For most people, TB, or tuberculosis, is something that happens in the countryside, affects cows, is spread by badgers and causes lots of arguments. These are all true. But to those involved with TB control in the UK, it means a whole lot more. 

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What is TB?

Tuberculosis (TB) is a bacterial disease that typically affects the lungs and causes respiratory symptoms. But it can also affect many other parts of the body. Some people may be familiar with TB from having a BCG vaccination, and it is thanks to this regime that rates of TB in the UK population are very low. 

The history of tuberculosis and cattle

Tuberculosis in cows has been a national problem in the UK since the start of the 20th century. It is a zoonotic disease meaning it can transmit from cattle to people. Therefore, it became a major human health concern. Testing of cattle was first developed in the 1920s but it wasn’t until 1950 that it became compulsory in the UK to test all cattle and slaughter any reactors. At first, this test and cull method was a great success and TB was very nearly eradicated from the cattle population by the mid 1970s. 

However during the 1980s, numbers rose once again and have continued to do so to this day. Badgers are often blamed for the spread of TB to cattle in the UK and they have certainly been the focus for TB control in recent years. Badgers definitely carry bovine TB and will excrete it in saliva, nasal secretions, urine and faeces as they wander around farmyards and grazing fields. 

But many infections also arise from direct cow to cow spread, movement of cattle across the country, spreading of infected slurry and even spread on fomites such as farm machinery or farm workers. Other species of animal such as deer and alpacas have been shown to carry tuberculosis quite commonly, though the risk of them transmitting the disease to cattle herds is unclear. 

How do you test for TB?

Interestingly, the intradermal skin test used today has remained practically unchanged since it’s development in the 1920s. It involves taking measurements of the skin thickness at two specified sites on the neck of the cow. Next, injecting a small amount of avian tuberculin as a control at one site and a small amount of bovine tuberculin at the other site.

Three days later, the tester returns to re-measure the skin thickness at the two sites. If there is an increase in the thickness of the skin at the site where the bovine tuberculin was administered and this is greater than any increase in thickness at the site where the control was administered, then the animal is classed as being either a reactor or an inconclusive reactor depending on the degree of difference. 

All reactor cattle must be slaughtered as soon as possible. The whole herd will be placed under restrictions and require months of further testing. Inconclusive reactors must be isolated from the rest of the herd then retested after 60 days. There are also blood tests available that can be used to diagnose further cases in certain circumstances. 

What is TB testing like from a vet’s point of view?

As a vet, we go through at least five years of hard training to learn how to diagnose and fix sick animals. Sometimes, unfortunately, this isn’t possible and euthanasia may be the only option. However, normally this applies to very elderly or very ill animals in order to prevent any further suffering. 

Being a vet carrying out TB testing is very different. 

Yes, you are diagnosing. When a cow tests positive to the skin test, there is an extremely high chance it is a true result and the cow does indeed have TB. But, in the majority of cases, they appear outwardly healthy, yet you must condemn that animal to slaughter. There are obviously good reasons for doing so; to help prevent that animal becoming ill with the disease and eventually dying, to help stop the spread to other cows and to protect human health. 

So why can’t we treat them? 

Treatment of TB in humans is complicated, long and very costly. It is just not practical or economical to do this for cows. In 2013, it was estimated that for cases of TB that were sensitive to the usual drugs, a course of treatment for an adult human was around £5000; for cases of TB that had become resistant to the drugs, that rose to £50,000-£100,000.

A course of treatment usually takes between six and nine months. So legally, the only thing we can do for the cow is to tag it and instruct the farmer to arrange the slaughter. The disease also does not discriminate. From 6-week old calves, to pregnant heifers and from top-class breeding bulls to rare breed best-in-show winners, they must all go. 

The human cost

To have to turn to that farmer, who quite often is a friend as well as a client, and tell them that the cow in the crush is a reactor is horrendous. We can measure and re-measure and triple check the numbers but there’s no changing the facts. Quite often, there will be more than one reactor found during a test; sometimes a huge proportion of the herd can succumb. Some lose them all. 

Farmers love their cows, they work with them all day every day, and to lose any can be emotional. But it’s also a huge blow to their business, their livelihood. Finding a reactor sets in motion a schedule of events that will normally leave the farmer unable to buy, sell or move any cattle for at least 4 months. 

The rest of the herd will need to undergo two further skin tests, 60 days apart and only then if they go clear at these tests, will the restrictions be lifted. Some farms must also have a third test after a further 6 months before going back onto routine testing. If, at any point, further reactors are found, the clock starts again. 

In many cases, this means the farmer’s finances are severely hit and they just cannot operate the farm as they need to. Many farms are stuck in a continuous cycle and struggle to break free. When a breakdown occurs, there are also limitations placed on the sale of milk and the whole farm must be proved to have been thoroughly disinfected before any restrictions can be lifted. 

The stress of the test

Testing itself is time-consuming and costly. Often taking all day, or even needing to be spread over multiple days, requiring extra manpower and being physically and mentally demanding for all involved. In some cases, the cattle will also need to have blood tests done alongside the skin test. This adds further logistical problems. 

Personally, the main thing I find frustrating about TB testing is the feeling that it’s just not making a massive difference. We find reactors, they get culled from the herd, the herd are tested again and more reactors are found. Sadly, these days, it’s more of a surprise when a herd finally goes clear. 

Testing must also be carried out no matter what the weather! I’ve done tests that involved running around a field in full waterproofs and in the middle of a summer heatwave attempting to round up some rogue Dexters. I have also tested in snow that reaches the tops of my wellies, at well below zero, where I had to get a lift to the farm in an all-terrain vehicle as the roads were nearly impassible. Then there is the dreaded rain. It turns your paperwork to mush and means you’ll have to peel the pages apart, spread them all over the practice radiators when you get back and hope that your writing remains legible. 

However, TB testing does have a good side believe it or not. 

As mentioned before, a lot of the farmers become friends over the years and TB testing days can be very sociable occasions. If we’re lucky, we might get a cup of tea and maybe a chocolate biscuit too, whilst thawing out in the farmhouse kitchen. And on those rare days where the sun is shining, all the cattle behave themselves and the herd goes clear, there is nothing better. 

So how can we improve the situation?

Well hopefully, there is help on the horizon. Last year, the go-ahead was given to start field trials of a tuberculosis vaccination in cattle. The problem with doing this before was that the skin test couldn’t differentiate between an infected cow and one that had been given the vaccination. So a new skin test has had to be devised. 

Further controls, particularly around spread by wildlife, biosecurity, pre-movement testing of cattle and general surveillance will still need to be done but this is a major breakthrough in the fight against this awful disease.

Scotland has been officially free of TB since 2009. This new strategy will hopefully allow the other devolved governments to achieve their targets of eradicating bovine TB in England by 2038, in Wales by 2041 and in Northern Ireland within the next three to four decades. 

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