At least in mice, the "bird flu", known more specifically as H5N1, may make those who survive the disease more susceptible to Parkinson's Disease. Although flu is generally thought of as a disease of the body, H5N1 can move into the brain. How it gets there is subject to debate. Some researchers believe it moves from the GI tract to the brain along the vagus nerve (see http://en.wikipedia.org/wiki/Vegus_nerve); others, that it moves along the olfactory nerve (see http://en.wikipedia.org/wiki/Olfactory_nerve).
Researchers examined the brains of mice that survived a bout of H5N1 (mice and people both have the same about 50% survival rate). The researchers found nerve cells that make one of the brain’s key messengers (dopamine, which helps regulate movement) shut down production about 10 days after infection. These nerve cells, which are the same cells that degenerate in people with Parkinson’s disease, appear to focus all their activities on survival. By day 60, the dopamine starts to reappear, and levels are back to normal 90 days later. However, signs of inflammation in the brain remain.
Just three days into the infection, the brains of the mice showed evidence of a strong inflammatory response, and this response appeared to linger over time. Proteins that accompany inflammation, and cells that patrol the brain looking for threats, were still present and "on duty" in parts of the brain 90 days after the initial infection. At this point researchers do not know whether this inflammatory related response ever goes away.
At this point the researchers believe that the virus does not cause the disease, but may make one more susceptible to Parkinson's. They speculate that if one is already susceptible, the infection alone may be enough to trigger the disease. But, at this point, it is informed speculation.
Again, it bears repeating that toxic torts revolve around causation. Thus, in a case involving Parkinson's, it behooves counsel to consider H5N1 infection as an alternative explanation. At this point the science is still developing, but in a year or so it may be more substantive.
The report can be found at http://www.jneurosci.org/content/32/5/1545.abstract.