Are gut imbalances a risk factor for HIV infection?

For scientists, an “association” is where two phenomena occur at the same time, without necessarily having a cause-and-effect relationship. Is the gut dysbiosis (i.e. imbalance of the gut flora’s composition) observed in those infected with human immunodeficiency virus (HIV) a cause or a consequence of the disease? Or is it both? With only a few days to go before World AIDS Day on December 1st, the jury is still out, since the state of the gut microbiota prior to infection is not well known, and many other factors influence the appearance of dysbiosis, including age, diet, antibiotic use, and even sexual behavior, according to some recent data^2,3.  

To get a clearer picture, US researchers brought together gut microbiota samples from about 50 men who have sex with men, collected during different studies. They selected individuals with similar profiles (age, ethnicity, sexual behavior, etc.), half of whom were infected with HIV during the course of the studies, with the other half remaining HIV free. They were thus able to compare the gut microbiota of the infected men before and immediately after infection, and to compare the infected men’s gut microbiota with that of the healthy uninfected pairs.

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Minimal changes in microbiota before/after HIV infection... 

The authors first found that the composition of the infected men’s gut microbiota changed very little during the acute phase of HIV. Only increased Fusobacterium mortiferum was observed. Not normally resident in the gut flora, this bacterial species had already been associated with HIV in other studies.

... but significant pre-infection differences vs. controls

In contrast, the gut microbiota of the men who would go on to be infected with HIV (i.e., their “pre-infection” gut microbiota) differed from that of the controls (who remained HIV free). In particular, they had fewer bacteria from the Bacteroides group, and increased levels of Megasphaera elsdenii, Acidaminococcus fermentans, and Helicobacter cinaedi. This type of dysbiosis has frequently been observed in HIV-infected individuals. However, in this new study, the gut imbalance appears to have been present before infection, potentially influencing susceptibility to HIV, according to the authors.

Gut microbiota, a new tool for preventing HIV?

So, does gut microbiota composition play a role in susceptibility to HIV infection? Encouraged by similar conclusions from another US team⁵, the researchers propose that this avenue be followed up by studies on larger samples. They hope that this will identify a “gut microbiota signature” associated with greater susceptibility to HIV infection, thus allowing more targeted prevention via treatment of the gut microbiota of people at risk.⁶  

The researchers make it clear that this finding does not contradict the idea that HIV can itself cause dysbiosis. The short duration of the study meant it was not possible to observe the changes in gut microbiota composition that occur during chronic HIV. In addition, these results were obtained in a small group with a specific profile and thus generalizability beyond this population is limited.