doesn’t?

These tests look for the actual organism that causes bTB – Mycobacterium bovis. The current approved tests – the skin test, the gamma interferon blood test and the Idexx Elisa blood test – all look for the animal’s response to exposure to the organism, rather than the organism itself.

Thus, they all have weaknesses. The skin test in particular can miss heavily infected cows that are infectious – shedding the organism.

Many farmers have had experience of a barren cow being found to have TB in the slaughterhouse just a few weeks after being skin tested negative – an indication that the test can miss some cows.

What results have you found using them on the trial dairy farm?

We have found numerous cows (about 80 in total) that have been skin tested on many occasions and not been deemed as “reactors” that have tested positive to the phage test – suggesting they are infected.

The phage test finds the organism in low numbers in their blood cells.

Although these animals are infected, most are not infectious – they are latent carriers.

However, several are also positive on the qPCR test, where we have found large numbers of organisms in their dung – these animals are not only infected, but they are also infectious. We call them “shedders”.

Interestingly, we looked in the saliva of 60 or so cattle, and did not find the organism there in any of them.

You told the Guardian you think these tests could reach the farmer’s toolbox in five years. How can they be scaled and rolled out?

The tests have limited application – most herds clear up fast and effectively with the current skin test, and sometimes the gamma interferon.

Indeed, most countries have eradicated bTB using these current tests. However, there are certain situations where these different tests are needed – more sophisticated tools are required from the toolbox.

As an analogy, you only need an allen key and a screwdriver to assemble a kitchen unit, but you need more subtle and sensitive tools to make a bespoke kitchen.

How expensive are these tests to carry out now and would they be expensive to roll out? Do you foresee them being government-funded, as the current whole-herd compulsory test is?

 I am not sure about the commercial cost. We have been generously supported by the universities to prove the concept of their use, but the costs may be irrelevant compared with the economic costs to the farms where they will be most useful – the chronically infected larger herds that suffer both direct losses from culled cows and indirect losses through the trading restrictions imposed by being infected.

What else do you think farmers need to do in the battle against TB? Are you trialling preventative measures at the trial farm as well as the new tests?

Yes, absolutely. These tests are just a small part of an overall TB management plan that we have implemented in the herd.

The whole idea is to prevent new infections, and we have looked at every possible route of transmission and tried to block it. We are taking a risk-based approach to disease management.

We are managing the disease very much like Johne’s (they are very similar diseases caused by a very similar organism). We have also looked at environmental challenges and found 30% of the badger faecal samples from badger latrines on the farm were infected with bTB, and so we have had to address this risk as well.

Tests do not cure the disease, so how do you think they would help in getting rid of disease? Do you think we need a vaccine that works and is cost-effective for this to be possible?

The tests simply identify cattle that are infected, and that then go on to be infectious.

We are about to use another test to see if we can predict which infected cattle are likely to become infectious, and thus be a danger to the rest of the herd. As long as they are just infected without being infectious, we are not too worried about them.

Vaccines for cattle are a long way off, and although they might be useful, we have controlled plenty of diseases without the use of vaccines – did we ever need to vaccinate against BSE? Indeed, did we ever have a test for BSE?

Many farms have controlled and eradicated Johne’s disease just using these techniques, so it should be possible with bTB. Where these tests might help, if cattle vaccines ever do come along, is that they can spot an infected cow if it is vaccinated or not: the vaccine should not interfere with these tests, unlike the current skin and gamma tests.

How far away do you think the UK is from getting on top of the disease?

How long is a piece of string? But what I do know is that until everyone pulls in the same direction, understands the sources of infection and the routes of transmission, and blocks those routes to prevent new infections, we will never win.

At the moment, for every herd we clear up, a fresh one goes down, and so we will never win. The key to infectious disease control is to prevent new infections – period. Prevention does not mean testing – prevention is using biosecurity and biocontainment to prevent disease entering a herd and spreading within that herd.

What about other disease vectors? What do you think needs to be done about them in the long term in order to reduce the spread of the disease?

There is an undoubted reservoir of infection in wildlife, as we have demonstrated on this farm. This creates an environmental source of infection, particularly in the grazing pastures. We cannot tackle the disease in the cattle without dealing with the environmental risks – so we are.

We have acquired vaccine and there is no real shortage – if you pay, they will make it. The Irish have been very helpful in helping us to secure a supply, as they have been using vaccine effectively for several years.

The import and use of the BCG vaccine is under strict controls and licensing requirements, but we have had co-operation from the VMD, APHA and Natural England to get the vaccine and be able to use it effectively.

In the end, if we roll this programme out over other farms and larger areas, we will probably use a combination of culling and vaccination. If we can demonstrate that vaccination works in reducing the environmental challenge, then I can’t see why the “culling zones” can’t be redefined as “bTB management zones” and farmers and landowners are given the option to cull or vaccinate as part of an overall bTB management programme.