Friday, November 02, 2007

What's in the soil?

Ever wondered why HIV is so prevalent in Africa? Could it have something to do with the continent's geography? Sounds ridiculous, maybe, but there's at least some evidence to support the idea. Check out my new post on the subject at 60 Second Science...

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3 Comments:

Blogger Bob Nease said...

The "third wave" of the HIV epidemic (i.e., among non-IV drug-using heterosexuals) never took off in the U.S. because of the lopsidedly low female-to-male transmission rate. It's just really hard to get the epidemic rolling when women can only transmit the infection back to men at a tenth of the rate.

The extraordinary HIV prevalence in Africa suggests that the female-to-male transmission rate is higher there. One possible explanation is the far-lower prevalence of circumcision in Africa. It's biologically plausible that an intact foreskin would increase the rate of transmission to men -- there's a nice, warm, protected landing pad for the virus.

And an association between circumcision and HIV prevalence does in fact exist. A recent analysis from the CDC found that areas with the highest circumcision rate have the lowest prevalence of HIV.

But as we all learned in science class, association isn't causality. What separates the men from the boys (or in this case the foreskin from the men) would be a randomized controlled trial of circumcision. And believe it or not, such a trial was done in South Africa and Kenya. The results suggested that male circumcision cut the incidence of HIV infection in half.

What would be really interesting is to know whether Foster's results hold up after controlling for circumcision rates. And if they don't (because selenium tends to be high when circumcision rates are high), another interesting question arises: why the association between selenium and circumcision?

12:23 PM  
Blogger Michael Witten said...

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1:14 AM  
Blogger Michael Witten said...

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10:55 AM  

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