New research from Lund University in Sweden suggests that a new aggressive strain of HIV develops more rapidly into AIDS than other current strains.
The new strain is a "recombinant" virus - a cross of two viruses that meet in an infected person.
The two viruses, known as 02AG and A3, are the two most common strains in Guinea-Bissau, West Africa. The recombinant strain is called A3/02 and so far has only been seen in the region.
There are over 60 different epidemic strains of HIV-1 in the world. But usually different regions are dominated by only one or two of them.
However, if two strains infect the same person, they can combine to form a cross between the two - known as a recombinant.
The researchers report their findings in the Journal of Infectious Diseases, and first author Angelica Palm, who is working toward a doctorate at Lund, says:
"Recombinants seem to be more vigorous and more aggressive than the strains from which they developed."
The new strain, A3/02, has previously been described by one of the other authors, Dr. Joakim Esbjörnsson.
Recombinant strains of HIV are spreading rapidly around the world
Although it has so far only been seen in West Africa, other studies have shown recombinants are spreading more rapidly around the world.
Parts of the world, such as the US and Europe where there are high levels of immigration, are seeing increasingly mixed and complex variants of HIV. This is quite different to the early years of the HIV epidemic, when there were few dominant strains and no recombinants.
The researchers suggest we need to be wary of the rise in recombinants, as senior author Patrik Medstrand, professor of Clinical Virology at Lund University, explains:
"HIV is an extremely dynamic and variable virus. New subtypes and recombinant forms of HIV-1 have been introduced to our part of the world, and it is highly likely that there are a large number of circulating recombinants of which we know little or nothing. We therefore need to be aware of how the HIV-1 epidemic changes over time."
The researchers drew their conclusions after looking at data gleaned in a Lund University project that carried out a long-term follow-up of HIV-infected people in Guinea-Bissau.
The team is now planning to spend more time looking at recombinant viruses and their occurrence among HIV-infected people in Europe.
In 2012, scientists at the University of California, Los Angeles (UCLA), reported finding a clue as to why some people infected with HIV appear to remain healthy for 20 years or more, while others progress to AIDS much faster.
They found that "slow progressors" were more likely to carry a gene variant that causes the immune system to attack a particular section of the HIV protein.