Viral load in rectal secretions

There has been scant study into the relationship between viral load in the blood and that of rectal secretions , although limited data suggest that HIV may be higher in rectal secretions than either blood or semen, and can still be shed in the rectum despite successful antiretroviral therapy.

A study from the United States¹ of the effect of early HAART 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 loads below 50 copies/ml had detectable virus (as measured by RNA) in rectal secretions.  However, HIV DNA was more commonly detectable in the rectum (28% of men with plasma viral load below 50 copies/ml).

The largest study so far, in 64 gay men in the US and Peru,² also took place during the early HAART era. Twenty-seven (42%) of the men had been on a stable antiretroviral regimen for at least 30 days, and the remainder were drug-naive. This study compared levels of viral load in the blood, semen and the mucosal lining of the rectum and 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.

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 found that one-log₁₀ reduction in blood viral load caused a 0.5-log₁₀ reduction in both rectal and seminal viral load.