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A new way of preventing the spread of HIV/AIDS and other sexually transmitted diseases is supported by research published in Nature today (5 January).

It involves microbicides, which are gels and creams that a woman applies to her vagina before sex. They kill bacteria and viruses and stop them being transmitted between partners.

Over 60 microbicides are being tested, but none has yet made it to the market. They act in different ways, for example by forming a gelatinous physical barrier, like a condom, or by changing the vagina's acidity.

Now, for the first time, researchers at Harvard Medical School, United States, propose using small pieces of genetic material, known as RNA, to kill viruses by stopping their genes from functioning.

Deborah Palliser and colleagues tested the concept on female mice, which they later infected with a type of herpes virus.

They applied a fatty substance containing a type of RNA called 'small interfering RNA' (siRNA) that can be manipulated to disrupt specific genes — in this case herpes genes.

The substance protected the mice from disease for the remaining nine days of the experiment without causing inflammation. It even protected mice when applied after they were infected.

The researchers say that, while more studies are needed to show, among other things, how long protection lasts and whether menstruation affects protection, the findings suggest that a human microbicide using siRNA might not need to be applied just before sex, as now thought.

This, they add, could solve one of the main problems of microbicides: making sure women use them consistently.

The results could have implications for efforts to stop the spread of HIV/AIDS if an effective siRNA microbicide can be developed against HIV rather than herpes.

In addition, the ulcers herpes causes greatly increase people's vulnerability to infection with HIV. Preventing herpes, might therefore help reduce HIV transmission.

Link to full paper in Nature

Reference: Nature 439, 89 (2006)

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