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Scientists have engineered bacteria that are normally present in the vagina to attack HIV. They say their findings could lead to an effective and cheap way of tackling the spread of the virus in both developed and developing nations.

US researchers found that in the laboratory, a modified strain of the lactobacillus bacteria could halve the rate at which HIV infected cells. If the strategy works in humans, it could provide women with a safe and long-lasting way to protect themselves from the virus, according to one of the researchers, Peter Lee of Stanford University.

"It struck me that [HIV has] to first get through the mucous membranes to get to its host," he says. "Essentially all mucous membranes of the body are colonised with normal, healthy bacteria. So why not … take advantage of these healthy bacteria to either block or inactivate viruses before they can get into a host?"

Lactobacillus already provides some protection against vaginal transmission of HIV. Research has shown that women with little or no lactobacillus have a higher risk of contracting HIV than those with high levels of the bacteria.

In this latest study, published in the Proceedings of the National Academy of Sciences, researchers gave the bacteria an extra boost by adding the gene for CD4, a protein that specifically latches on to HIV. In this way, the bacteria could act as a 'trap' for the virus, preventing it from reaching target cells in the body.

Lee says the research could lead to the creation of a small vaginal suppository that women could use regularly to provide ongoing protection. "It would be as discreet as can be," says Lee, adding that each dose could last a week or longer and could be inserted at any time. Heterosexual intercourse is the main way that HIV is transmitted, and more than 19 million women are currently infected worldwide.

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