The charts/figures would not display. Would you please resend this article to this address and also to [log in to unmask] Charles --- "Edward E. Rylander, M.D." <[log in to unmask]> wrote: > > Table of Contents > > HIV Transmission > Intervention Strategies > Biological HIV Prevention Strategies: Reducing > Infectiousness, > Susceptibility, and the Efficiency of Transmission > Antiretroviral Therapy and HIV Transmission > Conclusion > References > Appendix: Talking About Safer Sex With Your Patients > _____ > > > HIV Transmission > > > Epidemiology of HIV Transmission > > HIV is spread from human to human by 3 routes[1]: > * blood transmission (contaminated > transfusions, needle sharing during drug > use, needle-stick injuries) > * vertical transmission (mother to offspring > during parturition or > breastfeeding) > * sexual transmission > Sexual transmission of HIV accounts for more than > 75% of infections > worldwide. > The probability of transmission of HIV by different > sexual routes per > episode of intercourse is summarized in Figure 1, > using data generated by > epidemiologists and mathematical modeling.[1] > Transmission of HIV from men > to their partners is more efficient than from women > to men.[2,3] > Transmission of HIV through anal intercourse is more > efficient than other > sexual behaviors. In addition, transmission per > episode of intercourse may > well be affected by the stage of disease of the > infected subject or innate > or acquired immunity of the exposed person as > discussed below. Oral sex > between women (cunnilingus) appears to confer almost > no risk, and fellatio > appears to have limited risk relative to sexual > intercourse. However, HIV > acquisition among gay men has been reported as a > result of fellatio > alone.[4] Among 122 individuals with primary HIV > infection, Dillon and > coworkers[5] attributed 6.6% of cases to oral sex. > In addition, simian > immunodeficiency virus (SIV) has been transmitted to > macaques through oral > inoculation using similar concentrations of virus as > those required for > vaginal infection.[6,7] > > Figure 1. Per-contact probability of HIV > transmission. The infectivity > ranges for sexual contact are derived from a > comprehensive review of the > literature (lower and upper bounds are from modeling > per-contact > transmission in different study populations with > different modeling > techniques). Each infectivity estimate for the other > routes of infection > originates from one representative study. The routes > of infection are as > follows: sexual intercourse, with indicating > female-to-male transmission, > indicating male-to-female transmission, and > indicating male-to-male > transmission; needle stick; needle sharing; > transmission from mother to > infant with and without perinatal zidovudine > treatment; and transfusion. > Royce RA, Sena A, Cates W Jr, Cohen MS. Current > concepts: sexual > transmission of HIV. N Engl J Med. > 1997;336:1072-1078. Copyright 1997. > Massachusetts Medical Society. All rights reserved. > The spread of HIV can be assessed at a population > level as well. Anderson > and May[8] have described the risk of secondary > (new) cases of HIV as Ro, > where Ro = beta x C x delta, with beta representing > the efficiency of > transmission, C the number of sexual partners, and > delta the duration of > infectiousness of the index case. When Ro exceeds 1, > new, secondary cases of > HIV occur, and the epidemic continues. Successful > prevention strategies must > reduce Ro to less than 1 and include lowering the > rate of partner change, > reducing the efficiency of transmission, and > shortening the duration of > infectiousness. This model offers an excellent > conceptual framework to > approach HIV prevention and a tool to examine the > success of interventions. > > Biology of HIV Transmission > > The efficiency of transmission of HIV represents a > biological event; > transmission either does or does not occur. HIV > transmission must depend on > the infectiousness of the index case (reviewed in > the paper by Vernazza and > coworkers[9]) and the susceptibility of the exposed > host (reviewed in the > paper by Buchacz and colleagues[10]). A schematic > representing the > transmission of HIV from a male to a female partner > is provided in Figure 2. > > Figure 2. Male-to-female transmission of HIV. > Infectiousness of HIV. HIV can be recovered from > seminal cells (CD4+ > macrophages and lymphocytes) and seminal plasma. > Detection of HIV in seminal > plasma by RNA polymerase chain reaction > amplification techniques has been > used as a surrogate for the concentration of HIV in > semen, although > procedures to eliminate inhibition of amplification > must be used.[11] When > the concentration of HIV in seminal plasma exceeds > 10,000 copies/mL, HIV can > usually be grown in seminal cells.[12] However, it > is unclear whether HIV is > transmitted from seminal cells or seminal plasma; > cell-free virions in > seminal plasma may be defective (and unfit). > The recovery of HIV from cervical mucus and > cervicovaginal lavage fluid is > similar to semen, although it has only recently been > possible to quantify > the copy number.[13,14] HIV can be recovered from > cervicovaginal lavage > fluid cells when the concentration exceeds 10,000 > copies/mL.[15] > Several lines of evidence suggest that the > concentration of HIV in genital > secretions can be correlated with risk of sexual > transmission. First, there > is overwhelming evidence that the concentration of > HIV in an infected > mother's blood determines the risk of vertical > transmission,[16-18] although > one must realize that the biologic mechanisms of > vertical and sexual > transmission are different. Second, a correlation > has been demonstrated > between increased concentrations of HIV in blood and > enhanced transmission > by all routes.[18-21] In a remarkable study in > Uganda, Quinn and > coworkers[22] demonstrated that HIV transmission in > HIV serodiscordant > couples could be correlated directly with the blood > plasma HIV RNA level in > the infected subject. No HIV transmission was > observed when blood plasma HIV > was less than 1500 copies/mL. In a similar study > among serodiscordant > couples in Rakai, Uganda, Gray and colleagues[23] > calculated that when the > blood plasma viral load was less than 3500 > copies/mL, the transmission > probability was 0.0001 (1 per 10,000 episodes of > intercourse). When blood > viral burden was greater than 50,000 copies/mL, the > transmission probability > was calculated to be 0.0051 (5.1 per 1000 episodes > of intercourse). It > should be noted the concentration of HIV in blood > can be directly (but > imperfectly) correlated with the concentration of > HIV in semen[11,12,24] and > female genital secretions.[15] > Third, the concentration of HIV in genital tract > secretions from males and > females is increased at times when enhanced > transmission is suspected, such > as in primary infection or in later stages of HIV > disease,[11,12,15,24,25] > and in patients with classic sexually transmitted > diseases (STDs) (reviewed > in the paper by Fleming and Wasserheit[26]). > However, recent data suggest > that the concentration of HIV in semen during > primary infection may not be > === message truncated === __________________________________________________ Do You Yahoo!? Get personalized email addresses from Yahoo! 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