Animal by-products: Q & A on M.paratuberculosis / Johne’s Disease / Crohn’s Disease / Future Policy
- Mycobacterium avium sub-species paratuberculosis (Map )
- Johne’s Disease
- Crohn’s Disease
- Future Policy
Section 1: Mycobacterium avium sub-species paratuberculosis (Map)
Q1. What is Mycobacterium avium sub-species paratuberculosis (Map)?
A1. Mycobacterium avium sub-species paratuberculosis (also called M. paratuberculosis or Map) is a bacterium pathogenic to animals that is primarily found in the digestive tract of wild and domestic herbivorous (grass eating) animals throughout the world. It has been known for many years to be the cause of Johne’s Disease in cattle, sheep, goats and other ruminants and some camelids, i.e. llamas. It also affects other animals, e.g. rabbits, pigs and horses.
M. paratuberculosis is related to Mycobacterium tuberculosis but does not cause tuberculosis in either humans or animals.
Section 2: Johne’s Disease
Q1. What is Johne’s Disease?
A1. Johne’s Disease is caused by Mycobacterium avium subspecies paratuberculosis, often known as Map, and is a chronic gastrointestinal infection of adult ruminants characterised by diarrhoea, weight loss, emaciation and eventual death. It is not notifiable in Great Britain although it is in Northern Ireland. It has a worldwide distribution.
Q2. When are animals most likely to become infected?
A2. Under field conditions it is considered that the disease is normally transmitted to animals at an early age, usually under 30 days old, principally by the ingestion of feed or water contaminated by faeces from infected animals. It is believed that some calves may be infected in the womb before they are born, and the bacteria can also be present in the milk of infected cows.
Q3. How common is Johne’s Disease in the UK?
A3. There is limited information on the level of infection in the national herd. Telephone and postal questionnaires were used to survey veterinary practices and dairy farms respectively in the 1990’s. They arrived at estimates of herd prevalence of 1% and 17.5%. The differing estimates underline the limitations of these approaches in accurately measuring prevalence. An abattoir study in the South West of Britain, which identified the presence of Map in mesenteric lymph nodes of cows, resulted in an individual animal prevalence of 3.5%.
A statistically based survey co-ordinated by the Veterinary Laboratories Agency has been commissioned to look at the prevalence of Johne’s Disease in the UK dairy herd. This survey started in October 2006 and will take about 2 years to complete.
Q4. Is Johne’s Disease prevalence increasing in the UK?
A4. Information from the Veterinary Laboratories Agency (VLA) and Scottish Agricultural Colleges (SAC) indicates an increase in diagnoses of Johne’s over the past few years. This suggests that the disease prevalence could be increasing. However, this increase in diagnoses may be due to the overall increase in submissions of samples received for testing for the disease because there is now an increased awareness of the disease in the cattle sector and veterinary profession due to the publication of Defra guidance and industry-led awareness initiatives. Until the prevalence survey has been completed, it is difficult to come to any accurate conclusions about current prevalence or trends.
Q5. What happens when Johne’s Disease is diagnosed in an animal?
A5. There is no statutory action taken, even in Northern Ireland where the disease is notifiable, therefore any action taken is up to the owner. There is no effective treatment for Johne’s Disease. Cattle that exhibit clinical signs are likely to be excreting large numbers of organisms capable of infecting other animals in the herd. Veterinary advice is that they should be removed from the herd and culled.
Q6. What should a farmer do if an animal is thought to be affected with Johne’s Disease?
A6. The farmer should contact his private veterinary surgeon for advice.
Q7. Can cattle be infected with Map without exhibiting symptoms of the disease?
A7. Yes. Cattle are infected early in life but may not develop signs of the disease until they are adults.
Q8. Can infected cattle be detected before they become ill?
A8. Blood tests and tests on faeces are available. Although they can be useful, they are not sensitive enough to detect all infected animals.
Q9. Is a vaccine available to control disease?
A9. The Product License for the live vaccine produced by the Veterinary Laboratory Agency (VLA) expired on the 29th October 2005. However, it is possible to import an inactivated vaccine from Spain by applying for a Special Import Certificate (SIC) from the Veterinary Medicines Directorate (VMD) valid for three months at a time. This does not completely prevent infection but, if linked to management practices to reduce transmission, it may be expected to reduce the amount of disease occurring in infected herds and the level of contamination of the environment with the bacterium. However, the vaccine may interfere with the interpretation of the tuberculin test.
