Main | Wednesday, February 04, 2009

Does Oral Sex Protect Against HIV?

A fascinating new study from Sweden suggests that repeated exposure to HIV via oral sex may trigger neutralizing antibodies that protect against the virus.
Some HIV-negative men in long term relationships with HIV-positive men have an antibody response in saliva which may inhibit HIV infection, report Swedish researchers in an article published online ahead of print in AIDS. This is the first time that such a response has been described in saliva, and may help explain why infection through oral sex is somewhat infrequently reported even in serodiscordant couples.

While it is well established that while HIV infection during fellatio and other types of oral sex can and does happen, the number of infections that can be attributed to oral sex is relatively small in comparison with the number of times that unprotected oral sex is practiced. One reason is that saliva contains enzymes which partially inhibit HIV infection.

Moreover, a number of studies, most famously among commercial sex workers in Kenya, have identified individuals who have had unprotected vaginal sex on many occasions and are likely to have been repeatedly exposed to HIV, but who have not been infected. It is thought that, through repeated exposure, these individuals have acquired a stronger immune response which makes HIV infection less likely. Different researchers have investigated a number of different markers of this immune response, including the presence of specific antibodies (IgA1) which may neutralise HIV, and HIV-specific CD4 cell responses.

Klara Hasselrot and colleagues from the Karolinska Institutet in Stockholm wished to investigate whether in long term relationships where one partner has HIV, the HIV-negative partner develops IgA1 antibodies in saliva that would help inhibit HIV infection during oral sex.

They recruited 25 HIV-negative men who were in a relationship of at least six months duration with an HIV-positive man. In addition, 22 HIV-negative men who were not in a serodiscordant relationship were recruited at a blood donor clinic to act as controls.

Klara Hasselrot told that the study participants’ questionnaires showed that 24 of the 25 men had performed unprotected receptive oral sex in the previous six months. For 21 men, this was with their HIV-positive partner, but for three men it was with casual partners of unknown HIV status. Just three men also reported unprotected receptive anal intercourse.

Moreover, analysis of the medical records of the HIV-positive partners showed that whilst most were on treatment at the time of the study, only two had been on antiretroviral treatment with undetectable viral loads for the entire length of their relationship. The researchers judge that this means that, with two exceptions, all HIV-negative partners have probably been exposed to HIV at some point.

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