Levels of HIV come down in HIV-positive women who are also infected with herpes simplex and are being treated for it with the antiviral drug valacyclovir.

These are the findings of a study published in today's New England Journal of Medicine.

The research was conducted in Burkina-Faso in Africa and took the form of a randomized, double-blind placebo-controlled trial.

Valocyclovir is marketed by GlaxoSmithKline as Valtrex.

Dr Nicolas Nagot of the London School of Hygiene and Tropical Medicine and colleagues found that treating herpes simplex 2 (HSV-2) infections with valocyclovir reduced levels of HIV-1 RNA in both the blood plasma and the genital mucosa, with the latter being more significant.

And this effect seemed to get stronger over the three months of the study.

Once a woman has herpes, the risk of getting HIV is increased and other research studies have shown that when HSV-2 is present it increases the amount of HIV-1 in plasma and genital mucosa.

The study enrolled 140 women who were tested positive for HIV-1 and HSV-2 and were not eligible for highly active antiretroviral therapy.

The participants' levels of HIV and herpes were monitored for 24 weeks; 12 before and 12 after being randomly assigned to either the placebo or the valocyclovir treatment group.

The scientists then used statistical regression anaylsis to to work out the effect of the treatment on the genital and plasma viral loads of HIV-1 (RNA) and HSV-2 (DNA) over the period of the study. Of the 140 women enrolled, 136 were included in the analysis.

The scientists found that the group on valacyclovir showed a significant decrease in the level of HIV viral load in the genital and plasma samples, at least 50 per cent on average. There was no significant reduction in detection of HIV though, so the effect of the antiviral was to reduce rather than eliminate HIV activity.