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Neurological Symptoms Of
Pork Plant Workers Studied

From Patricia Doyle, PhD
From ProMed Mail
Prompted by reports of neurological symptoms among workers at 2 pork processing plants in the USA, CDC [US Centers for Disease Control and Prevention] has dispatched an urgent bulletin to all US neurologists requesting information about any similar cases they may come across. The CDC sent the bulletin to American Academy of Neurology (AAN) 17 Jan 2008; it reports that clinicians at the Mayo Clinic in Rochester, Minnesota notified the Minnesota Department of Health in the fall of 2007 about an unusual cluster of 12 patients who developed inflammatory neuropathy between November 2006 and November 2007.
All of the subjects worked in a pork processing plant in Austin, Minnesota, in an area of the facility where the pigs' heads are processed. In mid-January of 2008, there were reports of an additional cluster of patients with similar symptoms among individuals working in a pig processing plant in Indiana.
"In particular, neurologists who have diagnosed patients with peripheral neuropathy, myelopathy, or a mixed clinical presentation of peripheral/central (and, more specifically, myelopathic) involvement in persons with exposure to pig butchering or processing during the past year are asked to report this information to their state health department and contact the CDC at (770) 488-7100."
communicated by:
[2] CDC: letter to American Academy of Neurology (AAN)
Date: Thu 17 Jan 2008
Source: American Academy of Neurology (AAN) website
In the fall of 2007, clinicians at the Mayo Clinic in Rochester, Minnesota, notified the Minnesota Department of Health of an unusual cluster of 12 patients with inflammatory neuropathy occurring between November 2006 and November 2007 among workers at a pork processing plant in Minnesota. An initial investigation has revealed that they all have worked in the same area of the plant where the heads of the pig are processed. The investigation in Minnesota is ongoing and additional patients have been identified in Indiana, among workers in a similar plant. At this point an etiologic agent has not been identified.
These patients have frequently had illness onset with pain, numbness, and tingling in the extremities. The illness typically progressed with development of relatively symmetric mild to moderate weakness involving predominantly the distal lower limbs. Occasionally, facial weakness has also been observed. They often complain of difficulty with balance (ataxia). 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 (electromyography).
Of the cases in which cerebrospinal fluid (CSF) has been obtained, all have had elevated CSF protein, with minimal if any pleocytosis (such as, cytoalbuminologic dissociation). Thoracic and lumbar magnetic resonance imaging has demonstrated mildly thickened nerve roots and contrast enhancement. Time of illness progression ranged from several days to months with severity of illness ranging from mild weakness in most cases to paraplegia in one. Most have had some level of recovery.
Given the apparent close association of these patients with participation in the processing of pig head material, it is possible that similar illnesses are occurring at other pork processing plants. The CDC is requesting neurologists to provide information about patients who may have developed illnesses similar to that reported by the Mayo Clinic. In particular, neurologists who have diagnosed patients with peripheral neuropathy, myelopathy, or a mixed clinical presentation of peripheral/central (and, more specifically, myelopathic) involvement in persons with exposure to pig butchering or processing during the past year are asked to report this information to their state health department, and contact the CDC at 770-488-7100.
communicated by:
More clinical information is given here but the issues of using air pressure to extract the porcine brain in the plants where cases occurred is not mentioned and what kind of personal protective equipment was used is also not stated. - Mod.LL
[3] Neurology Today: upcoming article [7 Feb 2008]
Date: Mon 28 Jan 2008
Source: American Academy of Neurology (AAN) website
An unusual illness in a dozen workers at a Minnesota pork processing plant has state health officials concerned that the cluster could be an unknown animal-borne nervous system disease.
All of the employees worked in an area where compressed air was used to cleanse brain cavities, giving rise to speculation that the illness, health officials are calling it an unknown inflammatory polyneuropathy, may have been caused by exposure to an infectious agent in airborne brain particulate matter.
Early reports suggested chronic inflammatory demyelinating polyneuropathy (CIDP), which damages the myelin sheath surrounding nerves and typically progresses for months. However, CIDP, as a specific diagnosis, was ruled out after workers were examined by neurologists and had nerve conduction studies.
