The Aids virus has been captured on film spreading for the first time in a huge breakthrough.
It sheds fresh light on how HIV - human immunodeficiency virus - infects cells during sexual intercourse.
The development could lead to better treatments for the disease that has already claimed the lives of 35 million people across the globe.
In the video the virus is illuminated with a fluorescent protein - making it appear as bright green dots.
The French team of scientists has already begun work on developing a vaccine based on these early steps of transmission.