In a step that could greatly enhance the prevention and treatment of AIDS, scientists have created a strain of the human AIDS virus able to infect and multiply in monkeys. This could be a step toward testing future vaccines in monkeys before trying them in people, according to a new study.

Till now, a major drawback in terms of research was the lack of a perfect tool to analyse the HIV infection, as researchers largely depended on findings from monkeys infected with SIV - simian immunodeficiency virus - which contains only about 50 per cent of the genetic code of HIV.

However, now a research team, led by Howard Hughes Medical Institute (HHMI) researcher Paul D Bieniasz of the Aaron Diamond AIDS Research Center has genetically tailored a new HIV strain to infect a species of rhesus monkeys.

This strain of HIV, the human immunodeficiency virus, was developed by altering a single gene in the human version to allow it to infect a type of monkey called a pig-tailed macaque, the researchers said on Monday.

The genetically engineered virus, once injected into this monkey, proliferates almost as much as it does in people, but the animal ultimately suppresses it and the virus does not make it sick, they said. The strain is called simian-tropic HIV-1, or stHIV-1.

Elaborating on the study of the new HIV strain in the online edition of the Proceedings of the National Academy of Sciences, Bieniasz and his colleagues say they have established that three antiviral drugs, combined in one daily pill, could thwart HIV infection in the monkeys.

According to the researchers, since "the lack of a primate model that utilises HIV-1 has been an impediment to research", the new model can be considered "a real step forward" in terms of HIV research, as it will work in a way similar to humans.

"If our research is taken further, we hope that one day perhaps in the not-too-distant future, we'll be able to make vaccines that are intended for use in humans and the very same product will be able to be tested in animals before human trials," Bieniasz told Reuters in a telephone interview.

The scientists said that in making the genetically engineered virus they removed the HIV version of a gene, known as vif, and inserted the SIV version. This gene acts to thwart proteins made by the monkey that that kill viruses.

Bieniasz said the scientists may need to make additional changes in the stHIV-1 to make it better for testing vaccines.

The genetically engineered virus infects the monkeys and during the early course of infection is a reasonably good mimic of what happens in HIV-infected people, Bieniasz said. But after initially spreading in the monkey's body, the animal succeeds in suppressing the virus - not completely clearing the virus but driving it to very low levels.

"The slight problem is the monkeys don't go on to develop AIDS, they don't get sick," Bieniasz said.