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Background:  Vasectomy does not affect the seminal shedding of HIV-1, suggesting that the distal male genitourinary (GU) tract is the major source of virus in semen. To investigate potential distal GU tract sources of HIV-1 we conducted extensive sampling of seropositive men who shed HIV-1 in their semen.

Methods:  Semen was collected 1 to 4 weeks prior to the sampling procedure. No subject had symptoms or signs of urethritis. The following samples were then obtained sequentially: blood plasma, urethral secretions (wick or swab), first-void urine, expressed prostatic secretions (EPS) and post-prostate massage urine (PMU). Subjects then had trans-rectal, ultrasound guided prostate biopsies obtained from six prostate areas (apex, middle and base, bilaterally). These biopsy specimens were evaluated for HIV RNA (right side) and DNA (left side) using polymerase chain reaction amplification methods.

Results:  We evaluated 15 HIV⁺ men  (median CD4⁺ cells 206/<GREEK>mu<GREEK>L, HIV-1 RNA 49,800 copies/mL; 5 on antiretroviral therapy). HIV RNA was detected in 32/34 semen specimens from the 15 men (median 38,400 copies/mL; range 72 to 1,720,00), in the urethral fluid (n = 10 tested: 15,400 copies/mL; 225 to 993,000), and EPS (n = 9: 7700 copies/mL; 4040 to 934,000). Following prostate massage, HIV RNA was higher in post-PMU (467 copies/mL; 28 to 68,600) compared to first-void urine (39 copies/mL; 17 to 848) (n = 11; p <0.02). HIV RNA was detected at >50 copies/mcg tissue RNA in 26/45 (58%) prostate biopsy specimens from 11/15 (73%) men (1,100 c/mcg; 59-165,000) and HIV DNA > 10 copies/<GREEK>mu<GREEK>g tissue DNA in 7/45 (16%) specimens from 5/15 (33%) men (299 copies/<GREEK>mu<GREEK>g; 86 to 3100). The 6 prostate areas sampled showed a similar distribution of HIV RNA and DNA. Three of 9 men (33%) with both EPS and urethral fluid specimens had no detectable HIV in their prostate tissue despite having detectable HIV RNA in their urethra fluid (mean 43,300 copies/mL), EPS (175,000 copies/mL) and post-PMU specimens (362 copies/mL of urine); the mean seminal and blood plasma HIV-1 RNA levels were 149,200 copies/mL and 31,000 copies/mL, respectively.

Conclusions:  The prostate and associated structures are likely significant sources of HIV. However, the low frequency of HIV RNA detected in prostate biopsy specimens, coupled with the high HIV levels in urethral fluid, EPS, and PMU suggests that distal lower GU tract structures, in addition to the prostate, are major sources of seminal HIV. These observations provide important insights into the pathogenesis of HIV-1 shedding in semen.

Keywords: Semen; Genital tract; Prostate