What is a reactor?
A reactor animal is one that has shown a significant response to the tuberculin skin test. If one or more reactors are found in a herd, the herd has a “TB breakdown”.
Do all reactors have Bovine TB?
There is not a simple answer to this question. Some reactors may have only been exposed to Bovine TB, some may be infected, and some of these may be infectious to other animals. All these groups of animals will give a significant response to the skin test. Some may spread the disease further and some may not. It is not possible to distinguish between them.
Therefore they are all removed in the control of the disease as they are a risk.
TB can sometimes react to other Mycobacteria. The particular test used in NI is designed to mitigate against this. Therefore, a reaction to the test used in NI is considerably more likely to have been caused by M bovis than any other organism.
It is estimated that only 4 in 10,000 animals will be removed that have not been exposed to bovine TB.
The methods that are used to investigate the disease further are dependent on a number of factors. Some infected animals may have very small disease lesions that may not be seen at post mortem examination in the meat plant.
The subsequent laboratory examination is highly dependent on the tissue selected for further examination. If no lesions are seen, tissue that is diseased may not be selected. This significantly reduces the chances of finding the bacterium.
The TB bacterium grows very slowly. This makes growing it difficult and means that results are not available for a long time.
Given all of these difficulties, receiving a negative result at post mortem or the laboratory tests does not mean that the animal did not have TB.
What happens when I have a reactor?
There will be movement restrictions placed on your herd. DAERA will value and slaughter the reactors. Your herd will be assessed by your Patch Veterinary Officer to ensure any disease risk to you, your herd or to other herds is minimised.
What happens to reactor animals?
Reactors will be slaughtered. You must isolate them from the rest of the herd until they are slaughtered. This will reduce the risk of them spreading bovine TB on your farm. Every day that they are with the rest of your herd, there is a risk of TB being spread further. DAERA will remove reactors from your herd as soon as possible and take them to be slaughtered. At the factory, the carcase will be examined for signs of TB and samples taken for further analysis where appropriate.
How do I find out my animal’s post mortem or lab results?
Animals are examined at post mortem in the abattoir for visible evidence of tuberculosis. You can find out if TB-type lesions were found to be present in the animal by contacting your Patch Veterinary Officer. Only lesions large enough to be seen to the naked eye will have a positive post mortem result. Therefore, not finding lesions does not mean the animal was not infected.
Samples from the carcase are sent to the veterinary laboratory in Stoney Road, Belfast. Any lesion found at post mortem at the factory is examined under the microscope at the lab. Even if no lesion was found, staff at the laboratory will try to grow TB bacteria from the carcase samples. TB bacteria grow very slowly and it is likely to be eight to ten weeks before we have any results. Information is available from your Patch Veterinary Officer.
Why do a post mortem?
By examining the carcase we may see signs of disease in the animal. This helps us to give you better advice on how to reduce the risk of the disease spreading within your herd. Post mortem results help us decide how much more testing we need to carry out in your herd and in neighbouring herds, and whether we should trace animals that you have bought or sold.
What are lesions?
The term “lesion” means the damage to part of the body caused by a disease or injury. In the case of TB, lesions are most common in the lymph nodes (glands) of the head and chest, and in the lungs. They may also occur in the gut and at other sites. If lesions can be seen with the naked eye they are called “visible” lesions. Sometimes lesions may be present that are too small to be visible to the naked eye.
Occasionally we find an animal that has TB lesions widespread throughout its body.
Depending on where the lesion is, it may cause symptoms in the live animal. For example, lesions in the throat glands may cause “roaring”.
Why do some reactors not show signs of disease?
Because herds are tested at least every 12 months, disease is often detected by the test before it has had time to become visible to the naked eye.
Does “no visible lesions” mean no infection?
No. Post mortem examinations are carried out at slaughterhouses for reasons of public health, not to find TB lesions. These post mortems are much less detailed than ones carried out in a laboratory post mortem room. Veterinary inspectors examine those parts of the animal where TB is most likely to occur. They have only a limited time for that examination at the abattoir. Tissue samples from the carcase are sent to the laboratory, and TB may be seen under the microscope or grown in the laboratory, sometimes even in cases where no lesions were found. Even if TB is not found at post mortem or in the laboratory, the animal has failed the skin test and is still a reactor. Because TB lesions are not always easy to spot under abattoir conditions, the skin test remains a much more reliable indicator of disease than abattoir or lab results.
