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Seminal HIV Load Linked to Higher Transmission Risk in MSM
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2nd International Workshop on HIV Transmission
August 26-28, 2007
Washington, DC
Mark Mascolini
A cross-sectional study of HIV-discordant gay men found that higher seminal HIV load, as well as higher blood plasma load, raised the risk of transmitting HIV to a sex partner [1]. Partner discordance for herpes simplex virus type 2 (HSV-2) infection also boosted HIV transmission risk.
Several earlier studies showed that a higher blood viral load in sex partners or pregnant women made HIV transmission to uninfected partners or newborns more likely. Blood plasma load correlates with HIV load in semen, but that correlation is weak [2]. Because data on seminal load and transmission risk are scanty, University of California, San Diego (UCSD) researchers measured blood and seminal loads in recently infected partners of 50 couples. Phylogenetic analysis showed that 17 newly infected men picked up HIV from their partner and 33 did not.
David Butler and coworkers reported that transmitting and nontransmitting couples did not differ significantly in mean age of source partners (33 and 31 years) or sexually exposed partners (32 and 34 years), or in median CD4 count (438 and 612 cells). Equivalent proportions of transmitting and nontransmitting source partners had recently become infected, and equivalent proportions were taking antiretrovirals.
Transmitting pairs proved significantly more likely than nontransmitting pairs to be serodiscordant for HSV-2 (50% versus 11%, P < 0.01) and significantly more likely to have an HSV-2-infected source partner and an HSV-2-uninfected recipient partner (37.5% versus 3.6%, P < 0.01).
Median seminal viral load was significantly higher in transmitters than in nontransmitters (3.63 versus 2.56 log copies/mL, P < 0.02). But the range of seminal loads in transmitters lay entirely within the range for nontransmitters, so seminal HIV was not a good predictor of transmission in this cohort. Median blood viral load was also significantly higher in transmitters than in nontransmitters (4.78 versus 4.06 log copies/mL, P < 0.01), and in this case the ranges did not completely overlap. Seminal load correlated with blood load in transmitters (higher blood load meant higher seminal load, R2 = 0.23), but the correlation proved stronger in nontransmitters (R2 = 0.51).
The UCSD team cautioned that, because seminal plasma load reflects only cell-free virus in semen, cell-associated load in genital secretions remains to be quantified, and its relation to blood viral load, seminal load, and transmission remains to be defined.
References
1. Butler D, Smith D, Cachay E, et al. Relationship between concentration of virus in seminal fluid and sexual transmission of HIV. 2nd International Workshop on HIV Transmission. August 26-28, 2007. Washington, DC. Abstract 51.
2. Vernazza PL, Dyer JR, Fiscus SA, et al. HIV-1 viral load in blood, semen and saliva. AIDS. 1997;11:1058-1059.
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