Influenza II

Excellent article in yesterday's Washington Post (HT: Hugh Hewitt) on the Avian flu (H5N1) and one of the researchers, Robert G. Webster, who is trying to combat the strain before it becomes a pandemic.

First the bad news:

[W]hat has Webster and other experts so worried are the 112 people who have been infected with the H5N1 "bird flu," more than half of whom have died. The fatality rate of 55 percent outstrips any human flu epidemic on record, including the epochal Spanish flu of 1918 and 1919 that killed at least 50 million people.

Why this new virus is so deadly is not entirely understood, although scientists have hints.

Influenza viruses invade cells lining the throat and windpipe, where they replicate and cause inflammation but are eventually suppressed by the immune system. In some cases, the microbe invades the lungs and leads to viral or bacterial pneumonia. Some H5N1 strains, however, have two features that make them even more dangerous.

Normally, the flu viruses can replicate only in the throat and lungs. With H5N1, however, the protein that triggers replication can be activated in many other organs, including the liver, intestines and brain. What is usually a respiratory infection can suddenly become a whole-body infection. Simultaneously, a second "defect" in the virus unleashes a storm of immune-system chemicals called cytokines. In normal amounts, cytokines help fight microbial invaders. In excessive amounts, they can cause lethal damage to the body's own tissues.

Now the good news:

So far, [t]he trait H5N1 has not acquired is the ability to spread easily from person to person.

Last fall, while analyzing a strain circulating after an outbreak in Hong Kong in 2002, one of Webster's post-doctoral researchers, Diane Hulse, made an unusually important observation.

Many ducks experimentally infected with the virus didn't die, even though the strain was highly lethal to chickens. This meant that killing infected chickens wasn't going to be enough to stop the spread of the microbe. Ducks could serve as a permanent reservoir of H5N1 virus.

The discovery by Hulse and Webster led, in part, to an extreme program Thailand mounted last November. About 70,000 investigators went into every village in the country looking for sick ducks and sampling the feces of healthy-looking ones. Flocks carrying H5N1 influenza virus were killed.

The strategy appears to have worked. Last year, Thailand had 12 human deaths from H5N1 flu. So far this year, it has had none.

It's hard to know if the H5N1 strain of avian flu will be the next pandemic, or if Webster and like-minded researchers will manage to prevent a human outbreak.

One point made by Laurie Garrett's article (see my earlier post) is that the 1917-1918 pandemic "would have been much worse had there not been milder flu epidemics in the 1850s and in 1889, caused by similar but less virulent viruses, which made most elderly Americans immune to the 1918-19 strain. The highest death tolls were among young adults, ages 20-35."

Since there has not been an outbreak of any H5N1 strains in the last century, nobody alive now has any immunity or resistance. We need researchers like Webster to keep going with the research and the intervention strategies.