Thursday, March 03, 2005

"Chicken Flu" and the bioterrorism drumbeat

A reader has linked in Comments to a Commentary published February 28 in the LA Times by Wendy Orent, "'Chicken Flu' is no big peril" (hat tip, Akka). Orent's argument goes something like this.

Earlier this year we heard a lot about the possibility of a pandemic because of the explosive spread of H5N1 among poultry in southeast asia combined with the potential for mutation into a form that could pass easily from person to person. Then came the flu vaccine shortage. But the flu season has been milder than usual and there has been no pandemic yet. So Orent takes CDC Director Julie Gerberding to task for spreading the alarm despite the fact that there is no fire. This is the opposite position we have taken here, taking Gerberding to task for not spreading the alarm because there is smoke.

There is more to Orent's argument, of course. She notes that virologist Jeffrey Taubenberger, who has studied the genetic make-up of the 1918 pandemic virus, believes it did not acquire its HA gene directly from birds. She does not mention that he believes the 1918 was already "mammalian adapted" (see Taubenberger, J. Virology, August 2002). This is an important point because the H5N1 currently circulating in southeast asia has already adapted to an impressively wide range of mammalian hosts, including humans.

I don't disagree with her point that the high virulence for chickens is likely a by-product of large industrial farming practices, a point made here a number of times. So what? Orent's claim that the current H5N1 virus has "evolved to kill chickens" is incorrect. It has evolved to reproduce. Killing chickens is an irrelevant by-product. It does nothing to ducks. This is typical of most avian influenza viruses: they are of low pathogenicity. The fact that this one is highly pathogenic to poultry is unusual and likely a consequence of the crowded conditions she cites.

The only thing needed now for a pandemic is a change to allow efficient human-to-human transmission. If the virus does mutate in that fashion and retains only a small fraction of its current virulence for humans, we are in for a big problem. Note that it is already highly pathogenic to humans, with a high case fatality that is much different than the 1% she cites for the 1918 virus. And her argument has a flip side: consider the havoc wrought by a virus that only had a 1% mortality. Suppose this one has a case-fatality of only 5% or 10% instead of the current figure which is in excess of 70%?

Finally, her claim that it is "faulty logic" to expect that the absence of the heightened human crowding accompanying World War I troop movements would allow a pandemic virus to develop is itself an astounding case of defective logic. Looked at purely as a matter of logic, this amounts to the claim that crowding in humans is a necessary (not just a sufficient) condition for the mutation of a virus to virulent form. This is not a matter of logic but of what the facts might or might not be. Moreover she confuses transmissibility with virulence. This virus has already developed terrible virulence for chickens and humans. The only thing missing is easy transmissibility, for which crowding is not a selector.

But the most bizarre part of Orent's argument comes at the end. Don't worry about bird flu, she says. What we really should be worried about is a resurgence of pneumonic plague (The Black Death). She cites a reported outbreak in a mine in the Congo:
The logic is clear: It's human disease factories and not a virus mutating among chickens that should command our attention. We ought to be more worried about conditions such as the Congo mine, where sick people huddle with healthy people and deadly disease can evolve to terrifying effect, than about an avian flu threat that most likely will never come to pass.
But there is no logic here, much less clear logic. There is only a dubious claim. I agree we should be worried about human disease factories "where sick people huddle with healthy people and deadly disease can evolve to terrifying effect," but I strongly disagree with her illogical path to complacency about "an avian flu threat that most likely will never come to pass." Wishing won't make it so.

Orent has a history of beating the bioterrorism drum. This is another example of how that preoccupation is destroying genuine public health concerns.