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Do we already have a microbicide?
While breast-fed infants can clearly be infected with HIV by mouth, the mucosal surfaces in the mouth do not seem to allow adult human infection so readily. It has been argued that the rarity of transmission of HIV through oral sex may be due in part to substances in saliva, which inhibit the growth of HIV (Baron).
Another key observation is that the per-exposure risk of HIV infection through vaginal sexual contact is generally low. Important exceptions apply where STIs are present and possibly where girls are young and physically immature.
Natural human defences against HIV and other microbes, especially at mucosal surfaces, may therefore be important in preventing even more rapid HIV transmission. There is some evidence that these include local HIV-specific immune responses. In all microbicide research, it is necessary to be on guard against the possibility that a product will undermine natural protection - or the protection gained from future vaccines - and so make the situation worse, not better. This is an area where microbicide and vaccine researchers can work together and are increasingly likely to need to exchange ideas and experimental results (Kaul).
Sexual lubricants as microbicides
Researchers at the University of Texas set out to assess all vaginal lubricants sold commercially in the USA for their ability to inhibit the growth of HIV in cell cultures, in the presence of seminal fluid. They also looked at the ability of these mixtures to protect against cell-free HIV. After excluding products containing nonoxynol-9 (N-9), and others thought most likely to cause irritation, they reached the conclusion that three of the 22 commercial products they examined could, indeed, greatly inhibit HIV. Specifically, AstroGlide (made by Biofilm of Vista, California), Vagisil (Combe, White Plains, New York), and ViAmor (WomenFirst Healthcare Inc). They have not, however, shown activity against other viruses or sexually transmitted infections (Baron).
Unfortunately, this does not automatically mean that these products can or should be promoted for HIV prevention. Experience with N-9 has shown that laboratory studies can be misleading.
The Global Campaign for Microbicides has observed that these products have not been evaluated for their effect on vaginal or rectal mucosa, especially when used regularly in the quantities that might be needed for microbicidal use. Their US licensing is only as cosmetics, not as medicines, which requires a lower level of safety testing.
The only way to assess the value of these or other products would be through conducting clinical trials specifically designed to assess their safety and efficacy. If their manufacturers are able to sponsor such trials, this may yet happen. Otherwise, the current consensus is that there are more scientifically interesting and promising candidates which should be evaluated first.
Some have asked if the 'placebos' used in microbicide trials are themselves protective (for example, in the COL-1492 trial discussed under Nonoxynol-9 research, Replens was at least as effective as an N-9 formulation: did that mean N-9 was useless or that Replens was quite effective?). Others argue that such products are clearly of only marginal value for HIV prevention and it is reasonable to demand that any microbicide shows a substantial improvement over them (Stein).
Lemon juice as a microbicide
A Melbourne-based researcher, Professor Roger Short, has called for consideration of lemon juice as a possible anti-HIV microbicide. The basic principle, that acids - such as lemon juice - can inactivate both sperm and HIV, has been known for some years.
Current microbicide research does include products - BufferGel and Acidform -based on the principle of keeping the pH of the vagina low during sex, though the goal has been described as 'acidifying the semen, not acidifying the vagina'. BufferGel is set for full-scale international clinical trials sponsored by the US National Institutes of Health through its HIV Prevention Trials Network. However, a study which combined Acidform and N-9 found that the acid increased the damage done by N-9 to an unacceptable level.
There are many unanswered questions and the experience with N-9 has made microbicide researchers wary of premature adoption of untested products. With a natural but potentially dangerous product, what is the safety margin? How long would any effect last? Which method of applying the juice would be most effective with least risk of harm? What would be the effect on sexually transmitted infections and reproductive tract infections other than HIV?
References
Kaul R. Mucosal immunity and HIV-1 transmission. Microbicides 2002, Antwerp (www.itg.be/micro2002), 2002.
Stein Z et al. Appropriate controls in microbicide efficacy trials: the continuing search. XIV International AIDS Conference, Barcelona, abstract TuPeC4834, 2002.