Monday, April 24, 2006

H5N1 Report -- Two Points

News of the bird flu virus is "in a trough," according to this dedicated blogmaster.

Many of us, I suspect, follow H5N1 because it's provided a good, suspenseful narrative. The cases have been few, so we can often learn the names and backgrounds of the victims. The virus has moved rapidly and surprisingly, leaping from Egypt to Nigeria. Even its pauses have surprised: Who would have thought H5N1 would kill two people in northern Iraq (and maybe a third in the middle of the country), and then drop out of sight?

The humans involved have contributed to the narrative: the hapless Indonesians, the methodical Vietnamese, the sometimes-mysterious Chinese, the stoic French. Politicians everywhere have memorized their key line: "No need to panic. Please pass the chicken."
But narrative demands ever-increasing anxiety, news of fresh disasters that heighten suspense before the inevitable announcement (whether from Jakarta or Mumbai or Los Angeles) that a cluster of cases are inarguably human-to-human.

That climactic point, by the rules of narrative, provides a natural conclusion to Volume I. Volume II then follows the pandemic itself, perhaps rounding out the trilogy with a volume on the post-pandemic world.

This is a time of watchful waiting. In a later post he notes that the current outbreak of mumps can be seen as a dress rehersal of what could be a more virulent threat in the event of a flu outbreak.

He mentioned in the first post something that I find both interesting and important: pigeons apparently will not be vectors for the virus. For some reason they are not prone to catch or carry the disease.

From the London Daily Mail:

Researcher David Swayne said: "Pigeons are not uniformly susceptible like chickens or ducks."

Infected pigeons carried the virus for about 10 days. But they were infectious for only two days and then at levels below what it would normally take to infect a chicken.
From WISTV, Columbia, S.C.:
Wildlife disease specialists have been conducting tests on the city pests, and found the birds just aren't susceptible to the virus. They're not totally immune, but research shows pigeons catch the H5N1 virus only when exposed to very high doses and even then carry the disease very briefly. Pigeons didn't even get infected after high levels of virus were squirted directly into their mouths. "So that's good news," according to one researcher.

Instead, US government scientists looking for the first signs of the deadly strain are focusing on wild migratory birds, not birds like pigeons, starlings and sparrows that stay close to home.

It makes me wonder what causes variable rates of infection from one bird species to another. How are migratory birds different from populations that stay put year-round? I'm not an expert, but respiratory endurance over miles of flying immediately comes to mind, which leads me to speculate that the immune systemns of non-migrating birds must be better. Ventilating the lungs reduces the incidence of pneumonia in humans (which is why binding the chest for rib fractures was abandoned years ago). Relatively shallow breathing, then, should correlate with a strong immune system.

So why would chickens be vulnerable? Could it be that generations of inbreeding aimed at getting faster growth, combined with the widespread use of agricultural pharmaceutical additives may have significantly compromised the immune systems of commercially raised poultry?

Ducks? I dunno. They are more than just "swimming chickens." Aren't they migratory? Miles of flying and all that.

In any case, I am reassured that the ubiquitous pigeons are apparently not at risk. (Yet. There is no way to know what direction new mutations might take.)

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