Scientists have made a breakthrough in understanding how HIV spreads through the human body after filming the process for the first time ever.
Researchers found that the virus is transferred from infected cells to healthy ones in a previously unknown way.
It is hoped that the discovery will help researchers create a vaccine to combat the virus, which has led to the deaths of more than 25 million people.
Video Refered by Eddie Salinas
The study was made possible after experts created a molecular clone of infectious HIV and inserted a protein into its genetic code which glows green when exposed to blue light.
This allowed scientists to see the cells on digital video, and capture the way HIV-infected T-cells interact with uninfected ones.
They noted that when an infected cell came into contact with a healthy one, a bridge was created between them, called a virological synapse.
Researchers were then able to observe the fluorescent green viral particles moving towards the synapse and into the healthy cell.
The US study has broken new ground by revealing that it is the synapse through which the viral proteins are gathered and moved into uninfected cells.
The team, comprising scientists from UC Davis university in California, and Mount Sinai School of Medicine in New York, believe that this knowledge could help create new treatments for HIV and Aids.
Study author Dr Thomas Huser, chief scientist at the UC Davis Center for Biophotonics Science and Technology, said: "Our findings may explain why attempts to develop an HIV vaccine have so far been unsuccessful.
"The more we know about this mode of transfer, the better chance we have of figuring out how to block it and the spread of HIV and Aids."
For decades it was believed that HIV was mostly spread around the body through freely circulating particles, which attach themselves to a cell, take over its replication machinery and make multiple copies of themselves.
In 2004, scientists discovered that cell-to-cell transfer of HIV also occurred via virological synapses, but it was not understood why the process was so effective in spreading the virus.
Due to this, previous efforts to create an HIV vaccine have focused on priming the immune system to recognise and attack proteins of free-circulating virus.
The new video footage indicates that HIV avoids recognition by being directly transferred between cells.
Dr Huser said: "We should be developing vaccines that help the immune system recognise proteins involved in virological synapse formation and antiviral drugs that target the factors required for synapse formation."
Co-author Benjamin Chen, assistant professor of medicine and infectious diseases at the Mount Sinai School of Medicine, added: "Direct T-cell-to-T-cell transfer through a virological synapse is a highly efficient avenue of HIV infection, and it could be the predominant mode of dissemination."
Further research intends to discover what happens to viral particles once they are transferred into a newly infected cell.
The study's finding are published in the journal Science.