The Case of the Curious Disease

Three years ago, when a strange illness surfaced among workers at an Austin slaughterhouse, state health investigators and researchers from the Mayo Clinic stepped in to search for the cause. Their sleuthing not only got workers back on the job, it also resulted in the discovery of a new disease.

CAROLE BOWER watched as a young man slowly trudged toward her up the stairs to the third-floor medical clinic, each step an energy-sapping effort. Bower, the head occupational-health nurse at Quality Pork Processors (QPP) in Austin, treats employees’ health issues every day. Soft-spoken and professional, dressed in nursing white, she’s just the sort of soul you’d want to talk to if you were sick or injured, and QPP employees typically go to her for everything from cuts and strains to flu symptoms. But what she was seeing now was of a different order, and the young man’s condition contributed to her already growing sense of concern. ¶ It was late summer 2007, and over the past few months she and the five other nurses in the clinic had seen several previously healthy employees reach such states of incapacitation that they could barely drag themselves up the stairs. They all complained of similar symptoms—various levels of fatigue, tingling in their fingers, the inability to stand for long periods of time, pain, headaches, difficulty walking—and taken as a pattern, the complaints indicated something ominous. Bower had a hunch it was coming from somewhere on the processing floor.

She referred her patients to the Austin Medical Center, which is part of the Mayo Health System and is located across the Cedar River from QPP, just behind the Spam Museum. She also notified the medical center’s chief of staff and QPP’s senior management. As it turned out, several others with similar complaints had been visiting the center since the fall of 2006, getting care from a variety of doctors. One person, however, had spoken with almost all of them: Carol Hidalgo, the medical center’s Spanish interpreter.

Hispanic immigrants, according to the U.S. Bureau of Labor Statistics, comprise the largest proportion of workers in the nation’s meat and poultry industry. Mostly young and male, they are attracted to the industry because it requires little English. Indeed, the 1,300 workers at QPP resemble a mini United Nations, and many of them count Spanish as their primary language. Hidalgo, who regularly interacts with Spanish speakers who work in Austin’s meat-packing industry, called the doctors’ attention to a disturbing fact: All of these patients exhibiting the suspect symptoms worked at QPP.

MOST OF US WHO EAT MEAT prefer to think of beef, pork, or chicken as predictably shaped protein sources that originate at grocery stores, neatly packaged in plastic and Styrofoam. But the reality of the abattoir is far from neat. At QPP, for example, 19,000 live hogs, delivered by an endless succession of trucks, are slaughtered every day and moved through what is basically a “disassembly line,” emerging at the other end as cuts of meat. Many cuts go directly to the adjoining Hormel plant to be processed and packaged as everything from pork chops to Spam. They are then sold across the country and around the world.

The work at QPP is physically demanding and sometimes dangerous, performed in bloody, greasy surroundings marked by a pungent odor. The most common injuries in this industry are cuts, strains, and repetitive-stress injuries, such as carpal tunnel syndrome. However, the situation at QPP clearly indicated something different to the doctors in Austin: To them, it resembled a condition called inflammatory neuropathy, a general term used to describe what happens when nerve tissue is inflamed due to an immune-system response.

In September 2007, doctors at the Austin Medical Center brought in Daniel Lachance, MD, the then consulting neurologist from the Mayo Clinic in Rochester. Professorial-looking and articulate, Lachance is a specialist in neuro-oncology and neuro-immunology, especially autoimmune nervous-system disorders evaluation and research. After reviewing the cases, he recalled seeing a patient three years prior who had similar symptoms. Another patient with similar symptoms, seen in 2006, had been treated with steroids. The treatment helped alleviate the symptoms, but the patient got sick again after returning to work.

In the field of neurology, doctors routinely see individuals with puzzling symptoms. That’s especially true at the Mayo Clinic, which attracts people from around the world seeking diagnosis and treatment for exotic illnesses. Yet, this was a cluster of patients from the same area, with the same symptoms. “In the general population,” says Lachance, “the frequency of people with inflammatory neuropathy is two to five in 100,000. But we were in a town of 20,000, and there were 12 cases. We knew we had a big problem here.”

 

IN LATE OCTOBER 2007, the Minnesota Department of Health (MDH) received calls from the Austin Medical Center, the Mayo Clinic, and Carole Bower, all reporting the mysterious disease among QPP workers. That set in motion parallel investigations, with public-health epidemiologists hunting for the environmental source of the illness while Lachance and his colleagues sought to pinpoint its physiological trigger.

Twelve sick people may seem a small number by outbreak standards. Yet because of the way food is now distributed—from a few central sources to retail outlets around the world—a problem in a single food-processing plant can have far-reaching and lethal health consequences. Was it safe to eat pork processed at the Austin plant? And equally important, how many QPP workers had been exposed to this unknown and potentially crippling pathogen? “There were new people coming down with it,” says Ruth Lynfield, the state’s chief epidemiologist and the MDH’s medical director, who led the investigation, “and these people were quite ill, so we were concerned about the ongoing risk.”

