Hopes of a total cure for HIV have been dealt a blow, after researchers in the US discovered that the reservoir of inactive viruses in a patient’s body may be up to 60 times larger than previously thought.

“Our study results certainly show that finding a cure for HIV disease is going to be much harder than we had thought and hoped for,” said senior investigator Dr Robert Siliciano, a professor at the Johns Hopkins University School of Medicine.

In a new study from Howard Hughes Medical Institute (HHMI) in Maryland, researchers discovered that the reservoir of latent or inactive HIV that lingers in a patient’s body is much larger than scientists believed.

“We’re working very hard on developing better ways to assess the size of this reservoir,” Dr Siliciano said. “But I think there’s a lot more we really need to understand before we do a lot more clinical trials.”

He added: “It doesn’t mean that it’s hopeless, but it does mean we need to focus on getting an even clearer scope of the problem.”

In HIV positive patients the virus targets the immune system’s T cells, and becomes integrated into the cell’s genes, making the cell reproduce the virus. Antiretroviral drugs target these active forms of the virus, but in some cells, the virus remains inactive. It is this type of virus that researchers now believe is far more numerous than previously thought.

Currently, researchers have no way of eradicating inactive HIV viruses.

Terrence Higgins Trust (THT), the UK’s largest sexual health and HIV charity, stressed the research highlighted the importance of HIV prevention.

THT Policy Director Lisa Power said: “Prevention is not only better than cure; it’s also the only viable option we have for the foreseeable future.

“This study shows just one of the challenges researchers need to overcome. What is alarming is how many people believe a cure already exists. It doesn’t, and false hope may be leading people to take risks.

“Until a cure is found, we have to throw everything we’ve got behind HIV prevention. Using condoms, testing for HIV and getting treatment are our best weapons against the virus.”

Figures released this month showed that a record number of gay and bisexual men were diagnosed with HIV last year in Australia.

In July, the UK’s Department of Health said it was “concerned” by rising HIV infections among gay and bisexual men living in London.