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Involvement of the pathogen of bovine paratuberculosis unlikely in the triggering of Crohn's disease but cannot be ruled out

30/2001, 21.09.2001

Experts discuss in BgVV possible links, opportunities for intervention and the need for research

The question about the causal relationship between bovine paratuberculosis (Johne's disease) and Crohn's disease in humans was the focus of an expert panel in Berlin to which the BgVV had invited human and veterinary doctors from federal institutes, federal research bodies, universities and official food control bodies on 19 September 2001. The experts thought that a causal relationship was rather unlikely. But they did think it is conceivable that the pathogen of Johne's disease, M. paratuberculosis, could aggravate the clinical picture of Crohn's disease and possibly be a trigger in some patients. The experts agreed that the data available did not suffice for a definitive health risk assessment.

Crohn's disease in humans involves chronic non-specific inflammation of the intestines which can affect all sections of the digestive tract. A series of factors may trigger the disease including genetic, immunological, diet and psychosocial ones. The involvement of various types of bacteria including M. paratuberculosis is discussed. Three to six out of 100,000 people develop this intestinal infection in Germany every year. The figure has remained relatively constant over the last few years.

Johne's disease in cattle is also a chronic intestinal disorder. It is incurable and the symptoms are persistent diarrhoea and progressive emaciation of the animals. Calves become affected through the milk of sick mother animals or take in the mycobacteria through feed and water which is contaminated with pathogen-containing faeces. The disease occurs around the world and is also widespread in German cattle stocks. National figures about the actual degree of stock contamination are not available for Germany. There are no representative studies either because reliable early diagnosis was not possible up to now. The experts point out that M. paratuberculosis is increasingly becoming a problem of animal health and, by extension, an economic problem. The fact that the pathogen was detected in some patients (but also in some healthy individuals) and that successful treatments with antimycobacterial medicines have been reported would seem to point to a possible involvement of M. paratuberculosis in the triggering or development of Crohn's disease. Overall, however, the research results are contradictory.

So far the question about the exposure of humans to the pathogen is largely unanswered. Milk and dairy products may be contaminated and, under some circumstances, also vegetables which have grown on fields with "natural fertiliser" . In the United Kingdom the mycobacterium paratuberculosis was found in pasteurised milk on the market. Scientists from the Federal Institute for Milk Research in Kiel point out that the customary pasteurisation of milk in Germany considerably reduces the germ count of M. paratuberculosis but that heating does not suffice in order to completely kill the germs. So far it was not possible to establish on what scale milk and dairy products in Germany actually contain the M. paratuberculosis.

Before a definitive assessment of the health relevance of M. paratuberculosis for humans, particularly with regard to a possible involvement in Crohn's disease, is possible, a series of open questions must be answered:

• Is an infection with M. paratuberculosis involved in the case of Crohn's disease?
• Are the strains of pathogen found in animals suffering from paratuberculosis identical with those detected in patients suffering from Crohn's disease?
• Are antimycobacterial medicines effective in the treatment of Crohn's disease or is the efficacy observed in some combination products used up to now merely based on their general antibacterial effect?
• How high is the degree of contamination of German cattle stocks also in respect of possible regional differences?
• How high is the degree of contamination of milk and dairy foods and could the use of other technologies render food safer with regard to the incidence of M. paratuberculosis?

In order to answer these questions the experts recommend the following studies:

• Incidence of M. paratuberculosis in patients suffering from Crohn's disease and possible involvement in the course of the disease.
• Regional comparison of the incidence of paratuberculosis in cattle stocks with cases of Crohn's disease in humans.
• Comparison of the M. Paratuberculosis strains isolated from animals and humans for strain identity.
• Defined infection experiments in animals with strains isolated from patients suffering from Crohn's disease.
• National monitoring of tank milk samples following successful validation of a serological test to identify contaminated dairy herds.
• Investigation of foods for the incidence of M. paratuberculosis.
• Examination of the use of food technology methods to eliminate M. paratuberculosis.

The participants in the expert panel came out in favour of close links between the competence network Crohn's disease and the network for foodborne infectious diseases which is co-ordinated at the Robert Koch Institute. All available studies which have examined a possible link between bovine paratuberculosis and Crohn's disease in humans should be reassessed. A control study involving the use of antimycobacterial medicines is to begin shortly. The expert group does not expect results from the above-mentioned studies for two years because of the comprehensive study design and the lengthy detection process for the pathogen. The need for specific consumption recommendations is not considered necessary at the present time from the human medical angle.

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