BODY : FITNESS & EXERCISE VIRAL LOAD VALUABLE BAROMETER IN AIDS CASES.

Byline: Laura Beil Dallas Morning News

Some people infected with the AIDS virus spend a lot of time watching numbers rise and fall. A T-cell count, long viewed as the main measure of disease, is so important that a low number alone will cause an infection to be diagnosed as AIDS.

Recently, medical science has come up with perhaps an even more valuable barometer. Doctors can now use a new measurement called viral load. The difference is something like measuring a thunderstorm with either a rain gauge or color radar: A T-cell count can tell you how much it's raining, but viral load can discern how big the oncoming front is.

``It's probably going to become the most important tool clinicians will use,'' said Dr. Neil Graham of Johns Hopkins University in Baltimore, one of several researchers who presented viral load studies last month during the International Conference on AIDS in Vancouver, British Columbia.

Research discussed in Vancouver suggests that viral load can be a fairly precise predictor of the speed at which a person's health will decline in the coming years. Viral load measurements have also helped reveal what happens when the human immunodeficiency virus first invades the body.

``I think it's a substantial, if not major, advance,'' said Dr. Scott Hammer of Harvard Medical School in Boston. ``It has been a key to understanding the disease better.''

A T-cell count is a reflection of the immune system components, called CD4-T lymphocytes, that are destroyed when HIV replicates. A T-cell count of 200 means that a person has 200 cells per cubic millimeter of blood. The higher the number, the better.

Viral load, which is also referred to as viral burden, is like a census of the actual number of HIV copies inhabiting the body. It is a test for the virus's genetic material, RNA. In one common test, the number is written as the number of RNA copies per milliliter of blood. The higher the number, the worse the threat to a patient's health.

The most common way HIV was directly measured in the past was by removing a tissue sample and trying to grow the virus, Graham said, a tedious process that could take two weeks to produce results. Technological advances in the past few years, however, have led to tests that can provide an answer in a matter of hours with just a blood sample.

Scientists have wasted no time in putting viral load testing to use. Early last year, researchers from the University of Alabama at Birmingham and the Aaron Diamond AIDS Research Center in New York published separate reports in the scientific journal Nature that put the early stages of infection in a whole different light.

The early stages of infection used to be thought of as a quiet period, when HIV grew slowly, mustering troops for a full attack. That would have explained why a person can be infected for a decade without serious illness.

That idea first began to crumble in 1993, when researchers using a kind of home-brew viral load test published a report in the prestigious journal Science demonstrating that significant levels of HIV are present at all stages of disease.

When the results for that experiment first came in, ``it was one of those few moments in life you remember,'' said Dr. Michael Saag of the University of Alabama, a co-author of the Science paper. ``I looked at this data, and it was incredible.''

Then the two 1995 Nature reports drove the point home. Using easier-to-perform viral load tests and new, potent anti-AIDS drugs, the scientists learned that HIV actually is engaged in an all-out offensive during this time. Basically, the investigators first measured the viral load, then gave a patient the powerful drugs and tracked how quickly HIV declined.

The findings were dramatic, even though most AIDS experts already were skeptical of the latency idea. But the Alabama and New York scientists found that more than 2 billion copies of HIV are being churned out every day. After two weeks, an infection that is 99 percent wiped out can rebuild itself from the ruin.

``The virus is not just sitting there minding its own business in the early stage of disease,'' Graham said.

When a person is first infected, however, the immune system is able to keep up with the viral replication, like a two-horse race with the competitors neck and neck. But the struggle goes on for years, and the immune system, losing stamina, eventually collapses.

``That the surface is, for many years, relatively calm is a tribute to the heroic efforts of the immune system,'' researcher Simon Wain-Hobson from the Pasteur Institute wrote in an editorial published with the Nature studies.

Viral load testing has also told researchers much about the progress of disease. A pile of new studies presented in Vancouver and elsewhere indicate that a high viral load at the beginning of HIV infection is a solemn harbinger that AIDS will come sooner rather than later.