Q10. What else can farmers do?
A10. Farmers should take care that any animals they buy are not carrying the disease. They should ask the vendor for details of the health history of the source herd.
Voluntary control and accreditation schemes are available which register herds believed to be free from the disease. These are run by two private organisations: the Scottish Agricultural College and Herdcare and operate to common standards agreed by an independent industry body known as Cattle Health Certification Standards (CheCS).
Q11. Is Johne’s Disease a problem in other countries?
A11. Johne’s Disease has a worldwide distribution. Sweden and some states in Australia are the only regions that can claim freedom from Johne’s Disease based upon a reliable disease reporting system and extensive surveys.
Q12 Does M. paratuberculosis cause a similar disease in people? I have heard that it can cause Crohn's disease.
A12. There is currently no evidence that M. paratuberculosis causes any similar disease in people who become infected. The Food Standards Agency (FSA) and Department of Health (DH) have kept and continue to keep this matter under close review as the cause(s) of Crohn's disease remains unknown.Q13. Is it safe to drink milk from animals with Johne’s Disease?
A13. A national study on the microbiological quality of cows milk was conducted between March 1999 and August 2000. The results of the survey, which found Map in approximately 2% of pasteurised milk on retail sale, were reported to the Advisory Committee on the Microbiological Safety of Food (ACMSF) in September 2000. The Committee noted that the risk to human health was neither proven nor disproved and did not recommend any change in the current advice regarding the consumption of milk, i.e. on the basis of current evidence there is no need for anyone to change their dietary habits.
A Drinking Water Inspectorate studying in 2005 found no association between consumption of milk and dairy products and a higher risk of developing Crohn’s Disease. The full report can be viewed at www.dwi.gov.uk.
Q14. Is it safe to eat meat from animals with Johne’s Disease?
A14. No reliable reports have linked consumption of meat from animals with Johne’s Disease to Crohn’s Disease. The Food Standards Agency (FSA) and Department of Health have kept and continue to keep this matter under close review with their expert committees. There is no epidemiological or microbiological evidence to suggest that consumption of meat from animals with Johne’s Disease has caused Crohn’s Disease. A Republic of Ireland survey of 113 minced beef samples collected from a single meat processing plant over a 4 month period found no viable Map. (Reported by Dr Irene Grant, QUB, at a Campden and Chorleywood Food Research Association Conference in June 2005.) The risk to human health is neither proven nor disproved and the FSA do not recommend any change in the current advice regarding the consumption of meat, i.e. on the basis of current evidence there is no need for anyone to change their dietary habits.
A recent Drinking Water Inspectorate study found a statistical association between the consumption of meat and Crohn’s Disease. The study was not specifically designed to investigate meat therefore caution in the interpretation of the findings is required. The full report can be viewed at www.dwi.gov.uk. The Advisory Committee on the Microbiological Safety of Food (ACMSF) considered the DWI report in September 2005 and concluded that the results did not point to a causal role for Map in Crohn’s disease and did not suggest a need to change current FSA advice on consumption of meat.
Q15. What action did the EU Scientific Committee on Animal Health and Animal Welfare (SCAHAW) recommend regarding animals infected with Map?
A15. SCAHAW stated “aside from any possible link with Crohn’s Disease, the development of the necessary tools to eradicate “paratuberculosis” from animals should also be a priority” and highlighted the need to:
- develop improved diagnostic methods
- develop improved vaccines
- obtain the complete genomic sequence of Map
- determine the distribution and levels of Map in infected animals
- experiment with time/temperature combinations of pasteurisation to see which would inactivate Map
- determine the survival of Map in the environment and the role of natural water and water supplies in transmission of Map
- carry out statistically robust studies on prevalence of Map in domestic and wild animals (both to assist future eradication programmes and to compare with incidence of Crohn’s Disease)
Q16. What work is Defra undertaking on the Map strategy?
