'Pig Brain Mist' Disease Mystery Concludes

More than a year after developing a mysterious neurological disorder eventually linked to their inhalation of aerosolized pig brains, 24 pork plant workers have regained their health.

Their recovery, described Tuesday in a presentation scheduled for the American Academy of Neurology's annual conference, ends a story that began in November 2006, when three workers at a Quality Pork Processors plant in Austin, Minnesota reported strange and similar symptoms: fatigue, numb and tingling legs, pain, difficulty walking.

Doctors didn't know what caused the problem, but tests found severe spinal cord inflammation, suggesting an autoimmune disorder: the patients' immune systems no longer recognize their bodies' nerves, and attacked them.

Over the following months, the number of cases rose to 24, and past cases of a similar condition were uncovered at a meat processing plant in Indiana. Doctors scrambled to find a common clue. Both plants were among a total of three in the country to process pig brains for consumption -- and each of the 24 workers at the Minnesota plant worked in the "head table" room.

At the head table, pig heads were cut open and the brains forced out with a burst of compressed air. In the process -- a process that took place about 1,400 times an hour -- some of the brains were blown into a fine mist. Not everyone in the room got stick, but the closer people stood to the table, the more likely they were to be afflicted.

"When you're breathing in pig brain tissue, your body develops an antibody against it," said Mayo Clinic neurologist James Dyck, who helped treat the workers. Antibodies are chemicals used by the immune system to tag foreign bacteria and substances. "There's enough overlap between pig brains and human brains that it was a problem."

The workers' immune systems mistakenly targeted their own nerves. Fortunately, most responded to treatment with immunotherapy and steroids, and six improved without any treatment at all. None of the workers, however, have recovered fully.

Exactly why the rash of cases emerged so suddenly isn't known. The factory shut down the pig brain processing center soon after the disease emerged, and no new cases have been reported.

According to Dyck, the near-tragedy has a silver lining: doctors had a chance to study the emergence of autoimmunity -- a phenomena underlying dozens of diseases, many of which are barely understood and difficult to treat -- in a manner impossible inside a laboratory.

"This is an experiment that occurred by accident," he said. "What is an immunodeficiency? How does that autoimmune process happen? What's getting attacked?" he said. "This is teaching us about how the body and the immune system works."