Saturday, November 26, 2005

Sobering look at H5N1

How a virus can morph into a killer...

From MSNBC, reporting the last of a three-part series.
In the last of a three-part series, LiveScience examines how a virus jumps from birds to humans and reaches pandemic proportions.

Other pandemics

In addition to the 1918 flu, there have been two other pandemic outbreaks — defined as spreading around the world within a year of being detected — in the last century. The "Asian flu" H2N2 was detected in China in February 1957. By June of that year it had spread to the United States, causing about 70,000 deaths. In early 1968 the "Hong Kong flu" H3N2 was detected in Hong Kong and spread to the United States later that year, causing 34,000 deaths.

The H3N2 virus is still in circulation today and is included in this year's flu vaccine.

Both of these started in Asia and, like the 1918 flu, contained a combination of human and avian influenza virus.

Shifty genes

Influenza could become a pandemic threat because its genetic information is constantly shifting. The virus can change two ways -- the common and subtle "antigenic drift" and the rare but drastic "antigenic shift."

Antigenic drift refers to the continuous changes in the virus that make it slightly different than previous versions, requiring the yearly production of new vaccines. While your immune system may have developed resistance to previous versions of the H1N1 virus, for example, it can't prevent infection against this year's slightly newer version.

Antigenic shift is a major reshuffling of proteins in the virus that results in a new subtype combination of neuraminidase and hemagglutinin surface proteins, in science-speak. If this new subtype has never been seen in humans, or hasn't been seen in many years, most people won't have protection when it enters the population.

Vaccine must wait

Because the avian virus has yet to mutate to the point where it spreads easily among humans, scientists do not know exactly what characteristics to include in a vaccine. However, a study testing the immune response of the outer portion of an inactivated avian H5 strain in people older than 65 recently got under way. The vaccine is similar to the regular flu vaccine, but targeted to the avian type.

Signs of resistance

Making matters worse, the avian flu has shown signs of resistance to Tamiflu, an antiviral drug that treats the symptoms of the flu and also helps prevent infection in healthy people. It had been thought that the drug could be used to slow the spread of the avian flu until a vaccine is developed, which could take anywhere from six months to a year or more.

This last part is disturbing. Most of what I have been reading has put a lot of stock into the Tamiflu-as-weapon meme.
Read the whole article and follow the links if you want to stay up to date. Good information and education is the best defense.

No comments: