Milk May Be the Carrier of Crohn’s
If, as some scientists are now convinced, Crohn’s disease is caused by a microorganism, the question becomes: How is it transmitted?
The shocking answer, they say, is through that most sacrosanct of beverages--milk. The microorganism under suspicion, Mycobacterium avium subspecies paratuberculosis, or MAP, is common in U.S. dairy herds, activists argue, and it is not killed by conventional pasteurization.
Transmission of MAP from infected cattle to humans through milk could explain much about the occurrence of Crohn’s, including its geographical distribution and rising incidence.
The purported spread of MAP through milk “constitutes a public health disaster of tragic proportions,” said Dr. John Hermon-Taylor of St. George’s Hospital Medical Center in London.
Both the U.S. dairy industry and the Food and Drug Administration argue vehemently that the U.S. milk supply is safe and that pasteurization is effective at removing any potential threats.
But several large milk distributors in Britain have already changed their pasteurization procedures to make it more likely that the microorganism will be killed. The suspected links between MAP, milk and Crohn’s have received a great deal of attention in that country, but none in the United States.
Some facts seem indisputable. MAP causes Johne’s disease in cattle, a debilitating disorder whose symptoms are identical to those of Crohn’s in humans. Large numbers of cattle in the United States are infected by the organism.
According to a National Animal Health Monitoring System study conducted in 1996, 22% of U.S. dairy herds have infected cows. The cows secrete the mycobacterium in their milk.
And there the two sides part company. The dairy industry argues that the link between MAP and Crohn’s is unproved and that, even if there were a link, pasteurization kills the microorganism.
“It is the position of the Food and Drug Administration that the latest research shows conclusively that commerical pasteurization does indeed eliminate this hazard,” Joseph Smucker, FDA’s milk safety team leader, wrote to activists concerned about the risk.
But the activists have compiled a growing dossier of evidence. Dr. Walter Thayer of Rhode Island Hospital notes that Crohn’s is not distributed evenly around the world, but is seen only in milk-drinking areas--Australia, southern Africa, Europe, the United States, Canada and New Zealand. It is rare in India, where they drink milk but boil it first.
Work by Hermon-Taylor and Dr. Irene Grant of Queen’s University in Belfast, Ireland, has shown that DNA from MAP was present in about 20% of milk samples collected throughout the country. Living bacteria could be grown from many of the samples.
An as-yet-unpublished study by the Ministry of Agriculture in Britain found that researchers could grow MAP from at least 3% of samples of commercial pasteurized milk, Hermon-Taylor said. “It confirms, as sure as God made little green apples, that retail milk in Britain is a definite source of human exposure to these bugs,” he added.
MAP is extremely difficult to kill, and commercial pasteurization--which involves heating milk to 161 degrees Fahrenheit for 15 seconds--is not sufficient, according to studies by Grant. Heating to higher temperatures--up to 194 degrees for the same period of time--is also not effective, she said, but increasing the pasteurization time to 25 seconds, even at 161 degrees, is.
Last year, several large milk distributors in Britain told their suppliers to increase pasteurization time, and that has been accomplished. Activists want to see the same steps taken here.
“There comes a point in time where consumer health takes precedence over commerical concerns,” says Karen Meyer, president of the Paratuberculosis Awareness and Research Assn. “If a human pathogen is entering the food chain, that is a major concern. We need to ensure the protection of the public health.”
