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Frerichs, R.R. Saliva and HIV Transmission.

SEA-AIDS Network, August 29, 1996

Posted in response to:

SEA-AIDS, August 27, 1996

From Project Team, Kunming, China

We have recently heard reports that HIV can be transmitted by saliva and therefore deep kissing. No-one has been able to reference or source these reports. However it is causing confusing messages and uncertainties.

Can someone please clarify this for us, sourcing references if possible?

Project Team

HIV/AIDS Red Cross Project Office - Kunming

Kunming, 650021, Yunnan, China.

R.R. Frerichs Posting

I am responding to the group from Yunnan who asked of reports that HIV can be transmitted by saliva. The worry that "deep kissing" (known as "French kissing" in the United States but likely by some other name in France) results in the exchange of saliva, and therefore may result in HIV transmission.

Most experts feel that saliva is an unlikely vehicle for HIV spread because the virus is uncommon in saliva, and when present, tends to be there at very low levels.

Furthermore, there appears to be a factor in saliva that inhibits viral transmission, making it even harder for the virus to move from one person to another. A good article on this topic appeared some years ago in the Journal of the American Dental Association (Barr, C.E. et al. Recovery of infectious HIV-1 from whole saliva. Journal of the American Dental Association 123(2)36-48, 1992.). They wrote in their abstract:

Whole saliva and serum samples were collected from 75 HIV- infected homosexual or bisexual men. Thirty-eight percent of cultured sera were positive for cell-free, infectious virus while only 1 percent of the 218 cultured whole salivas contained cell-free, infectious virus. These data support previous studies suggesting unlikely potential transmissibility of HIV infection by saliva.

The recent interest in this topic seems to have come from a June 7th Science article by Baba and colleagues (Science 2721486-9, 1996), who state in their abstract:

Unprotected receptive anal intercourse is a well-recognized risk factor for infection with human immunodeficiency virus-type 1 (HIV-1). Isolated human case reports have implicated HIV-1 transmission by oral-genital exposure. Adult macaques exposed nontraumatically to cell-free simian immunodeficiency virus (SIV) through the oral route became infected and developed acquired immunodeficiency syndrome (AIDS). The minimal virus dose needed to achieve systemic infection after oral exposure was 6000 times lower than the minimal dose required to achieve systemic infection after rectal exposure. Thus, unprotected receptive oral intercourse, even in the absence of mucosal lesions, should be added to the list of risk behaviors for HIV-1 transmission.

What was overlooked by many was that Baba et al were studying simian immunodeficiency virus, not human immunodeficiency virus, and that theirs was an artificial setting, and not an observation of normative human behavior.

Perhaps a rare case of HIV does occur by transmission via saliva, but likely it is very rare, and would warrant considerable media attention. Of course the most common modes of transmission are

  1. via contaminated blood donations,

  2. from infected mother to child [usually 30-40%],

  3. via receptive anal intercourse with an infected male,

  4. via contaminated intravenous injection equipment,

  5. via receptive vaginal intercourse with an infected male, and

  6. via insertive anal intercourse into an infected male or insertive vaginal intercourse into an infected female.

Adding sexually transmitted diseases to the equation enhances the risk of transmission, as does the presence of other factors, recently described by Stan Vermund ("Limitations in characterization of heterosexual HIV transmission risk: commentary on the models of Downs and de Vincenzi." Journal of Acquired Immune Deficiency Syndromes and Human Retrovirology 11(4)385-387, 1996).

Given these major modes of transmission and their well documented risk, the rare (if ever) transmission by saliva via deep kissing should be viewed as a curiosity, rather than a public health problem, at least until new data prove otherwise.