The Aids virus HIV can keep on growing even when it is undetectable in the blood of treated patients, new research has shown.

As a result, the virus rapidly bounces back if a patient stops taking the anti-retroviral drugs that keep the infection in check.

Scientists discovered that a viral reservoir in the lymphatic system was continually being replenished in patients, despite their blood tests showing up negative.

The study underlines the importance of delivering high concentrations of anti-retroviral drugs to all the parts of the body where HIV can grow.

Steven Wolinsky, one of the researchers from Northwestern University in the US, said: “We now have a path to a cure.

“The challenge is to deliver drugs at clinically effective concentrations to where the virus continues to replicate within the patient.”

Co-author Angela McLean, professor from Oxford University, said: “The study is exciting because it really changes how we think about what is happening in treated patients.

“It helps explain why some strategies that tried to clear the reservoir have failed.”