We know that pork is not very healthy, but pig brain proves harmful in a very unexpected way. 18 pork plant workers in Minnesota, 5 in Indiana and 1 in Nebraska have been detected so far with a mysterious neurological disease got while removing brains from slaughtered pigs, as signaled at the American Academy of Neurology meeting in Chicago. The condition appears to be totally new, provoking 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. 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," said Dr Daniel Lachance of the Mayo Clinic in Rochester, Minnesota, who has been taking care of the 18 Minnesota patients.

The first case was reported in November of 2007 at Quality Pork Processors Inc in Minnesota, and the researchers believe the disease has a connection with the method of using compressed air to blow pork brains out of the skull.

"This process appears to be triggering some sort of inflammatory response," said Lachance.

So far, the researchers have not detected an infectious agent associated with the condition.

"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," said Lachance.

"It is unlikely the condition could be passed from person to person. It doesn't appear this is in any way a food-borne illness. The processing technique used appears to be very uncommon. We canvassed 25 of the largest pork processors in the United States. We have identified only these three plants that use this process," said Dr James Sejvar of the US Centers for Disease Control and Prevention in Atlanta.

The practice was suspended in all the processing plants.

"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. 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. Most have improved to a very modest degree, mainly in terms of their fatigue and sensory symptoms," said Lachance.