Viral load in rectal secretions

  • Few studies have examined the relationship between viral load in the blood and rectal secretions.
  • An early study suggested that viral load may be higher in rectal secretions than in the blood.
  • However, a more recent study suggests that this is not the case, and that STIs do not appear to increase rectal viral load when blood viral load is undetectable.

There has been scant study into the relationship between viral load in the blood and that of rectal secretions. Although earlier limited data suggested that HIV may be higher in rectal secretions than in either blood or semen, and could still be shed in the rectum despite successful antiretroviral therapy, more recent data have put this into question. A 2011 American study suggests that not only are viral loads in the blood and rectal secretions highly correlated, but the presence of sexually transmitted infections does not seem to increase rectal viral load when blood viral load is undetectable.

Kelley and colleagues measured blood plasma and rectal viral load in 80 HIV-positive men using samples collected via swabs used to monitor infection with gonorrhoea or chlamydia.1 A total of 59 men (74%) were taking antiretroviral therapy, of whom 63% had a blood plasma viral load below 1000 copies/ml and 47% had a blood plasma viral load below 50 copies/ml. Almost all of the men (95%) had rectal human papillomavirus (HPV) infection, and two-thirds had herpes simplex virus. Rectal gonorrhoea or chlamydia were detected in 39% of men.

Detectable rectal viral load was found in 38% of men, overall. Viral load in rectal samples and blood plasma were highly correlated. This included men with rectal sexually transmitted infections. The only factor associated with an increased risk of having detectable virus in the rectum was a plasma viral load above 1000 copies/ml (p = 0.008).

An earlier study from the United States of the effect of treatment on viral load in the rectal mucosa of 233 gay men in Seattle found that just one man out of the 54 (2%) with blood plasma viral load below 50 copies/ml had detectable virus (as measured by RNA) in rectal secretions.2

The most commonly cited study on the relationship between viral load in the blood and rectal secretions found that although blood plasma viral load correlated with those in the semen and rectum, viral loads tended to be higher in rectal mucosa secretions than those in blood and semen.

However, this study of 64 gay men in the US and Peru took place during the early HAART (highly active antiretroviral therapy) era with only 27 (42%) of the men on a stable antiretroviral regimen for at least 30 days. In the men on antiretroviral therapy, when viral loads were an average of 200 copies/ml in blood, they were 1000 copies/ml in semen and 3980 copies/ml in rectal secretions. Using mathematical modelling, the investigators estimated that a one-log10 reduction in blood viral load caused a 0.5-log10 reduction in both rectal and seminal viral load.3

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References

  1. Kelley CF et al. HIV-1 RNA rectal shedding is reduced in men with low plasma HIV-1 RNA viral loads and is not enhanced by sexually transmitted infections in the rectum. J Infect Dis 204: 761-67, 2011
  2. Lampinen TM et al. Association of antiretroviral therapy with detection of HIV-1 RNA and DNA in the anorectal mucosa of homosexual men. AIDS 14: F69-F75, 2000
  3. Zuckerman RA et al. Higher concentrations of HIV RNA in rectal mucosa secretions than in blood and seminal plasma, among men who have sex with men, independent of antiretroviral therapy. J Infect Dis 189: 156-161, 2004
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