The head of Mayo Clinic's Peripheral Nerve Section is Doctor P. James B. Dyck. He has been seeing workers from the Quality Pork Processing plant who have symptoms of a neurological illness.

Dyck says doctors aren't drawing any conclusions yet, but it's possible that contact with neural material could have led to an autoimmune response. That's when the body's immune system attacks itself.

"I think that's a very intriguing idea," he says. "That neural tissue could have perhaps set up some sort of immune response causing this type of neuritis."

Neuritis is the inflammation of the peripheral nervous system. That system controls much of voluntary and involuntary movement, like picking up a pencil or dilating pupils.

Dyck says researchers have been able to induce an allergic neuritis which eventually led to a nervous system disease. But Dyck says at this point there is no established link between contact with pig brains and an auto-immune response. Another potential cause could be a virus.

Dyck says two more workers are about to be tested at the Mayo Clinic. About half of the 11 workers who have already been tested showed signs of the disease Chronic Inflammatory Demyelinating Polyneuropathy (C.I.D.P.). The disease slowly weakens muscles and causes numbness.

However, after examining the workers, Dyck says it's unlikely these workers actually have the disease.

"These patients don't tend to have all the same symptoms and findings," he says. "There are some similarities on some testing, but there are also major differences."

Dyck says the difference is important because C.I.D.P. is a chronic disease. He says so far all they know is that this group of people have inflammatory nervous system diseases.

Mayo Clinic neurologist Doctor Daniel Lachance says it's too early to say whether these patients will recover.

"I can say that I've had one patient who I've followed without treatment who has improved enough to return to the same workplace, not to the same job. I made sure of that," he says.

Minnesota State Epidemiologist Ruth Lynfield says state health department officials are interviewing between 80 and 100 workers at Quality Pork Processing. Those include all of the people who worked at the table where pig heads were processed and a random sample of people from the production floor.