When 21 slaughterhouse workers at an Austin, Minn., pork plant came down with a mysterious neurological disorder in 2007, it prompted a nationwide investigation into the unique autoimmune disease.
Now, nearly three years later, researchers are reporting that they're beginning to piece together the puzzle. In a study published Monday in Lancet Neurology they confirmed an initial theory -- that the workers had inhaled pig blood and brain tissue sprayed into the atmosphere by high-pressure air hoses.
But they also found that many other meatpackers who worked in the same area and inhaled the same foreign tissue did not get sick. Together, the findings raise a more profound question: What was the difference?
"That is the great unknown," said Dr. Daniel Lachance, a Mayo Clinic neurologist who was one of the first to identify the disease and has studied it ever since. "There are many, many instances in medicine where people have exposure but they don't get sick."
The study, led by Lachance and co-written by researchers at the Minnesota Department of Health, is the first detailed look at what happened to the 21 meatpackers at Quality Pork Processors and three from another pork processing plant in Indiana who developed the neurological disease.
It confirms what investigators hypothesized at the time -- that the workers' immune systems reacted to pig protein they inhaled from bits of brain tissue and blood floating in the air. They all worked near a table where a high-pressure air hose cleaned the brain from pig skulls.
In 2007, 11 workers reported unusual and sometimes debilitating pain as well as weakness and numbness in their arms and legs. Eventually, 24 workers were identified with the same symptoms.
Lachance found that, in all those cases, the workers' immune systems attacked their nerves. It is the same kind of process that occurs in many other autoimmune diseases, including lupus, arthritis and multiple sclerosis. But in those diseases, what triggers that autoimmune response is unknown, as is why it happens in some people but not others.
In the pork plant workers, the trigger was clear -- pig protein that found its way into their blood.
"It's rare to have an autoimmune disease where you know the source of the attack," Lachance said. That's one reason why researchers have found the case so intriguing.
Now, Lachance has found that other workers in the plant had the same immune response -- they, too, developed the same kind of immune cells, called antibodies. But those cells did not turn on their own bodies, as they did in the workers who became ill.
Proximity played key role
He studied blood samples from 100 workers in the plant who did not get sick, and found that one-third had the same antibody profile as the 24 who did get ill. He also found that the closer they worked to the head table, the more likely they were to have a strong antibody response.
The investigation is still underway. Researchers at the University of Minnesota and at Columbia University in New York City are studying which protein triggered which antibody, and why some workers were affected and others were not, said Dr. Aaron DeVries, a medical epidemiologist at the state Health Department who co-wrote the paper published Monday.
Two of the patients who were the most severely affected will always have some disability, Lachance said. The rest have recovered, although all still report some symptoms -- primarily pain or tingling. That too, is mysterious, he said.
"It is becoming more and more difficult to understand why that is," he said. "But from every objective measure, they are all getting better."
Josephine Marcotty • 612-673-7394