CHICAGO (Reuters) - Eighteen pork plant workers in Minnesota, at least five in Indiana and one in Nebraska have come down with a mysterious neurological condition they appear to have contracted while removing brains from slaughtered pigs, U.S. researchers and health officials said on Wednesday.

They said the illness is a new disorder that causes a range of symptoms, from inflammation of the spinal cord to mild weakness, fatigue, numbness and tingling in the arms and legs.

“As far as we are aware it is a brand new disorder,” said Dr. Daniel Lachance of the Mayo Clinic in Rochester, Minnesota, who presented his findings at the American Academy of Neurology meeting in Chicago.

Lachance has been following the 18 Minnesota patients, all of whom have evidence of nerve involvement, typically affecting the legs.

He said tests showed patients had damage to the nerves at the root level near the spinal cord, and at the far reaches of their motor nerves, where the nerves connect with muscle.

The first cases of the condition were reported in November of last year at Quality Pork Processors Inc in Austin, Minnesota, where workers had been using compressed air to blow pork brains out of the skull cavity.

Lachance said this process appears to be triggering some sort of inflammatory response. So far, no infectious agent has been found that could explain the illness.

‘STRONG ASSOCIATION’

Lachance said it is possible that bits of pig brain stimulated an immune response in the bodies of the workers, causing their immune systems to improperly attack their own nerve tissue.

“It is a very strong association -- the fact that we are talking about harvesting (pig brains) and potentially exposing workers to nervous system tissue and then they are coming down with a neurological syndrome,” he said in a telephone interview.

Dr. James Sejvar of the U.S. Centers for Disease Control and Prevention in Atlanta said it is unlikely the condition could be passed from person to person.

“It doesn’t appear this is in any way a foodborne illness,” Sejvar told a media briefing. He said the processing technique used appears to be very uncommon.

“We canvassed 25 of the largest pork processors in the United States,” Sejvar said. “We have identified only these three plants that use this process.”

All three plants have suspended the processing practice as a precaution.

While symptoms range in severity, most of the cases are mild. “Most of these patients have relatively mild weakness on their examinations or in fact no weakness, but have a predominance of sensory symptoms. They could be walking around and not have the appearance of being ill,” Lachance said.

He said those who were mildly affected received drugs that address numbness and pain, and those who were more severely affected were treated with drugs that suppress or modulate the immune system.

“No one has completely recovered,” Lachance said, adding, “Most have improved to a very modest degree, mainly in terms of their fatigue and sensory symptoms.”