Pressure is mounting on the Department of Agriculture to screen all imported cattle for Johne's disease because of emerging evidence that it may be linked to Crohn's disease in humans.
The most recent call for such screening has come from the Food Safety Authority of Ireland Consultative Council, The Irish Times has learned. It has advised that Ireland should not wait for evidence of a direct link between the two diseases to emerge before taking action. The committee has argued that the department should apply the precautionary principle to the protection of consumers' health and it would also make sense from an animal health point of view also.
The pathology of Johne's disease superficially resembles that of Crohn's disease in humans andsome researchers have shown evidence of Johne's disease in the intestinal tissues of Crohn's disease patients.
Crohn's disease is a debilitating inflammatory bowel disease in humans and proposed causes include bacterial or viral infection, diet or exposure to tobacco smoke, genetic abnormality and immune dysfunction. Cases of the disease have been increasing with the developed world.
Mycobacterium avium subsp. paratuberculosis (known as MAP) is an organism which can cause chronic inflammation of the intestine (Johne's disease) in cattle, sheep and goats as well as in other animals including rabbits. Some researchers have shown evidence of MAP in the intestinal tissues of Crohn's disease patients.
However, the exact role, if any, of MAP in the aetiology of Crohn's disease has not been fully established. Exposure to high levels of the MAP organism can arise from direct contact with infected farm animals or by drinking raw milk from infected animals. Exposure to lower levels of the organism could possibly arise from heat-treated milk or from consuming contaminated water. MAP can survive for prolonged periods of up to nine months on contaminated pastures and in the environment.
A recent survey of UK milk undertaken at Queen's University, Belfast, identified MAP in both unpasteurised and pasteurised milk. After discussions with the Food Safety Authority of Ireland (FSAI), as a precautionary measure, Irish manufacturers have raised milk pasteurisation times and temperatures to greater than or equal to 72 degrees for 25 seconds, as recommended by the EU Scientific Committee.
Johne's disease is prevalent in the national herds of several EU member-states but it has been rare in Ireland, where it has been a notifiable disease since 1955. Pre-1992 import controls required animals to be tested and quarantined. However since the single market was introduced there has been importation without a requirement to screen for the disease.
Increasing numbers of cases have been imported into Ireland in the last decade, with the large numbers of high-yielding dairy cows and continental breeds imported by Irish farmers. Many of the animals come from the Netherlands to replace herds hit by BSE and there is a 20-40 per cent infection of herds there.
All the imported cattle are identified on computer and it would be possible to identify the herd with imports and target them for MAP testing.
The EU Scientific Committee on Animal Health and Animal Welfare, the Microbiology Sub-Committee of the FSAI, the Advisory Committee on the Microbiological Safety of Food of the UK Food Standards Agency and other expert groups have concluded there is insufficient evidence at present to establish a link.