“It was heartbreaking to see,” says Richard Morgan, president of the United Food and Commercial Workers Union Local 9. One man, he recalls, spent time in the hospital and was briefly confined to a wheelchair due to the pain. Another afflicted QPP employee told CNN, “The doctors couldn’t believe how fast it came on. In a four-month period I went from being able to walk to not being able to walk. I’m only in my middle thirties—who needs to be in a wheelchair in their middle thirties?”

The list of culprits behind such an outbreak can at first appear endless. Was a cleaning chemical or bacteria festering in the ventilation system to blame? Maybe the disease was coming from the pigs themselves—via a parasite or something akin to mad cow disease, a new “mad pig” malady. Did the QPP employees contract the illness at work, or were they exposed to something at an outside gathering?

To answer such questions, public-health investigators form hypotheses that are continually tested and refined. “It takes tenacity and great patience,” says Lynfield. “You have to look under every rock. We look at broad boxes and categories of suspected pathogens and contaminants and keep narrowing the search down. We’re like crime detectives—only we work with ‘micro villains.’ ”

THE GROUP ASSIGNED by Lynfield to tackle the problem included medical epidemiologist Aaron DeVries and veterinarian Stacy Holzbauer, a Centers for Disease Control and Prevention epidemiology field officer assigned to Minnesota. Based on information gleaned from employees’ medical records and from interviews they’d conducted with workers, DeVries, Holzbauer, and their colleagues developed a working hypothesis. They then tested QPP workers who were sick and, equally important, tested several people from the plant who were not sick—creating a classic control group. QPP’s management was “incredibly cooperative,” despite the potential implications for the business if something gruesome was discovered, says Lynfi eld: “I give [QPP’s president] Kelly Wadding a lot of credit. He was really concerned about the workers.”

Slowly, the investigators sifted through the evidence. They reviewed scores of infections that could come from hogs or humans, but nothing seemed to produce the symptoms they were seeing. The disease wasn’t consistent with food-borne illness, and it didn’t spread from person to person. No family members of the victims were ill, nor was anyone in the surrounding community similarly afflicted. Investigators also used their CDC network to query veterinarians and neurologists across the country who might have seen such an illness. They set up a public hotline for people to call if they thought they had similar symptoms.

On November 30, 2007, investigators uncovered some vital clues toward solving the case while taking an observational tour of the QPP plant. Cloaked in the garb that plant workers wear—hard hats, white coats, rubber boots and gloves, hearing protection, and hairnets—the group reviewed each step of the production process. Accompanied by Wadding, they eventually reached the “head table,” where workers removed the meat from each pig head and extracted the brains from the skull. (In the meatprocessing business, almost nothing goes to waste, and there is a surprising demand for brains. Pork brains are a stir-fry staple in China and Korea, and canned pork brains mixed with milk gravy can be found in many southern U.S. supermarkets.)

 

Roughly 30 people were working at stations around the 16-by-20-foot head table. Those workers tasked with “blowing brains” would, in rapid succession, insert severed pig heads into a device that pneumatically blasted the brains out of the skull—each blast sending up a mist of brain matter into the surrounding air. Many pork processors simply split the skull with a large knife or a band saw, but QPP had installed this system nearly 10 years before because, according to Wadding, it was “more efficient and easier on the worker.” It was also, presumably, safer than using knives.

But the mist hanging in the air around the head table alarmed Lynfield and her colleagues. “I said, ‘What should we do about Animal Health about the disease. Two such plants surfaced: one in Nebraska, where one employee was sick, and the other in Indiana, with seven ailing workers. Of the 26 plants canvassed in the United States, the Nebraska and Indiana operations were the only others that removed brains with compressed air. On December 3, 2007, Lynfield held a press conference in Austin to announce that the illness was likely an inflammatory neurological disease and that it probably was related to removing brains from hogs’ heads with compressed air. They had found the source of the problem in little more than a month’s span, yet the cause remained a mystery. How could pigs’ brains actually cause such an illness? this?’ ” she recalls. Wadding immediately ordered a halt to the brain-blowing process. “It was easy,” he says, in retrospect, “to take the brains out of the mix.” The company simply stopped selling the organs.

When brain blowing ended, so did new occurrences of the disease. Lynfield and her team seemed to have found the root of the problem: Statistical analysis later showed that those individuals who worked 10 feet or less from the brain-removal device were 14 times more likely to have the disease than those who worked farther away. Hoping to identify workers with similar problems at other pork-processing plants, the investigators alerted the World Health Organization and the World Organization for Animal Health about the disease. Two such plants surfaced: one in Nebraska, where one employee was sick, and the other in Indiana, with seven ailing workers. Of the 26 plants canvassed in the United States, the Nebraska and Indiana operations were the only others that removed brains with compressed air.

