Tuesday, March 28, 2006

Some things you can't blame on H5N1

Influenza A/H5N1 (bird flu) has shown itself more resourceful than the humans trying to stave it off. In the last seven weeks alone it has enlarged its geographic range to infect birds in 29 new countries (Jia-Rui Chong in the LA Times). It is thumbing its viral nose at the Draconian control measure of slaughtering its poultry hosts by the millions. It is now in the wild bird population, so any hope of containing it is lost. Even vaccination of poultry, once a last resort, can no longer stop its spread. And while this seems to be the new line of defense advocated by the same people who said culling was the route to take, vaccination has problems of its own.

Vaccination is a logistical nightmare since we are talking about globally distributed poultry numbers in the billions. It also has the potential to allow birds to be healthy but still infective and traipsing from farm to farm by low paid inexperienced vaccinators also may spread the disease. And of course, there's the obvious: vaccinating the wild bird population isn't possible.
"We cannot contain this thing anymore. Nature is in control," said Robert G. Webster, a virologist at St. Jude Children's Research Hospital in Memphis, Tenn., who has been studying the virus since it emerged in 1997. (LA Times)
The speed with which this virus has jumped its Asian origins has confounded and startled most everyone. Authorities in North America are now resigned to its appearance here, although when and where is unknown. Most speculation centers on Alaska where there is overlap with Asian flyways (birds fly north - south, not east west). But we should remember that birds can get around in many ways. They can be smuggled in via the rare bird trade, or even conceivably blown by storms clear across the Atlantic, one of the proferred explanations for the appearance of West Nile virus on the east coast of the US in 1999.

The remaining issue is whether the virus will find new hosts. It seems to have made the jump to some mammals relatively easily, although is not (yet) very contagious in these new hosts. Cats, dogs, martens and mink have been naturally infected and a number of other animals (mice, ferrets) have been infected in the laboratory. And of course, humans.

The H5N1 of today is not the H5N1 that made its first appearance in 1997 in Hong Kong. It has evolved genetically, exists in multiple forms and continues to change. What all this means is uncertain, but uncertainty in this instance is far from comforting:
"Something generally disturbing is going on at the moment," [WHO's David] Nabarro said. "It's certainly in the bird world, and it's pushing up against the human world in a serious way."

For most of its existence, H5N1 stewed in Southeast Asia.


The outbreak of the virus in Europe and Africa is traced to the discovery last spring of thousands of dead migratory birds at Qinghai Lake in remote western China. The lake is a crucial stopover for many birds that ultimately mix with others that migrate through Europe, Africa and Asia.

Webster suspects that the virus mutated as it circulated among the birds at Qinghai Lake, allowing it to infect wild birds more easily and hitch a ride with them on their long travels.

The genetic fingerprints of the Qinghai strain have shown up in Russia, the Middle East, Europe and Africa.

"Each morning I sit down at the computer … there's another country, another outbreak or another human case," said Nancy J. Cox, chief of the influenza branch at the U.S. Centers for Disease Control and Prevention.

"It keeps us breathless," she said.
Breathless is perhaps an unfortunate but all too appropriate turn of phrase. But maybe we will have a human vaccine developed in time (I would say, don't hold your breath, but . . . ). Unfortunately, most countries on this globe, including the US, wouldn't have the public health infrastructure to administer it in a timely fashion, so many people would go unvaccinated even in that most optimistic of outcomes.

But that's not the virus's doing. That's ours.