Chamberlin was an associate professor of gastroenterology at Texas Tech University before moving to Billings, Mont., to treat patients at St. Vincent Hospital.

He likens the MAP controversy to the one that ensued over the link between H. pylori and stomach ulcers 30 years ago. Doctors entrenched in the belief that stress and spicy foods caused ulcers resisted an Australian physician’s evidence that the real culprit was a bacterial infection.

Desperate to prove his point, the physician drank a test tube of the bacteria and swiftly developed an ulcer. Then, instead of using the customary antacids to treat it, he took antibiotics – today considered the standard treatment for most stomach ulcers.

Gulping down a vial of MAP might not lead to disease. But if it did, Crohn’s symptoms are more serious and chronic than stomach ulcers, said Chamberlin.

"Believe me, no one wants to get Crohn’s disease,” said Chamberlin, whose center-stage treatment for the ailment is a cocktail of antibiotics. Properly selected antibiotics are reducing symptoms in many of his patients, he said.

"Philosophers like to say that we never know anything for certain and that truth is based on probabilities,” he said. "That said, with the amount of evidence that has accrued, the probability of MAP being one of the agents that causes Crohn’s symptoms meets my threshold.”

New vaccine to protect

And so, as science moves in fits and starts and skepticism continues to percolate, Davis will soon enter his third decade of MAP research on cattle. In the meantime, seemingly healthy cows continue to transmit the germ into the human food chain.

If scientists can’t reach a consensus on whether this is safe or harmful, Davis hopes to plow ahead by studying the effectiveness of the vaccine that he and a group of international scientists developed by altering MAP’s DNA. Preliminary tests, published in 2011, show that it keeps MAP from launching the biological chaos of infection inside the intestines of cattle and goats, he said.

If scientific scrutiny shows that the vaccine works and it is then administered to cattle, will fewer people get struck by that painful, incurable disease we call Crohn’s?

"I’m not an alarmist; I’m a realist,” said Davis. "That would be the moment of truth.”