Officially tuberculosis free status and the Dairy Products (Hygiene (Scotland) Regulations 1995
Friday 12 October 2001
This guidance note provides information and advice to Food Authorities in Scotland who have dairy herds and/or dairy establishments in their area which produce unpasteurised milk-based products
Introduction
The purpose of this guidance note is to provide information and advice to Food Authorities in Scotland who have dairy herds and/or dairy establishments in their area which produce unpasteurised milk-based products, and who therefore may be involved in investigations following notification from the State Veterinary Service (SVS) of the loss of 'Officially Tuberculosis Free' (OTF) status of dairy herds.
Mycobacterium bovis infection in cattle
Most human tuberculosis is caused by the bacterium Mycobacterium tuberculosis. This can infect cattle but rarely causes clinical disease.
Tuberculosis (TB) in cattle is caused by Mycobacterium bovis (M. bovis). Bovine TB can affect other species (such as deer and badgers). Human infection can also occur i.e. the bacteria may be inhaled in aerosols from the lungs of infected cattle, or ingested through consuming unpasteurised milk-based products made from affected milk. However, with regular testing of herds, slaughter of reactors and compulsory pasteurisation of drinking milk in Scotland, human cases are relatively rare and usually thought to be due to the reactivation of disease contracted earlier in life (i.e. before compulsory milk pasteurisation), from infection contracted abroad or spread from person to person.
In recent years, TB in cattle has increased in England and Wales in both the numbers affected and geographic spread. Since the early 1980s, the number of herds reported each year where the OTF status has been withdrawn has steadily increased. Initially this mainly affected the South West of England although in recent years this has spread to parts of South Wales and the West Midlands. There has been no increase of TB in Scotland.
The routine tuberculin skin testing of herds is a key part of TB control in cattle in the UK. Any animal showing a positive reaction (i.e. a "reactor") to this test is slaughtered and compensation paid. Slaughtered reactors undergo post-mortem examination, and tissue samples are collected for culture of the organism. Less than half of reactor cattle are found to have visible lesions or a positive culture for M. bovis. The Meat Hygiene Service also routinely examines all carcasses at abattoirs for macroscopic lesions of TB as part of general meat inspection.
The Dairy Products (Hygiene) (Scotland) Regulations (DPHSRs) 1995, require that raw cows? milk and raw buffaloes? milk must come from animals belonging to a herd which is OTF. Milk which does not satisfy this condition may only be sold for human consumption after it has been heat-treated, as the bacterium is destroyed by pasteurisation. The State Veterinary Service (SVS) will notify Food Authorities of the conditions in a herd, which have resulted in the loss of OTF status (reactors to a skin test, or tuberculous lesions detected in a slaughtered animal).
PART A - Animal Health
Routine testing of herds
Testing for TB is carried out in Scotland on behalf of Scottish Ministers by:
- Veterinary Officers of the SVS
- Local Veterinary Inspectors (LVIs) (private vets appointed to carry out statutory duties)
Where individual farmers have agreed with the local Divisional Veterinary Manager (DVM) to pay for private TB testing, the farmer is required to notify the DVM of the results. Farmers may wish to carry out private tests on newly purchased animals, to clarify their TB status. Also, more frequent testing may provide an early indication of problems for producers of raw milk-based products.
The frequency of TB testing is based on EU Directive 64/432 but can be varied locally by the DVM.
Most herds are tested every four years, but where the risk of disease is considered greater, or where the prevalence of disease is high, testing is carried out more frequently.
Food Authorities should liaise with DVMs to ensure that herds supplying processors manufacturing unpasteurised dairy products are tested annually. Food Authorities should notify DVMs when they become aware of the production of unpasteurised dairy products in their area. Food Authorities should advise manufacturers producing unpasteurised dairy products to check that the milk they purchase comes from dairy herds which are tested annually for TB. Food Authorities should contact the DVM if there are any concerns about these issues.
Food Authorities may find it helpful to liaise with Local Authority Animal Health and Welfare Inspectors, as their responsibilities include checking farm records under animal health legislation.
Finding a TB reactor
When the disease is suspected (reactors or slaughterhouse cases) and OTF status is suspended The DVM will send a written copy of the herd restriction notice to the relevant Head of Environmental Services (HES).
When reactors are slaughtered and herd restrictions applied, the DVM will make arrangements to re-test the herd at 60 day intervals until negative herd tests are obtained (one clear test when disease has not been confirmed, two tests when infection has been confirmed). Restrictions on the movement of the herd will be lifted and the OTF status restored following a programme of clear skin testing. The DVM will notify the HES when OTF status has been regained.
