HOLLAND: The virus which causes Aids may be weakening over time as it spreads from person to person, according to new Dutch research. A small preliminary study indicates the HIV virus was far more infectious and virulent in the late 1980s than it is today.
A team from the Institute of Tropical Medicine in Antwerp compared samples of HIV-1, the most common cause of Aids, recovered from 1986-89 with isolates from 2002-03.
They found that the newer HIV-1 samples did not multiply as well and were more sensitive to drugs than the older virus samples.
Dr Kevin K Ariens and colleagues say they were working from a very small sample size, about 12 matched pairs of viral isolates. They also warn that this did not mean that efforts to halt the spread of HIV should be reduced.
The results clearly showed however that viral "fitness" had diminished over the 15 years from the late 1980s to today, the authors state.
The tendency of a highly virulent virus to weaken or "attenuate" over time was a well recognised phenomenon, according to the head of the virus research group within Trinity College's Moyle Institute, Prof Greg Atkins.
"The classic study of this was myxomatosis in rabbits," he said yesterday. The disease was highly virulent when it emerged from Brazil before spreading to Europe and Australia. "Now it has largely lost its virulence," he added.
"It happens with some viruses like the 1918 Spanish flu virus which is certainly less virulent. There is a selection pressure on the virus to do that. If it kills all its hosts it won't survive itself."
The research team used recognised HIV transmission models involving human immunological cells, allowing the older and newer HIV-1 samples to "compete" for survival.
"Overall the historical HIV-1 outcompeted the recent HIV-1 isolates in 176 of 238 competitions and in nine of 12 competitions," the authors report in the journal AIDS, official journal of the International AIDS society.
"The mechanisms responsible for a possible HIV-1 attenuation are complex and multifaceted but likely to involve directional evolution towards increased survival and transmission at the cost of lowering virulence," Dr Arien said.
The trade-off between lower virulence as a way to improve survival was a slow process, Prof Atkins said.
"It takes some time and it is certainly something the Aids virus would try to do over time," Prof Atkins added.
"What appears to be happening is that by the time HIV passes from one person to another, it has already toned down some of its most pathogenic effects in response to its host's immune system," said Keith Alcorn , senior editor at the HIV information charity NAM.
"So the virus that is passed on is less fit each time. This would suggest that over several generations, HIV could become less harmful to its human hosts. However, we are still far from that point. HIV is still a life-threatening infection."