A new study involving monkeys suggests that antiretroviral drugs used to treat HIV could also protect people from getting infected with the virus. The development is being hailed by AIDS researchers. VOA's Jessica Berman reports.

More than 33 million people worldwide are living with HIV. There were 2.5 million new infections last year alone.

Despite years of intensive effort, researchers have been unable to develop a vaccine. But antiretroviral drugs have turned HIV into manageable disease by keeping it from progressing to AIDS.

Now, researchers are finding that these drugs may be a potent weapon against the spread of HIV.

In a study involving monkeys, researchers at the US Centers for Disease Control and Prevention in Atlanta, Georgia used two antiretroviral drugs to prevent transmission of a primate version of HIV.

The scientists injected macaques with single daily doses of the antiretroviral drug FTC and then exposed them once a week for 14 weeks to a primate version of the AIDS virus. In that experiment, the drug reduced the risk of infection 3.8-fold compared to untreated primates.

The researchers then gave oral doses of FTC and another antiretroviral drug, tenofovir, to the monkeys, reducing the risk of infection 7.8-fold compared to untreated animals.

In a third experiment, the macaques were given daily shots of FTC and higher doses of tenofovir before being exposed to the primate HIV virus. Lead researcher Walid Heneine says that provided 100 percent protection, as did another regimen in which the macaques received the FTC-tenofovir combination two to three hours before exposure to the virus and 24 hours after each weekly exposure.

Heneine says the research provides a model for human use.

"The findings from this intermittent study suggests that ultimately it is possible to provide a promising new avenue for future research, where it opens up the floor for a lot of more research for intermittent dosing," said Walid Heneine.

The results of the study were published in the online journal Public Library of Science Medicine.

The Centers for Disease Control is currently conducting HIV prevention trials using antiretroviral drugs in Thailand with injection drug users, Botswana involving heterosexuals and in the United States in the homosexual community.

Lynn Paxton is coordinator of the clinical trials at CDC. Paxton says the notion of antiretroviral drug use to prevent HIV transmission is not new. She points to the use of drugs to prevent the spread of the AIDS virus from pregnant women to their unborn babies.

Paxton says the use of these drugs may soon take its place alongside other HIV prevention methods, such as condoms.

"So, we look upon pre-exposure prophylaxis as potentially a powerful new weapon that we may be able to add to this armamentarium," said Lynn Paxton.

Myron Cohen is with the University of North Carolina's Department of Medicine.

"This is not, like, business as usual," said Myron Cohen. "There are 30 to 40 million people infected. There is an urgent thing for us to have better and better tools."

Cohen commented on antiretroviral prevention therapy in the journal PLoS Medicine.