Disease investigators probing the mysterious neurological disorder among pork plant workers in Austin, Minn., and Indiana on Thursday said they were homing in on a specific cause.
State officials said they were broadening the investigation in Austin to thousands of former meat packers at the Quality Pork Processors plant going back a decade, to when a powerful air-compression system was installed to remove brain tissue from pig heads.
They're looking at whether pig brain tissue, liquefied during removal by the air-compression system and sprayed into the air as droplets, was inhaled by workers who became sick.
Also Thursday, the Centers for Disease Control and Prevention published the first detailed description of the disorder discovered late last year in a dozen workers at the Austin plant. They also revealed its new name -- progressive inflammatory neuropathy, or PIN -- and outlined how it is being investigated.
If testing proves investigators' theory true, they will have identified a rare new condition that could shed light on a family of similar disorders that aren't well understood.
The research "could have far reaching applications ... in terms of our understanding of the mechanism of disease," said Ruth Lynfield, state epidemiologist.
Lynfield is heading the investigation in Minnesota.
Since December, 12 meatpackers at the Quality Pork Processors (QPP) plant in Austin and two at a plant in Indiana have reported fatigue, numbness and tingling in their arms and legs, with a wide range in severity. A few are severely disabled, while others have been treated and returned to work.
Their symptoms are like those associated with a number of diseases in which the body's immune system attacks the nerves or the sheath that surrounds them.
All the workers were stationed near the powerful air-compression systems that blow brains out of pig heads at what is known as the head table, officials said. The process is no longer being used at either plant.
A widening probe
In Austin, the compressor system had been used since 1998. Lynfield said Thursday that investigators are now investigating any meatpackers who worked near the QPP head table since 1997. It's an enormous task. The plant employs about 1,200 workers, many of them immigrants. Turnover is high.
"But we feel it's important to look for prior cases," she said.
Investigators have ruled out toxins. Viruses or bacteria are unlikely because no workers reported infectious symptoms like fever before their neurological symptoms began. That leaves the brain tissue itself.
"It makes biological sense," said Mike Osterholm, an infectious disease expert with the University of Minnesota. In this case, he's working as a consultant for Austin-based Hormel Foods, which doesn't own the plant, but which uses the meat for its products. Investigators say those products are safe to eat.
An immune attack
The immune system is designed to attack entities like viruses or foreign tissue that enter the body. But for reasons that are not well understood, it is not always discriminating. Sometimes it attacks the body's own tissue, resulting in lupus, arthritis, rheumatic fever, multiple sclerosis and dozens of others auto-immune diseases.
"And pigs and humans share similarities," said Dr. Daniel Lachance, the Mayo Clinic neurologist who first recognized the cluster of unusual cases he was seeing and who initiated the investigation.
Pigs and humans are such biologically similar mammals that researchers are trying to find ways to use pig organs to replace diseased human organs. So it's not surprising that if the immune system creates cells to attack proteins from pig neural tissue, those immune cells might also attack human neural tissue as well, experts said. Lachance said that imaging tests show that many of the affected workers have inflammation of the nerve roots in the bottom half of their spinal cords.
"If you have a cross-reaction from pig neurologic tissue and human neurologic tissue, that would make perfect sense," Osterholm said.
Though humans have immune reactions to exposure to animal tissue -- allergies, for instance -- human exposure to airborne particles of pig brain tissue is a first. That makes it extremely difficult to test the exposure theory, said Lynfield.
"It has been challenging to figure out how to test that hypothesis," she said. But now experts at the Mayo Clinic and Columbia University are trying to devise ways to test pig brain tissue against the immune cells of the sick workers, she said.
It could be months before those tests are complete, she said. Meanwhile, investigators will continue to look for similar cases.
Josephine Marcotty • 612-673-7394