Does a TB reactor affect the slaughter of other animals in a herd?
Usually we will only slaughter animals that have reacted to the skin test. However, we may re-examine the skin test results of the animals remaining in your herd using a more severe interpretation if necessary. This frequently occurs when disease is confirmed by further positive results at post mortem or in the laboratory. This may lead to animals which had been classified as inconclusive or even negative being reclassified as reactors and removed. Also, we may feel it is necessary to slaughter other animals in the same group which have been in close contact with reactor cattle. You will receive the full market value for these animals.
How long will it take for reactors to be collected from my farm?
After valuation, the reactors will be collected as soon as possible by a haulier working for DAERA. The haulier liaises with the abattoir that will slaughter the animals. DAERA aims to have the animals removed within 15 working days, and many are removed sooner than this. This reduces the risk to your herd. If there is a delay beyond the 15 days, you may want to phone the local DAERA office to check on any progress.
What about disinfection after a reactor is found?
Mycobacterium bovis can survive in the environment quite well compared to other disease agents. Therefore environmental contamination poses a risk of further disease spread. You will have to thoroughly cleanse and disinfect all places (other than fields) where you have kept reactor cattle, and all equipment and tools you have used with them. Cleansing - that is the removal of all organic matter such as dung and bedding - is vital, as disinfectants are much less effective without it. Cleansing and disinfection will kill the TB bacterium and help prevent the disease spreading to other cattle in your herd.
You must use an approved disinfectant that has been tested for use against TB. DAERA staff will provide you with a list of approved disinfectants showing the appropriate dilution rate that will kill TB. Many disinfectants are actually ineffective against this disease, so it is important to use the right one in the right way.
A Veterinary Officer or Animal Health & Welfare Inspector will give you a notice (BT33) telling you what cleansing and disinfection you must do. The timing and the extent of the cleansing and disinfection will depend on your own farm’s circumstances. By law, you must carry out the cleansing and disinfection set out in the BT33 notice, but you can employ contractors to do the work if you want to. You should contact the Divisional Veterinary Office as soon as possible after you have finished the cleansing and disinfection so that it can be inspected.
If no satisfactory inspection of the cleansing and disinfection has been carried out, your herd will remain restricted and your herd may be required to undergo more testing.
What is an inconclusive animal?
Some animals give a reaction to the skin test which is less than the reaction which would classify them as reactors but is not a negative result. These animals must be tested again not less than 42 days after the first test. Until the re-test is carried out, these inconclusives must be isolated from other animals in the herd to avoid any risk that infection might spread.
DAERA will issue a notice (BT21) to you giving the tag number of the inconclusive animal and requiring it to be isolated. The notice also explains that the animal may not be moved from the farm unless a licence for it to move is issued by DAERA. Inconclusives will only be licensed to move directly to slaughter in a slaughterhouse within Northern Ireland.
What happens to an inconclusive animal?
Inconclusives are re-tested after 42 days and if the result is negative the restrictions on the animal are withdrawn. If the result is not negative, the animal will be classed as a reactor and be removed from the herd. The herd is then a TB breakdown and is restricted and tested in the same way as any other TB breakdown herd.
Are inconclusive animals ever slaughtered?
You may decide to slaughter an inconclusive animal at a meat plant at your own risk, with prior permission from DAERA. You might decide to do this to reduce the risk of TB to your herd, or you may want to slaughter the animal because it has reached slaughter weight. Slaughtering an inconclusive animal will usually mean having to do a whole herd test at least 60 days later as the animal itself cannot be re-tested.
During a TB breakdown, inconclusive animals may sometimes be reinterpreted as reactors, and valued and removed like any other reactor.
Density of herds with TB reactors
A map showing the density of TB reactor herds in Northern Ireland is available at the link below: