Tuesday, March 27, 2007

Vigilance on Avian Flu

Foreign Affairs, not exactly known for wild alarmism, repeats their call for a greater focus on the threat of avian flu:
More than a year and a half ago, Foreign Affairs published three articles that sounded a clarion call to prepare for the next pandemic. They warned that another pandemic could occur at any time and at a staggering cost to human health and the world economy. These facts remain incontrovertible. At the time, many public health scientists believed that recent outbreaks of the H5N1 influenza virus in birds in Asia, Europe, and Africa, with occasional infections in humans, were precursors to the next pandemic. They still do today.
Here's a link to what I wrote at that time. Why is the threat of an avian flu pandemic serious business?

No one can predict when the next pandemic will occur or how severe it will be. But it will occur for sure, and because of the interdependence of the global economy today, its implications will reach far beyond its toll on human health. A recent study by the Lowy Institute for International Policy, which provides the most comprehensive estimate yet, found that a mild pandemic similar to that of 1968 would kill 1.4 million people and cost approximately $330 billion (or 0.8 percent of global GDP) in lost economic output.
"Posh!" you say. "Bird flu only affects birds and unfortunate chicken farmers!" That's perhaps true...today. But it may not stay true forever. Again, from the Foreign Affairs article:
For decades, scientists believed that the only way for an avian influenza virus to become transmittable between humans was through a process known as reassortment. Reassortment occurs when an avian virus and a human virus both infect the same cells of an animal (a pig, for example) or a person and swap genes, creating a new virus adapted to humans. (This is how the 1957 and 1968 influenza pandemics began.) Over the past two years, however, studies of tissue samples from 1918-19 influenza victims have suggested that an influenza virus can also become a pandemic strain after undergoing genetic mutations of its own. Recent studies of the virus' genetic material have demonstrated that the 1918-19 virus likely evolved by a process known as adaptation, a series of critical mutations that rendered it capable of being transmitted between humans.

Although it is impossible to know for sure whether H5N1 will ever evolve into the next human pandemic virus, more and more of the genetic changes documented in the 1918-19 virus have also been found to have occurred in recent H5N1 strains affecting both birds and people.
And this, from a NY Times article today on the very same subject:
The Qinghai strain has a mutation known as PB2 E627K. (The abbreviation can be read this way: at position No. 627 on polymerase basic protein 2, the amino acid called glutamic acid, abbreviated by scientists as E, has been replaced by lysine, known as K.)

The change helps the virus grow at the temperatures found in human noses, which are cooler than the insides of birds’ intestines.

To give a sense of how important such a tiny change can be: switching just one of the 1,255 amino acids in the SARS virus protein that attached to cells in the masked palm civet, a relative of the mongoose that is sold in wild-meat markets in Asia, allowed it to attach to human cells.

In avian flu, two mutations known to help viruses spread more easily — because they attach to the receptors in human noses and throats instead of those deep in the lungs — were found in outbreaks in Azerbaijan and Iraq in 2006. But those outbreaks were snuffed out.

Another mutation, increasingly common in Egypt, where the disease is still raging through poultry and occasionally infecting humans, is called M230I. Scientists do not know what it does, but its persistence is worrisome, says Henry L. Niman, a Pittsburgh biochemist who runs a Web site tracking the genetics of flu cases.

All the human cases in Egypt with M230I have been fatal, Dr. Niman said, and those without it have not been, although that may be coincidence.

Mutations that confer resistance to Tamiflu have also been found in Egypt.
In other words, the virus is actively mutating as it spreads throughout human and poulry populations. As should be evidenced from these and prior discussions, only two things need change about avian flu to dramatically increase it's lethality among humans. One, it has to spread more easily to and among people. Second, it needs only to be slightly more lethal. Avian flu appears to be well on it's way to accomplishing the first. What about the second? If you want some ideas about what we should be doing in the meantime (beyond eradicating infected bird populations as quickly and thoroughly as possible) see my original post and another post I wrote on the necessity of doing away with factory farming.

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