A16. A statistically based survey has been commissioned to look at the prevalence of Johne’s disease in the UK dairy herd. This study is a collaboration between the Veterinary Laboratories Agency (VLA), the Scottish Agricultural College (SAC), Moredun Research Institute and the Agri-Food and Biosciences Institute (AFBI) and is funded by Defra, the Scottish Executive, Welsh Assembly Government and the Department of Agriculture and Rural Development in Northern Ireland (DARD).
The aims and objectives of the study are to:
1. determine herd level prevalence of this disease in the national dairy herd in a statistically robust manner;
2. determine the effect of management practices and herd location on disease prevalence;
3. establish the genetic diversity of Map (the bacteria which causes the disease)in the UK to help understand it’s spread and provide a baseline for comparison with human isolates;
4. assess methodologies for future on-going monitoring of the disease.
The study began in October 2006 and will take about 2 years to complete. The full report documenting findings of the study will be made public at the end of 2008.
Q17. What guidance has been given to the cattle industry?
A17. Defra and devolved administrations launched guidance on the control of Johne’s Disease in dairy herds at the Dairy Event in September 2004. Two documents were published:
- A 10 point plan, in the form of a glossy A5 leaflet giving advice about on-farm priorities, for general distribution to all dairy farmers;
- More detailed Guidance Notes explaining the background to the advice, to be used as a basis for discussion between veterinary surgeons and dairy farmers in setting up plans for monitoring and control.
Both documents are also available on Defra’s and DARD’s websites. The Guidance Notes were distributed to all milk producers, large animal Local Veterinary Inspectors (LVIs), Animal Health Offices, Regional Veterinary Laboratories, Scottish Agricultural Laboratories and libraries at Veterinary and Agricultural Universities.
Defra has also worked with a partnership led by the National Beef Association to raise awareness of Johne’s disease in the beef sector. Guidance to the veterinary profession was published in 2006 which will be the start of an industry campaign to reduce the prevalence of Johne’s disease in the GB beef herd.
Q18. What research is Defra currently undertaking on Map?
A18. . Defra funded a major review of Johne’s Disease by the Scottish Agriculture College (SAC) “Assessment of Surveillance and Control of Johne’s Disease in farm animals in GB”. The report included an economic analysis and recommendations for enhanced surveillance and control of the disease as well as future research requirements. This was used as a basis for developing revised guidance for the cattle industry on the prevention and control of Johne’s Disease.
The need for further research on this disease needs to be balanced against demands for research funding and these needs have to be prioritised. In view of the absence of an established link between Johne’s Disease in cattle and Crohn’s Disease in humans, research on Johne’s Disease was considered alongside the need for research on other non-zoonotic endemic livestock diseases. It is important that before considering what further research is required, we have a better understanding of how many herds are likely to be affected by Johne’s Disease in the UK. The findings of the prevalence survey that is currently underway will be used to inform future policy decisions and highlight any future research needed.
Some research has been maintained in Scotland by the Scottish Executive. Defra has a large research programme on bovine tuberculosis caused by the related organism Mycobacterium bovis. Some of the outputs from this research will also assist in filling some gaps in knowledge on Map.
Q19. Why was vaccination not considered to offer wider benefits in controlling Johne's Disease in the Scottish Agricultural College’s Report?
A19. Although vaccination has been shown to reduce the number of clinical cases in an infected cattle herd, it does not eliminate infection or the number of animals that excrete Map, nor prevent the spread to other herds. Furthermore, vaccination interferes with some diagnostic tests and so may hamper surveillance and make it difficult to demonstrate herd freedom from infection.
Section 3: Crohn’s Disease
Q1. What is Crohn’s Disease?
A1. Crohn’s Disease is a long-term illness in people that causes inflammation in the gut. It can affect any part of the digestive system from the mouth to the terminal rectum. The parts most often affected are the ileum (last part of the small intestine) and the colon. The symptoms include abdominal pain, fever and weight loss.
Q2. Why has M. paratuberculosis been linked to Crohn’s Disease in humans?
A2. It has been proposed that that M. paratuberculosis has a role to play in Crohn’s disease because Johne’s disease in cattle presents a similar clinical picture and the organism has been isolated from the intestines of some patients with Crohn’s disease.
Q3. How strong is the evidence of a link between M. paratuberculosis and Crohn’s Disease?
A3. Experts worldwide differ in their opinion on whether M. avium subspecies paratuberculosis causes Crohn’s disease or some cases of Crohn’s disease. The Advisory Committee on Dangerous Pathogens and the Chief Medical Officer's National Expert Panel on New and Emerging Infections have both concluded that there is no evidence of a causal a link between M. paratuberculosis infection and development of Crohn's disease. A similar view was reached by the EU Scientific Committee on Animal Health and Animal Welfare. The Food Standards Agency (FSA) and Department of Health have kept and continue to keep this matter under close review as the cause of Crohn's disease is not yet known.
Q4. Is M. paratuberculosis present in pasteurised milk?
A4. The FSA funded a national survey of milk to find out whether Map is present in heat-treated milk. The results of the FSA commissioned survey found Map in approximately 2% of pasteurised milk on retail sale.
Q5. Is it safe to drink milk from animals with Johne’s Disease?
A5. A national study on the microbiological quality of cow’s milk was conducted between March 1999 and August 2000. The results of the survey, which found Map in approximately 2% of pasteurised milk on retail sale, were reported to the Advisory Committee on the Microbiological Safety of Food (ACMSF) in September 2000. The Committee noted that the risk to human health was neither proven nor disproved and did not recommend any change in the current advice regarding the consumption of milk, i.e. on the basis of current evidence there is no need for anyone to change their dietary habits.
A Drinking Water Inspectorate study in 2005 found no association between consumption of milk and dairy products and a higher risk of developing Crohn’s Disease. The full report can be viewed at www.dwi.gov.uk.
Q6. Is it safe to eat meat from animals with Johne’s Disease?
A6. No reports have linked consumption of meat from animals with Johne’s Disease to Crohn’s Disease. The FSA and Department of Health have kept and continue to keep this matter under close review with their expert committees. There is no epidemiological or microbiological evidence to suggest that consumption of meat from animals with Johne’s Disease has caused Crohn’s Disease. A Republic of Ireland survey of 113 minced beef samples collected from a single meat processing plant over a 4 month period found no viable Map. (Reported by Dr Irene Grant, QUB, at a Campden and Chorleywood Food Research Association Conference in June 2005). The risk to human health is neither proven nor disproved and the FSA do not recommend any change in the current advice regarding the consumption of meat, i.e. on the basis of current evidence there is no need for anyone to change their dietary habits.
A recent Drinking Water Inspectorate study found a statistical association between the consumption of meat and Crohn’s Disease. The study was not specifically designed to investigate meat therefore caution in the interpretation of the findings is required. The full report can be viewed at www.dwi.gov.uk. The Advisory Committee on the Microbiological Safety of Food (ACMSF) considered the DWI report in September 2005 and concluded that the results did not point to a causal role for Map in Crohn’s disease and did not suggest a need to change current FSA advice on consumption of meat.
Q7. Is M. paratuberculosis present in drinking water?
A7. A study of Map in distribution systems and consumers' premises completed by the Public Health Laboratory Service (PHLS), now part of the Health Protection Agency (HPA), in August 2003 did not detect the presence of Map. This strengthens the view that drinking water is unlikely to be a source of exposure.
Q8. Is it safe to consume drinking water or milk and dairy products potentially contaminated with Map?
A8. A recent Drinking Water Inspectorate study found that neither drinking water potentially contaminated with Map or the intake of milk and dairy products are associated with a higher risk of developing Crohn’s Disease. The full report can be viewed at www.dwi.gov.uk.
Section 4: Future Policy
Q1. What is the Government’s future policy on issues of protecting human health from Mycobacterium avium subspecies paratuberculosis in pasteurised milk?
A1. Since small numbers of Map organisms have been shown to survive milk pasteurisation, the Food Standards Agency has developed, in consultation with all relevant stakeholders, a precautionary strategy to reduce human exposure to Map via the milk supply. This focuses on a combination of initiatives in the milk production and processing chain because a single measure that could be quickly applied to control Map in milk has not been identified. Responsibility for delivery of the Strategy rests jointly with Defra and the FSA.
Surveillance, Zoonoses, Epidemiology and Risk
(last updated 19 November 2007)
Page last modified:
22 November 2007