According to Daniel Lachance MD, the Mayo Clinic neurologist who is caring for many of the workers, "an astute nurse" at the plant brought the symptoms to the attention of local Austin physicians, who in turn notified the Mayo Clinic. Dr Lachance recognized the symptoms as being unusual. He told Neurology Today in a telephone interview that while the illness shares many similarities with CIDP, tests have shown it has a different signature. Unlike CIDP, which is characterized by slowing or blocking of nerve conduction, the workers' illness can be categorized only as an inflammatory response that is attacking nerve roots proximally, and peripheral motor nerves distally, he explained.
"While they do have electrophysiological evidence for peripheral nerve involvement and the disorder appears associated with a remarkable activation of the immune system, the clinical picture is different from CIDP," he said...."the syndrome is best characterized as an inflammatory polyradiculopathy."
"All of the information we have to date indicates that the general public is not at increased risk for developing this type of illness," said Minnesota commissioner of health Sanne Magnan MD PhD, in a news release. "Also, there is no evidence that the foot supply has been affected."
Symptoms appeared over several weeks to months, characterized by muscle weakness, paresthesias, especially in the legs, and chronic fatigue with a sudden onset. In most patients, symptoms have been severe enough to limit many daily activities, according to Dr Lachance, noting, for example, that many have difficulty managing stairs. Symptoms were first noted in a worker in a local soccer league when he could not continue playing. In some patients, sensory symptoms and discomfort in the neck, lower back, and limbs dominate the clinical picture, while in others, mild to moderate weakness can be demonstrated on the neurological examination. Treatment has generally consisted of observation in milder cases, while the more severely affected have been treatment with steroids or intravenous immunoglobulins.
At press time, the Minnesota state health department had not identified a cause of the illnesses. Investigators had interviewed all 12 patients, as well as workers who worked in the same area and those who did not, collecting information on work history, medical history, potential exposures, and other topics. Clinical specimens, including throat swabs and blood, were obtained from 90 per cent of those interviewed and evaluation for possible infectious agents is ongoing.
All cases of the cases involved people who worked in an area where swine heads are processed and brains removed. A compressed air system for cleaning out the brain cavities of processed swine was introduced at the plant shortly before the 1st worker complained of symptoms, and there has been concern that the illness might have been caused by inhalation of aerosolized brain tissue or a microorganism associated with this mode of exposure.
The plant quickly stopped using the compressed air system and implemented other measures to protect workers in early December 2007, and as of press time, no new cases with symptom onset since the changes were made have been reported, according to Dr Lachance.
Aerosolized blood and organ particulate in slaughterhouses and meat processing plants, referred to as "blood mist" in occupational safety circles, has long been recognized as a potential health risk and there are regulations for worker exposure in the Occupational Health Act. Even so, the symptoms do not match any known neurological illness that can be transmitted from animals to humans.
Exposure to chemical toxins at the plant has been ruled out as a cause. To date, no similar cases have been found in other states [as noted earlier in the posting, there appears to be cases in an Indiana plant using the same compressed air technique - Mod.LL] or elsewhere in Minnesota.
Because the workers were close to the brain removal area, concern was raised that the pig CNS might be the infectious vehicle. "But we did not know of any specific infectious or autoimmune disorder like this that is caused by exposure to animal tissue," Dr Lachance said, adding the disorder could be an autoimmune response to an infection. "Transverse myelitis or a brachial plexopathy after a viral syndrome, Guillian-Barre syndrome associated with _Campylobacter_ infection are the most likely models, but to our knowledge, nothing like this has even been encountered before."
Byline: Kurt Samson
communicated by:
This piece states, of note, that the use of the compressed air technique was started only shortly before cases began. The cause here may or may not be an infectious agent but could be an immunologically reactive moiety such as myelin.
More information is clearly needed here to better define this entity. - Mod.LL
In a telephone call the MN epidemiologist reported that there is no respiratory protection although full face shields are in use.- Mod.TG Patricia A. Doyle DVM, PhD  Bus Admin, Tropical Agricultural Economics  Univ of West Indies 
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