New research reveals that natural selection may be making HIV more transmissible in the United States.
By Desirée Guerrero
When HIV is transmitted in large population groups in the US, it is more likely to cause high viral loads. A recent study published in Nature Communications, led by Dr. Joel Wertheim of the University of California, San Diego, and Dr. Walid Heneine of the Centers for Disease Control and Prevention (CDC), led researchers to conclude that natural selection is causing it to become more transmissible and aggressive in certain groups.
Previously, researchers had theorized that HIV transmission was greater during primary infection, which would favor the selection of HIV variants that produce higher viral loads—the point where the viral load stabilizes after peaking during initial transmission. Without early diagnosis and immediate antiretroviral therapy (ART), the selection of these variants would lead to a shorter asymptomatic period and faster, more widespread transmission.
Early diagnosis and linkage to treatment can rapidly suppress viral loads; however, sexual networks where more frequent transmission can occur tend to counteract the effects of ART. Researchers say the only way to combat such effects in these groups would be through very early diagnosis (within the first few weeks of HIV infection) and the ability to trace and test the exposed sexual partners of someone experiencing this type of acute HIV infection.
Using a large database of HIV isolates, the research team assessed whether certain HIV variants were becoming more infectious and causing higher viral loads. They analyzed a total of 33,285 HIV samples from individuals registered in the National HIV Surveillance System database.
None of the samples, recorded in the database after genotypic testing for HIV drug resistance, showed signs of drug resistance mutations. Seventy-two percent had a viral load measurement recorded within three months before or one month after the sample was taken for genotyping. Interestingly, the researchers found that 37.5 percent of those with viral load results could also be genetically linked to another individual who had been sampled.
After carefully examining the genetic characteristics of the viruses, the researchers were able to identify closely related viruses that formed a total of 4,366 groups of people.
Those who were in groups generally had higher viral loads than those who did not acquire HIV in groups when diagnosed after the early infection stage (the first six months after HIV acquisition). The findings also revealed that group size appeared to affect viral loads: people in groups of ten or more had higher viral loads than those in smaller groups.
The study examined the viral loads of those sampled over a ten-year period. Researchers found that viral loads increased during that time by 0.2 log10 copies/ml in people diagnosed with a CD4 count above 500 cells, although similar patterns were observed for those diagnosed with lower CD4 cell counts. The researchers also found that people were more likely to be part of a transmission cluster in the later years of the decade: the more connections they had within a specific cluster, the higher their viral load was at the time of diagnosis.
These findings support previous research presented at the Conference on Retroviruses and Opportunistic Infections (CROI) in 2018 by some of the researchers in this study, when they discovered that rapidly growing transmission clusters in the U.S. involve young Latino/Hispanic men who have sex with men.
The authors of the study concluded that public health interventions based on molecular epidemiology (which identifies clusters of infections through matching viral genotypes in newly diagnosed individuals) would be highly beneficial in combating this type of natural selection in terms of transmission of these more virulent HIV strains.
From: https://www.hivplusmag.com/treatment/2020/1/14/hiv-evolving-be-more-aggressive-clusters