Map of life expectancy at birth from Global Education Project.

Thursday, January 28, 2016

A couple of thoughts about Zika virus

Epidemics are scary, and often the fear is exaggerated and leads to all sorts of irrational behavior. All we need is to recall the lunacy over Ebola virus in 2014, which was never a significant threat to the United States. (Of course it was awful where it was epidemic, and the lack of sympathy here in the U.S. for people in the affected regions was at least as appalling as the misguided panic.) The flu pandemic hoax of 2010 was another excellent example.

However, the WHO's alarm over Zika virus does seem proportionate. But this is a complicated story. The virus, which is related to Dengue, has never particularly concerned anyone until now. It is indigenous to tropical Africa and southeast Asia, and was known only to produce mild symptoms. So why is it suddenly thought to be causing catastrophic birth defects in the Americas?

I don't know the answer, but I can offer a pretty good hypothesis. In areas where it has long been endemic, chances are excellent that a woman will have been infected at some time before she ever becomes pregnant, and therefore likely has long-term, perhaps lifetime, immunity. Assuming it is really true that infection during pregnancy causes microcephaly and other serious damage to the fetus, it didn't happen often enough that anybody noticed. Now, a note of caution: we are seeing a coincidence in time of the arrival of Zika in the Americas and an apparent spike in these birth defects. It's only a strong suspicion that they are related, it might be something else we don't yet know about.

In any event, if this is what is really happening, it's a variation on a classic theme. The indigenous people of the Americas were decimated by contact with Europeans because Europeans had all sorts of endemic diseases to which they had evolved relative immunity. But a population naive to an infectious disease is the formula for disaster.

In this case, it shouldn't be a long-term disaster because even as the epidemic of birth defects is raging, girls below reproductive age are getting infected, and presumably their babies will not be at risk. Of course that sanguine analysis depends on the probability of their getting infected before they ever get pregnant, and of a previously uninfected woman becoming infected while she is pregnant. Based on the African experience, we have to presume that the math works out pretty well.

But even an occasional instance of microcephaly is a terrible event. These babies will have very limited existence. So I do hope the vaccine comes soon. Meanwhile, this is a reminder that the prospect of disaster from emerging infectious disease always looms in the modern, densely populated, densely connected world. We need a World Health Organization that is well funded, highly competent, and gets full cooperation from the governments of the planet. We're short of that now.

1 comment:

robin andrea said...

Thank you for this analysis. I appreciate your thoughtful explanation of this dreadful virus.