A needling question: Does Pasteurization really kill M. paratuberculosis?

Some scientists question USDA, FDA announcements that it does


Several researchers are criticizing a USDA study that supposedly shows pasteurization kills the organism causing Johne's disease.

The scientists wonder why government agencies embraced the study, even though other several other studies show the organism survives pasteurization. They also question the limited scope and research methods of the USDA study.

The study has been widely cited in the agricultural press and by other government agencies.

In a response to a request from the U.S. Animal Health Association, the Food and Drug Administration said "the latest research shows conclusively that commercial pasteurization does indeed eliminate this hazard" (the presence of Mycobacterium paratuberculosis).

"The FDA response reads more like a political response than a scientific assessment," says Michael Collins, a microbiologist and veterinarian with the University of Wisconsin School of Veterinary Medicine. "I don't see how they can say that, unless they were selectively reading the literature.

Collins recently reported pasteurization didn't kill certain concentrations of the organism. Such "surges" in M. paratuberculosis concentration could occur in commercial production depending on the handling and mixing of contaminated milk.

Rod Chiodini, a microbiologist associated with the Rhode Island Hospital at Brown University started studying the organism in the 1980's and was the first to demonstrate that the organism survived pasteurization. He says the USDA study was too small and limited to provide enough conclusive data.

Moreover, Chiodini says the organism may have been cultured in a manner that weakened it and that samples used to inoculate milk may have been taken at a stage when the organism was already dying.

Other researchers say the samples weren't cultured long enough to really determine whether any of the organisms survived pasteurization and questioned whether the organism was weakened by pre-pasteurization procedures such as freezing and sonication.

The government's stance has alarmed some of those suffering from Crohn's disease, a severe inflammatory enteritis that has been linked with M. paratuberculosis. Many Crohn's patients have requested research to determine whether the organism is found in dairy products and beef.

"It appears they (the USDA) designed a study to make sure that no paratuberculosis bacteria would survive pasteurization, or be detected if they did" says Alan Kennedy, who has Crohn's disease and closely monitors research concerning the links between Johne's disease and Crohn's disease.

According to Kennedy, two experts on M. paratuberculosis submitted a proposal to the USDA in 1991, 1992 and 1993 to determine whether the organism was found in retail dairy products. Although reviewers considered the study sound and important the USDA refused funding, in part because the proposed research team did not include a food microbiologist (The study conducted by USDA did not include a food microbiologist.)

"If M. paratuberculosis is the cause of Crohn's disease, then it is likely that contaminated dairy and beef products are responsible for destroying the health of the 20,000 Americans who develop Crohn's disease each year. Most of them will be 15 to 29 years old," Kennedy says.

The study rejected by the USDA was proposed by Chiodini and Dr John Hermon-Taylor, chairman of the department of surgery, St. Georges Hospital Medical School, London, England, and an internationally known expert on Crohn's disease and on the genetics of M. paratuberculosis. Two months after the USDA submitted its pasteurization study, Dr. Hermon-Taylor detected the organism in retail pasteurized milk in England.

To date, no study has determined whether live M paratuberculosis is found in retail meat and milk in the U.S.

Collins says farmers understand evidence showing the possibility that M. paratuberculosis may enter the food supply and want to do whatever is necessary to prevent this. "It is not in the best interests of the dairy industry for leaders to appear as though they are concealing the truth. We all depend on a healthy dairy industry, and issues such as this should be discussed openly and honestly." says Collins.

Joseph Smucker, team leader of FDA's Milk Safety Team, said he did "not have the expertise nor the clearance from the FDA to speak to you on this subject." Calls to the FDA's press office were returned only after we contacted John Adams, director of milk safety and animal health for the National Milk Producers Federation.

Stephanie Bernier, a spokesperson for the FDA, says it is 'very unusual' for an official of the FDA not to respond directly to press inquiries, and sent a copy of the USDA study. No FDA official concerned with milk safety responded to inquiries.

Adams praises the scope and scientific integrity of the USDA study, noting that it simulated the high-temperature, short-time (HTST) pasteurization widely used in the U.S. "HTST pasteurization is well-controlled and allows very little opportunity for particles of milk not to reach the desired temperature and time of pasteurization." He says much of the research conducted in other countries has utilized "test-tube" pasteurization systems that are not as carefully controlled as HTST pasteurization.

"Of course, the USDA research needs to be reproduced elsewhere, but it was good science," Adams says.

Wisconsin Agriculturist
July 1998