The Centers for Disease Control and Prevention (CDC) is asking neurologists to report cases of neuropathy among patients who have been exposed to pig butchering or processing during the past year.
The announcement follows reports of people who developed symptoms of inflammatory neuropathy while working at a pork processing plant in Minnesota. The CDC has called the cluster of cases “unusual.”
This past November, the Minnesota Department of Health launched an investigation into the cases at Quality Pork Processors plant in Austin. Since all 12 people who have shown symptoms of the illness worked in an area where compressed air was used to extract pig brains, officials believe the illness may have been caused by exposure to an agent in airborne brain particulate matter. The cases occurred between November 2006 and November 2007. (See “Alert to Neurologists — Help Needed to Help Solve Mysterious Neurological Illness at Minnesota Pork Plant,” Neurology Today, Feb. 7, 2008, p. 3)
The employees of a pork plant in Indiana who used a compressed air device to extract pig brains may have developed a similar illness, said Ermias Belay, MD, a medical epidemiologist in the Division of Viral and Rickettsial Diseases at the CDC's National Center for Zoonotic, Vectro-borne, and Enteric Diseases. The agency is currently assisting the Indiana State Department of Health in investigating the illness in these patients, he added.
Elizabeth Hart, a spokeswoman for the Indiana health department, refused to name the plant in Indiana but said the CDC informed the department about two cases in early January. The CDC's Dr. Belay said there may now be several more reports of the illness; he did not specify how many. The federal agency had determined that three pork-processing plants in the US — one each in Minnesota, Indiana, and Nebraska — use the brain cleansing method. At press time, however, no cases had been reported in Nebraska.
The workers in Minnesota developed symptoms over days to months that included pain, numbness, and tingling in the extremities. The CDC also reported that the illness typically caused mild to moderate weakness in the distal lower limbs and occasionally, facial weakness. Electrodiagnostic testing showed prolonged motor distal latencies and F-wave latencies, minimal sensory nerve conduction abnormality, and evidence of mild denervation of distal muscles on EMG. Some patients had elevated CSF protein with minimal if any pleocytosis. Thoracic and lumbar MRI showed mildly thickened nerve roots and contrast enhancement.
“The leading hypothesis that we are considering is that these patients may have been exposed to a protein from the [pig] brain that has been aerosolized during the extraction procedure using that compressed air device,” Dr. Belay said. The protein in the pigs' brains may have molecular similarities to a protein in human nerves, he explained, and the antibodies produced against the pig protein may have cross-reacted with the protein in the workers' peripheral nerves.
The severity of illness in the Minnesota patients has ranged from minor weakness and numbness to paralysis predominantly in the lower extremities affecting mobility, Dr. Belay said.
In a Jan. 17 letter to the AAN, the agency asked neurologists to report diagnoses of peripheral neuropathy, myelopathy, or a mixed clinical presentation of the two conditions in people who have been exposed to pig butchering or processing to their state health department and the CDC.
To contact the CDC, call 770-488-7100.