In a landmark finding researchers at the University of Alabama, Birmingham (UAB) have revealed that only a few HIV variants may lead to sexual transmission of the virus.
The team has come up with a mathematical model to identify precisely those viruses responsible for HIV transmission.
Previous studies had shown that the 'bottleneck' effect occurred when few versions of the virus led to infection while many variants are present in the blood.
Dr. George M. Shaw, professor in the UAB departments of Medicine and Microbiology and senior author on the report, said the research sheds new light on potential vulnerabilities in the virus at a time when science, medicine and society are still reeling from the failure of a major HIV vaccine clinical trial.
"We can now identify unambiguously those viruses that are responsible for sexual transmission of HIV-1. For the first time we can see clearly the face of the enemy," said Shaw, a project leader with the Centre for HIV/AIDS Vaccine Immunology.
The researchers sequenced many copies of the HIV envelope gene present in the viruses taken from 102 recently infected patients.
The envelope gene encodes for a protein called Env that forms part of the outer covering of the virus, and is responsible for its infectiousness.
They then used sophisticated mathematical models of HIV replication and genetic change to identify the virus or viruses responsible for transmission.
The findings revealed that in 80 percent of the newly infected patients, a single virus caused transmission, though each virus was different in each patient.
In the other 20 percent of patients, two to five unique viruses caused transmission.
"Previously, researchers employed inexact methodologies that prevented precise identification of the virus that initiated infection," said Brandon Keele, Ph.D., an instructor in UAB's Department of Medicine and lead study investigator.
"Our findings allow us to identify not only the transmitted virus, but also viruses that evolve from it," he added.
The team believes that their work would lead to new studies on how different HIV genes and proteins work together to make a virus biologically fit for transmission and for growth in the face of mounting immunity.
The findings are published online in the Proceedings of the National Academy of Sciences.