Avian Flu Kills By Overstimulating the Immune System

Researchers are finding that the H5N1 bird flu is dangerous to humans -- even in its current genetic makeup -- because it does what the 1918 pandemic flu did: provoke the body into an over-the-top immune-system response. According to researchers at Hong Kong University, an H5N1 infection prompts a "cytokine storm" of inflammatory cells -- an overreaction by macrophages (the immune system's first-responders). These cells rush to the infection site to kill germs and infected body cells, until a "cavalry charge" of antibodies can arrive.

The overzealous cytokines, it turns out, kill friend and foe alike, weakening blood vessels, allowing fluid leakage and causing a drop in blood pressure. This process cascades into pneumonia, hemorrhage and shock. Even with intensive care, some victims die due to respiratory and organ failure, as did millions in 1917-18.

It's possible that immune-system inhibitors and inflammation-reducing drugs (such as steroids, ACE inhibitors and statins) could help. For now, the best treatment for an H5N1 infection is Tamiflu, taken within 48 hours of infection. The problem, of course, is that it usually takes longer than 48 hours for the infection to become obvious. Due to the number of human H5N1 infections in Southeast Asia, the WHO, NIH and regional researchers are discussing developing clinical trials there, in which a variety of antiviral treatments will be tested.
[HT: WSJ (subscription req'd)]

Pharma companies are already working on vaccines targeted specifically against H5N1, and Sanofi's vaccine "is showing promise" in early trials.