The amount of HIV in the blood is directly related to the amount of virus shed in the vagina, according to a study of 97 HIV-infected US women published in the August 15th edition of the Journal of Acquired Immune Deficiency Syndromes. The finding could have important implications for the transmission of HIV, both mother to infant and between sexual partners, say the researchers.
The extent to which the virus can be detected in the genital tract of HIV infected woman has varied according to different reports, from nine percent of cases up to 80%. But this new study is different in that it has tracked the amount of virus secreted genitally in women before they started potent HIV therapy and regularly for almost three years after. The levels were then compared with blood levels of the virus measured at the same time.
Women had a pelvic examination and blood and cervicovaginal samples taken at the start of the study and then at two weeks, one month and every six months after.
The genital tract samples were taken using a technique called cervicovaginal lavage fluid collection. This involved gently rotating a swab against the wall of the cervix then washing the swab in a fixed amount of fluid which was then tested for virus.
The researchers also looked for the presence of other genital infections such as bacterial vaginosis, candidiasis (thrush) and trichomoniasis as well as the presence of semen to see whether any of these were associated with the levels of HIV in the genital tract. But they found that the only factor that affected the levels of HIV shed in the vagina was the amount of virus in the blood.
In fact, the blood HIV levels could be directly linked to the amount of virus shed. Women who had detectable blood levels were almost 14 times more likely to have virus in the genital tract than women who had undetectable blood levels. As the blood virus levels rose and fell, so did the levels in the genital tract. The researchers also discovered that virus levels in the genital tract seem to lag slightly behind those in the blood. When women achieved undetectable virus levels in both the blood and vagina, rebound of virus occurred in the blood first or at about the same time.
The researchers say these findings have important implications for transmission of HIV between sexual partners and from mothers to babies. It also substantiates previous research which has suggested that blood virus levels are the key factor in transmission risk.
In fact, they conclude, it is plausible to suggest that women with undetectable blood HIV levels are much less likely to shed virus genitally and therefore transmit the infection.
But they emphasise that even these latest data contain suggestions the picture might not be so clear. On five per cent of occasions there seemed to be greater levels of virus in the vagina than in the blood.
Limitations with the study are acknowledged by the investigators. Since it was carried out a more accurate way of measuring HIV levels in the vagina has been developed. Also genital HIV shedding is intermittent and measurements taken more often might have revealed a different pattern.
Cu-Uvin S et al. Association between paired plasma and cervicovaginal lavage fluid HIV-1 RNA levels during 30 months. Journal of Acquired Immune Deficiency Syndrome 2006; 42(5): 584-587.