Laboratory confirmation of TB
Laboratory confirmation of TB by culture will take a minimum of eight weeks and may take longer if the samples are contaminated. TB is often confirmed on the basis of characteristic lesions being present at post-mortem examination of slaughtered reactors.
HESs are notified of all reactors (whether later proved to be infected or not) in dairy herds for dairy hygiene purposes. The Consultant of Public Health Medicine (CPHM) is notified of confirmed disease in any herd for human health screening purposes.
Inconclusive reactors
Occasionally, animal skin test results will be in an intermediate range between positive and negative. These animals are classed as inconclusive reactors (IRs). In herds where there is no recent history (within the last three years) of confirmed TB, such animals are isolated and restricted and re-tested after 60 days. There are no restrictions regarding milk from these animals and the OTF status of the herd is not compromised. If the inconclusive cattle re-test negative, the DVM will permit the animal to rejoin the herd. If they re-test positive they are classed as reactors and the procedures laid out in Part A Section (ii) are followed.
In herds where there has been recent evidence of TB, disclosure of IRs result in the whole herd being placed under restrictions and the OTF status suspended. HESs will be notified of these situations.
If after re-testing the results are still inconclusive, the animal(s) will be slaughtered as positive reactors and a post-mortem examination carried out at the slaughterhouse. Samples will be sent for culture.
PART B - Human Health
Unpasteurised milk-based products
In Scotland the SVS will notify Food Authorities of conditions on a dairy farm that result in the loss of OTF status. Investigations should be initiated by the Food Authority based on this notification, to find out if milk from the herd is being used to make unpasteurised milk-based products, either on the particular farm or elsewhere.
Enforcement Officers need to:
- liaise with the first buyer of the milk to establish where the milk from the affected herd is being transported and delivered to;
- confirm the use of the milk;
- ensure that the milk and any milk with which it may be mixed, will receive adequate heat treatment.
This may involve liaison with other food authorities, including the home authority of the first buyer where appropriate.
Notification of loss of OTF status should immediately alert the enforcement officer to ensure that the milk from the suspect herd is heat treated and that raw milk-based product production continues only with milk supplied from an OTF herd.
Where the affected farm has heat treatment facilities installed, the Food Authority should confirm that all hazard analysis controls are in place and working effectively, including adequate heat treatment.
If a Food Authority becomes aware that raw milk products have already been produced or are being produced from a herd where the OTF status has been lost, the risks to human health should be assessed locally in liaison with the CPHM and the DVM. Advice should/can also be obtained where necessary from the local Scottish Centre for Infection and Environmental Health (SCIEH) and decisions will be based on individual circumstances. In the case of manufacture of raw products from the milk it is likely that factors to be taken into account will include:
- Bovine TB can cause serious harm especially in young children although cases are rare.
- TB bacilli can sometimes be present in milk even in the absence of obvious udder disease.
- Herd history.
- If the herd is in a high-risk area for bovine TB.
- The positive reaction to the skin test.
- The number of cattle in a dairy herd which tested positive.
- The health of the reactor cattle.
- Evidence of active TB found during post-mortem.
- Type(s) of milk-based product and production processes and any scientific evidence that these may eliminate the pathogens.
- Batch size/quantity of product, its? distribution, shelf life (by the time a report is received about lesions, following the post-mortem, the shelf life of batches of the product may have been exceeded).
Where there is evidence of active disease in an animal, then it is likely that withdrawal of batches of the product produced before the date of sampling would be advocated as a precaution. It would, however, still be open to the producer to provide scientific evidence where he/she believes that the production process would eliminate pathogens and that TB organisms are absent from the product.
If further advice is required, please contact the Food Standards Agency, Scotland, telephone (01224) 285137; fax (01224) 285168 who will work with the local investigation team. Advice will depend on the circumstances of the incident, including the factors outlined above.
Cases of human illness
In the event of a CPHM being notified that a person(s) has confirmed bovine TB, and the infection is thought to be recently acquired, the CPHM should ascertain any connection with cattle that might indicate the infection could have been caught from an animal source or could be passed to animals. If so, they should inform the Food Authority. If there is a risk that a herd and/or other farm stock could be infected then the Enforcement Officer should notify the DVM so that checks can be made on the herds. It may also be appropriate to notify other relevant Food Authorities, local farmers, dairies and producers, milk buyers or distributors that might be affected (with due regard for patient confidentiality).
For detailed guidance on dealing with human cases or contacts please refer to 'The Control of Tuberculosis in Scotland (1998)'. For copies of the guidance, please contact Department of Health, telephone (0131) 244 2278.
If more information on SVS procedures concerning TB controls in cattle within Scotland is required, please contact your Local Divisional Veterinary Office.
Food Standards Agency (Scotland)
6th Floor
St Magnus House
Aberdeen
AB11 6NJ
28 June 2000