This article appeared in MMWR on Feb. 8, 2008.
The Minnesota Department of Health conducted an investigation to characterize the outbreak of unexplained neurologic illnesses among workers in a swine slaughterhouse in southeast Minnesota. As of January 28.2008 12 workers at this plant had been identified with progressive inflammatory neuropathy (PIN). Median age of the 12 workers was 31years, and six patients were female. All 12 patients that had PIN reported being healthy before the onset of neurologic symptoms.
The symptoms of PIN reported by workers ranged from acute paralysis to gradually progressive symmetric weakness over periods ranging from 8 to 213 days. Eleven patients had evidence of axonal or demyelinating peripheral neuropathy by electrodiagnostic testing. A sample of cerebrospinal fluid was obtained from seven patients, and they all showed elevated protein levels with no or minimal pleocytosis. Five of these patients had evidence of inflammation on a spinal MRI (4 patients in peripheral nerves or roots and one patient in the anterior spinal cord).
All 12 patients with PIN reported either working at or having regular contact with an area known as the warm room where swine heads were processed (head table). Thus, a case-control study was conducted among the plant’s workers to identify the specific risk factors associated with neurologic illness. Ten patients out of the 12 initial reports of PIN were chosen that had confirmed or probable PIN. Also two stratified control groups were formed: 1) a random selection of 48 healthy warm-room workers and 2) all 65 healthy head-table workers. Blood samples and throat swabs were collected from all consenting case patients and controls. As of Jan 30, 2008 the lab investigations had not identified any infectious agent from the blood and throat swab specimens that would explain the occurrence of PIN.
The results of the case-control study highlighted several important aspects that could contribute to PIN among the workers. Seven of the ten case-patients were significantly more likely to have worked at the head table than warm-room controls (12 of 48). Also, case-patients were more likely to have removed brains or remaining skeletal muscle from the pig head (4 of 7) than head-table controls (8 of 65). Importantly, the illness was not determined to be related to previous travel outside or within the US, nor related to exposure to chemicals, fertilizers, insecticides, or use of medications and receipt of previous vaccinations.
An environmental assessment of the plant was conducted the better understand the methods of processing as well as the personal protective gear used by the workers. The investigators found that a compressed air device was used in the plant to harvest brain tissue from pig heads at the head table. The compressed air disrupted the brain material into a liquefied form that made it easier to remove the brain. However, this technique caused splatter possibly including aerosolized brain material to which the workers operating the device and other nearby might have been exposed. In response to this investigation, the plant suspended harvesting of brains and instituted additional protective gear that included face shields and long sleeves.
To date, three plants in the US used compressed air to remove pig brains including one in Nebraska and one in Indiana. Nebraska plant did not have reports of Pin, but the Indiana plant had similar histories of PIN as in Minnesota for workers exposed to head processing activities at that slaughterhouse. As a result of this, all three plants have stopped using compressed air devices for brain removal.
The FDA inspected the pigs processed by these plants and no food risk was identified for the general population. This investigation in Minnesota suggests that in the process of using the compressed air device, workers might have been exposed to aerosolized brain material through inhalation or contact with mucous membranes. The current hypothesis for development of PIN in the swine plant is that worker exposure to the aerosolized pig neural protein might have induced an autoimmune-mediated peripheral neuropathy. Thus, is it just a cross-reaction in the immune system caused by the similarity of the pig neural proteins to human proteins?
Mysterious happenings like this are fascinating to me! I think that a cross-reaction in the immune system is a great explanation.
ReplyDeleteI thought it was interesting too. It seems that repeated exposure to the pig neural protiens would result in a more destructive immune response. I wonder if the affected people were checked for presence on autoantibodies which could serve as an indicator of risk for PIN for other people that have worked at the headtable or under similar situations.
ReplyDelete