WASHINGTON (AP) — A short time after it invades the body, the virus that causes AIDS creates a reservoir of silent infection that cannot be stamped out by current anti-viral drugs and may resist vaccines, a study shows.

The study, to be published Friday in the journal Science, sheds new light on how quickly HIV, the virus that causes AIDS, is able to establish a chronic, drug-resistant infection.

Earlier studies have shown that HIV establishes a reservoir of silent infection. The new research shows that this disease pool is created almost immediately after the virus is transmitted.

"These chronically infected cells are important because they allow the virus to persist below the radar screen of the immune system, particularly at the time of the transmission," said Dr. Ashley T. Haase, an HIV researcher at the University of Minnesota and the senior author of the study.

Haase said the study shows that a short time after the sexual transmission of the AIDS virus, there is an infection established in what are known as resting T-cells. These are white blood cells that are not actively participating in the body's immune response to the virus and are resistant to anti-viral drugs.

The finding is contrary to the belief that HIV first infects two other targets, macrophages and dendritic cells, and then spreads to active T-cells.

Instead, said Haase, the virus quickly moves in about equal proportions into both the resting and the active T-cells.

Dr. Tony Fauci, director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, said the Haase study "was a nice piece of work" that gives important new insight into the early stages of HIV infection.

By quickly infecting the resting T-cells, said Fauci, the virus "gives itself some insurance of survival." Virus in resting T-cells is a much more difficult target for both the immune system and for anti-viral drugs, he said.

Fauci said the finding also is "bad news for vaccines" because it makes it more difficult to inoculate the body against HIV infection.

In the study, Haase and his colleagues first studied the step-by-step progress of AIDS virus infection in monkeys. The animals were vaginally infected with SIV, the simian form of HIV. Researchers then took specimens to trace the disease progress.

They found that just three days after infection, the virus was in both activated and resting T-cells. In the following days, it spread faster and faster into the resting T-cells.

Haase said his group then looked at specimens from patients recently infected with HIV and found a similar pattern. The virus was present about equally in both resting and activated T-cells, he said.

Virus in the resting T-cells is reproducing at a very, very low level, said Haase. This makes the cells less obvious to the immune system. It also creates a powerful defense against anti-virals because these drugs attack HIV only when the virus is actively reproducing.

The finding suggests that the current drugs never will completely eradicate the virus, he said.

Haase said it is believed that the resting T-cells can persist in the body for years, perhaps decades. This means that the HIV in these cells would remain a threat even though the drugs reduce virus in the blood stream to an undetectable level.

Copyright 1999 The Associated Press. All rights reserved.