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
via contaminated blood donations,
from infected mother to child [usually 30-40%],
via receptive anal intercourse with an infected male,
via contaminated intravenous injection equipment,
via receptive vaginal intercourse with an infected male, and
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.