Women infected with both HIV and genital herpes show lower levels of the AIDS virus in their systems if the herpes is treated.

Researchers tested 140 women in Burkina Faso who had both infections. More than 100 received a medication, valacyclovir, to treat herpes and the rest took placebo pills.

"The results of the trial are striking," said the study's lead author, Dr. Nicolas Nagot of the London School of Hygiene & Tropical Medicine.

"They show that valacyclovir significantly reduces the frequency and quantity of HIV detectable in genital secretions and, in addition, reduces the quantity of HIV in the [blood]."

The benefit appeared to grow stronger over the three months of follow up, the researchers said in Thursday's New England Journal of Medicine.

The findings could open new approaches to preventing the spread of HIV and managing patients who are infected by both viruses. It is estimated that 50 to 90 per cent Africans who have HIV also have the virus for genital herpes, HSV-2.

Previous studies have shown that people with HIV and herpes show more viral replication and HIV cells in the blood and vaginal area.

Doctors tended to put less emphasis on treating genital herpes because it is less dangerous than HIV.

Drugs affordable

Besides valacyclovir, the drugs acyclovir and famciclovir also can be used to treat HSV-2. All three drugs are relatively affordable and carry few side-effects, the researchers said.

In 2005, an estimated 4.1 million people were newly infected with HIV, mostly through heterosexual intercourse.

The infections show that behavioural changes do not always work, so it is important to look for other ways to reduce the biological susceptibility to HIV, Nagot said.

Microbicide gels that women could apply themselves without the knowledge of their partners and male circumcision are some of the strategies that are under investigation for preventing HIV infection.