On December 3, 2007, Lynfield held a press conference in Austin to announce that the illness was likely an inflammatory neurological disease and that it probably was related to removing brains from hogs’ heads with compressed air. They had found the source of the problem in little more than a month’s span, yet the cause remained a mystery. How could pigs’ brains actually cause such an illness?

IT FELL TO LACHANCE and his colleagues at the Mayo Clinic to treat the patients with the disease and assess its pathology. From the international dragnet, a total of 29 people had been found to have the illness—the seven in Indiana, the one in Nebraska, and 21 in Minnesota, all at QPP. By April 2008, Lachance and his colleague P. James B. Dyck, MD, a peripheral neuropathy expert, had subjected most of the a ected QPP workers to a battery of procedures, including MRI scans, blood tests, electrodiagnostic studies, and cerebrospinal-fl uid exams.

For a scientist, the case was a strange and exciting puzzle. “We all realized,” Lachance says, “that this was something that was really quite novel, something that had never been seen before, at least not in the modern era, that we were aware of.”

The working theory was that pig brains in a fine mist had somehow entered the bloodstream—most likely via the respiratory system. The tests and subsequent research seemed to rule out any type of infectious disease. The most likely cause of the illness, Lachance and his colleagues posited, must be an autoimmune response—the body’s defense system was, for some strange reason, attacking itself.

The human immune system identifies harmful invaders (called antigens) by their unique protein sequences and then produces antibodies that bind themselves to and destroy the antigens. If bacteria enter the body through a cut, for example, the body identifies them as foreign and possibly harmful and then releases antibodies to attack and destroy them. Sometimes, however, molecular similarities exist between antigens and healthy tissue, causing an immunologic overreaction in which the antibodies attack not only the antigens but also any healthy cells that might resemble the antigen. Scientists call this “molecular mimicry,” and it’s one of the leading theories explaining why the immune system turns on its own body in diseases such as multiple sclerosis, rheumatoid arthritis, lupus, and type 1 diabetes.

 

Genetically speaking, pigs and humans are very similar (that’s one reason doctors can transplant porcine heart valves in humans). Lachance theorized that the sick slaughterhouse employees had somehow absorbed aerosolized pig-brain tissue through their lungs or via small cuts, and the resulting immune responses targeted not only the foreign substance but, in a case of mistaken identity, the workers’ own healthy nerve tissues as well.

This wasn’t the first instance in which scientists had found that animal neural tissue could triggered an autoimmune attack on the human nervous system. In 1885, Louis Pasteur and Émile Roux developed the first vaccine for rabies, created by harvesting the virus from the nerve tissues of rabies-infected rabbits. Pharmaceutical manufacturers now use different methods, but that early vaccine brought with it a wide range of possible side effects, including the demyelination of the central or peripheral nervous system. Such damage to the myelin sheath, which covers nerve fibers like insulation on an electrical wire, can result in neurological dysfunction, cognitive problems, and even coma.

Hoping to confirm the autoimmune diagnosis, Lachance conducted a handful of tests. One indicated inflammation of nerve roots and the meninges, the membranes that covers the brain and spinal cord. Nerve biopsies showed inflammation, demyelination, and nerve-fiber degeneration. And a final package of antibody tests developed at the Mayo Clinic confirmed Lachance’s belief that the antibodies were specifically targeting the nervous system. The combined picture that resulted from all of the tests proved the discovery of an autoimmune disease that had never been reported anywhere else in the world. Lachance and his colleagues ultimately called it “sensory predominant polyradiculoneuropathy.”

Yet in science, unlike in the detective world, a case is never completely closed. Discoveries and solutions lead to further questions that may never be answered. For example, some workers in the QPP control group tested positive for the antibody yet remained healthy. Why? Lachance says that workers’ proximity to the brainblowing device was key. Though many were exposed, only those closest to the process became ill.

And given that QPP had been blowing brains for 10 years, why didn’t the illness crop up sooner? Some workers suggest that the problems appeared in greater numbers after changes were made in the processing operations. But, says the CDC’s Stacy Holzbauer, “Because there were so many variables—different workers of different heights, a fan on or off, for example—we can’t prove or disprove that theory without setting up a controlled test. And we never want to reproduce that problem again.”

“It was an interesting experiment of nature,” says Lachance. “It’s unlike anything I’ll ever experience again in my career.” Yet what investigators learned may also someday help advance new research into autoimmune diseases or assist doctors in understanding neurological disorders. “Science evolves over time in unexpected ways,” Lachance says.

But for the QPP workers who fell ill, the most important piece has been getting their health and jobs back. To various degrees, all of the people who fell victim to the mysterious disorder have recovered. “Most people are working again,” says the union’s Richard Morgan, though not all are at full capacity. He adds, “Hats off to the folks who put the pieces of this nasty little puzzle together.”

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