Diseases are hard to diagnose, and can be even harder to trace

By Josephine Marcotty, Star Tribune

Last update: December 4, 2007 - 10:56 PM

The neurological illness that has stricken 11 workers at an Austin pork-processing plant has raised questions about whether it was caused by an infectious agent, a toxin, exposure to animal tissues, or some unknown factor.

Health officials won't know the answer until the investigation -- which could take months or years -- is complete. Or they may never figure it out.

The situation is confounding because the workers share some symptoms of a rare autoimmune disease, chronic inflammatory demyelinating polyneuropathy (CIDP), which is not well understood and can have many triggers. And they were working with raw animal tissue -- which can be a source of new and dangerous diseases, such as mad cow disease.

What is an autoimmune disease?

It is a condition that occurs when cells deployed by the body's immune system attack healthy tissue.

Normally those cells help protect the body from bacteria, viruses, toxins, cancer cells or other harmful agents.

But in patients with an autoimmune disorder, the immune system can't tell the difference between healthy tissue and foreign invaders . What causes that reaction in some people is unknown. There are more than 80 types of autoimmune disorders, including multiple sclerosis and arthritis.

What is chronic inflammatory demyelinating polyneuropathy (CIDP)?

This rare autoimmune disease, affecting two out of every 100,000 people, is very difficult to diagnose. It gradually damages the tissue sheath surrounding nerves in arms, legs and the trunk.

What triggers CIDP's immune response is unknown. It is the chronic form of Guillain-Barré Syndrome (GBS). But GBS, which develops more rapidly, has some known triggers. It first gained wide public notice in 1976 when it struck some people who received swine flu vaccine. Officials say five of the 11 workers in Austin have had CIDP diagnosed.

What are transmissible spongiform encephalopathies (TSEs)?

TSEs are diseases in people or animals caused by abnormal proteins called prions. That includes Chronic Wasting Disease and Variant Creutzfeldt-Jakob disease (VCJD) -- the human form of mad cow disease. They are chemically the same as normal proteins, but they transform normal proteins into brain-wasting agents, creating sponge-like holes in infected brains. Health experts say the Austin illnesses so far do not resemble prion diseases.

Sources: University of Minnesota Center for Animal Health and Food Safety; National Institutes of Health