Giving a patient HIV drugs as soon as they are diagnosed could be the future of treatment, say researchers.

Currently, antiretroviral therapy is given only once the immune system has been seriously weakened by infection.

A trial, in the New England Journal of Medicine, showed that a year-long course of therapy after diagnosis helped preserve the immune system and keep the virus in check.

It is thought that early treatment may also reduce the spread of HIV.

The virus is no longer a death sentence for patients who get the best care and drugs. Treatment is given once their CD4 T-cell count, a part of the immune system, falls below 350 cells per cubic millimetre of blood.

However, there has been some speculation that starting as soon as a patient is diagnosed may be more beneficial.

The Spartac study, which involved 366 patients from eight countries around the world, tested the theory.

Some patients were given 12 weeks of drugs after being diagnosed, another group had drugs for 48 weeks after diagnosis and a third group were given no drugs until they reached the 350 level.

Prof Jonathan Weber, from Imperial College London, said those on the 48-week regime "end up with much higher CD4 cell count and a much lower viral load".

"Also, the benefit persists after you've stopped treatment," he added. Who pays?

Keeping a strong immune system is important for preventing other "opportunistic" infections, such as tuberculosis, taking hold.

Prof Weber acknowledged that cost was a "massive question" that would represent "a real problem" in poorer parts of the world.

However, in richer countries if would mean "only a few extra years" on a lifetime of medication.

Dr Sarah Fidler, also from Imperial, pointed to the benefit of keeping levels of the virus low.

"This could be very important for helping reduce the risk of passing on the virus to a sexual partner," she said.

Dr Jimmy Whitworth, from the Wellcome Trust, which funded the study, said: "This study adds to increasing evidence that early initiation of HIV treatment is of benefit to the individual in preventing severe disease and in reducing infectiousness to his or her partners.

"Questions remain about whether a longer course at an early stage could be more beneficial or whether early treatment should be continued for life."

However, one of the biggest problems remains identifying people who have been infected. In the UK, one in four people with HIV are thought to be completely unaware they have the infection.