A new and more aggressive strain of HIV discovered in West Africa causes significantly faster progression to AIDS, researchers at Sweden's Lund University have found.

The strain, called A3/02, was discovered in 2011 and is part of ongoing HIV/AIDS research.

So far, it has only been identified in the West African country of Guinea-Bissau and forms when two of the most common strains in the region fuse together.

The good news is that as far as we know the medicines that are available today are equally functional on all different subtypes of variants. Angelica Palm, Lund University

"Individuals who are infected with the new recombinant form develop AIDS within five years," Angelica Palm, one of the scientists involved in the study, said on Thursday.

"That's about two to two-and-a-half years faster than one of the parent [strains].

Research shows that recombinant strains, those created when different DNA combines, are a cause for concern.

"There have been some studies that indicate that whenever there is a so-called recombinant, it seems to be more competent or aggressive than the parental strains," Palm said.

There are two main types of the HIV virus: HIV-1 and HIV-2 with HIV-1 being the most common. But within those two categories, there are numerous subtypes.

The HIV virus can even mutate inside an infected person, according to the World Health Organisation.

But the scientists reassured patients that existing drugs will still effectively treat the new strain regardless of the speed at which it develops into AIDS.

"The good news is that as far as we know the medicines that are available today are equally functional on all different subtypes of variants," Palm said.

Other strains

A person goes from having HIV to AIDS when his or her white CD4 cell count, a white bloodcell that helps fight infection, drops below 200, according to the Mayo Clinic.

An estimated 35.5 million people around the world live with HIV, a virus that destroys the immune system and often leads to complications like pneumonia, tuberculosis,diarrhoea and tumours, according to the WHO.

But while the study only found the new strain in West Africa, scientists warn that other rapidly developing strains probably exist in regions like Europe and the US, where there are high levels of immigration.

"It is highly likely that there are a large number of circulating recombinants of which we know little or nothing," Patrik Medstrand, professor of clinical virology at Lund University, said.