Estimating the contribution of the gut to plasma viral load in early SIV infection

BACKGROUND: There is significant debate about whether the gut plays a major role in viral replication and pathology in HIV infection. Here we aimed to estimate the contribution of the gut to the total virus observed in plasma, by comparing the frequency of different viral mutants in plasma and gut in SIV infection. RESULTS: We found that the maximum contribution of gut to plasma viral load estimated from rectal biopsy at day 28 post-infection had a median of 10%. The estimated values for individual animals ranged from nearly 100% to <3% in 4/14 animals. Importantly, these are maximum estimates, so that a value of 90%, for example, means that the real contribution may be anything between 0 and 90%, just not higher than 90%. We also studied the contribution of gut at the peak of plasma viral load (day 14). However, since there was very little escape in most animals at this time point, we could only estimate the maximal contribution of gut in 4 animals, in two of which it was <15%. CONCLUSIONS: The role of the gut in HIV is a controversial area, with many suggesting that it plays a dominant role in driving early infection. Our analysis suggests that, at least by day 28 post-infection, the gut is not contributing greatly to the plasma viral load.