WASHINGTON, Nov 12 (AFP) - The virus that causes AIDS may be harder to eliminate than previously thought, according to a study published in Friday's edition of the journal Science.

Researchers have found that the AIDS virus can enter and survive inside inactive white blood cells, only to begin multiplying when the host cells become active at a later time, the study said.

Scientists had previously thought the human immunodeficiency virus, known as HIV, could only reproduce itself inside activated white cells, while inactive, or resting, white cells provided little opportunity for replicating and spreading of the virus.

But HIV stowed away inside resting white cells can survive current drug therapies aimed at destroying it and an immune system defense.

When the white blood cells encounter a foreign substance in the blood, usually a protein or protein fragment, they become activated and begin multiplying rapidly to fight the intruder.

And any HIV inside them, having seized control of the cells' reproductive machinery, multiplies itself, which leads to acquired immune deficiency syndrome (AIDS).

"We think chronically infected cells that produce only a little virus, as well as latently infected resting cells with silent infections, are difficult targets for the immune system or therapy," said Ashley Haase, a professor of microbiology at University of Minnesota and author of the study.

"These cells fly below the radar screen of the immune system. They also live a long time and won't be affected by our current combinations of anti-AIDS drugs that work by interfering with the chain of new infections that maintains virus production," Haase said.

Researchers confirmed their theory by testing HIV-infected people.

The study was carried out by researchers at several universities in the United States, including the University of Minnesota; Germany; and the Netherlands.

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