14/03/08

Supressing herpes doesn’t prevent HIV: another silver bullet mis-fired

Another window of hope for HIV prevention slammed shut this week, with publication of a study showing that treating herpes doesn’t prevent HIV.

There’s a very strong association between HIV infection and herpes simplex type 2 (HSV-2), especially in sub-Saharan Africa. People with HIV are more likely to get herpes, and vice versa. But because herpes is more infectious, it is far more common. Also currently incurable, herpes can erupt at unpredictable intervals, causing ulcers around the genitals and sometimes elsewhere on the body, too. Previous studies have shown that people are especially likely to catch HIV when herpes is in its active phase. If you could supress herpes outbreaks, we all reasoned, you’d reduce HIV transmission. Acyclovir, which suppresses HSV-2, has been around for a while, but it was too expensive to contemplate using on a wide scale. As the patent ran out and prices dropped, hopes rose that it might constitute a silver (or at least a brass) bullet for HIV prevention in Africa. Those hopes are now dashed.

Deborah Watson-Jones and colleagues at one of my alma maters, the London School of Hygiene and Tropical Medicine, tried giving acyclovir to roughly half of 821 HIV negative “entertainment workers” in Tanzania. The other half got a placebo. (Over a third of the women in both groups reported sex for money.) The result: the infection rate was over 4% per year in both groups (nerd alert: 4.27 per 100 person-years, rate ratio for the acyclovir group, 1.08; 95% confidence interval, 0.64 to 1.83).

The researchers fret that the dose may not have been high enough to suppress HSV-2 effectively. They question how motivated HIV negative women are to take drugs daily (urine tests suggested that lots of the women were being lazy about taking their pills). They point out that these are high risk women (background HIV prevalence even in those who didn’t have herpes was 35 percent in this population), and the HIV-HSV link may differ in high risk and low risk women. But overall, it was not a good day for those who think we can find a biomedical route to HIV prevention.

The researchers conclude that we need to do more to prevent HSV-2 in the first place. And how do you prevent herpes? Exactly the same way you prevent HIV.

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This post was published on 14/03/08 in Science.

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