CHICAGO It started with tingling in the fingers and toes, followed by weakness in the legs.
"It wasn't a normal neurologic illness," said Dr. Aaron DeVries, an epidemiologist with the Minnesota Department of Health who helped lead the state's investigation of a mysterious condition that sickened 18 workers at a Southern Minnesota pork processing plant.
Now, more than a year after their symptoms started, the workers are responding to treatment for the nerve illness that is teaching doctors new lessons about autoimmune disease.
DeVries got involved after a cluster of workers at Quality Pork Producers Inc in Austin, Minnesota, became too weak to visit the fourth-floor health clinic, leading the plant's nurse to alert health authorities.
"The most common denominator was people saying, 'We can't make it up the stairs,'" he said.
Most had been assigned to the head table, where they used compressed air to blow the brains out of pig skulls.
"We observed how brain material was both splattered around on other machines and other workers close by," DeVries said. "But there was also smaller material that remained in the air."
It turns out that all of the sickened workers had been exposed in some way to a fine mist of pig brain matter that triggered a new type of autoimmune disease.
In the 15 months since their illness was first reported, all have responded to immune therapy but they continue to have symptoms and many have mild pain.
'EXPERIMENT OF NATURE'
"This whole thing was a man-made experiment of nature," said Dr. Daniel Lachance of the Mayo Clinic in Rochester, Minnesota, who will present his latest findings on the pork workers' disease at a neurology meeting next month.
"It presents an opportunity to understand a phenomenon that is potentially important to all of us -- autoimmune disease," Lachance said in a telephone interview.
Lachance and Dr. James Dyck of Mayo worked closely with health department doctors to learn as much as possible about what made the workers sick.
While they now believe it was an autoimmune response, it took scores of interviews with plant workers, numerous tests and months of observations to make that call.
They considered infectious agents such as prions -- proteins known to wreak havoc on the brain in diseases such as mad cow and Creutzfeldt-Jakob disease.
But the symptoms did not fit. "Prion illnesses are almost uniformly progressive. People get sicker and sicker until they die from it," DeVries said.
Although they are still doing tests, they believe the workers developed antibodies to proteins from the pig brain tissue. Testing shows all have a unique antibody not seen before.
"What happens is our body makes a specific antibody and the antibody is targeting this foreign protein," DeVries said.
"By accident, it also attaches to a protein within our own body. This is, in a certain sense, collateral damage."
The researchers hope further studies on this disease will aid understanding of other autoimmune disorders, where the trigger is not known. "Even though this is an isolated incident, it is certainly going to open up doors in neurology research," DeVries said.
(Editing by Maggie Fox and Eric Walsh)