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Study Detects Brain Virus in HIV-Positive Patients

For release: Tuesday, May 5, 1992

Scientists at the National Institute of Neurological Disorders and Stroke (NINDS) have identified a potentially fatal virus in the bloodstream in half of a small group of HIV-positive patients without neurological symptoms, they announced today at the annual meeting of the American Academy of Neurology in San Diego.

The virus causes a fatal brain disease called progressive multifocal leukoencephalopathy or PML. PML, which triggers dementia and movement problems, currently affects about 3 to 5 percent of all patients with AIDS, killing about 1,000 AIDS patients each year. There is currently no effective treatment.

"Our findings tell us that many more people are at risk for PML than we previously believed," says NINDS scientist Eugene O. Major, Ph.D. "They also provide us with a missing link as to where the latent virus hides and how it enters the brain."

Although the PML virus infects about 85 percent of all Americans by the age of 9, most people do not develop PML unless they have severe immune problems, such as those caused by AIDS, leukemia, or organ transplantation. Instead, the virus usually stays dormant and harmless, hidden in a site outside the brain and nervous system. Although antibodies to the PML virus are common, the dormant virus cannot be detected in the bloodstream in most people.

In the study, scientists detected pieces of the PML virus in white blood cells from 23 of 46 patients who were HIV-positive but who did not have PML symptoms. White blood cells are part of the body's immune system and normally play an important role in stopping disease. Scientists also checked for the virus in PML patients and control group of Parkinson's disease patients. No signs of the PML virus were found in white blood cells from 30 Parkinson's disease patients; fragments of PML virus were uncovered in 17 of the 19 PML patients.

"The findings are unexpected. We may have to eventually test all HIV-positive patients for the PML virus to identify those who could be at risk before they develop symptoms," says Carlo Tornatore, M.D., the NINDS neurologist who led the study. Also, Dr. Tornatore adds "the direct and non-invasive test we developed for the study will help doctors diagnose PML." Previously, he explains, PML diagnosis required a brain biopsy, a highly invasive and risky test not feasible in many patients.

Because the results reveal the virus' hideout, they could also offer new routes for research to prevent PML, scientists say. "We have identified the immune system as the reservoir where the latent virus hides outside the nervous system. It may be too late to stop PML once the virus gets in the brain. Our results suggest that, once we identify the specific immune cells, we might be able stop these infected cells before they get in," says Dr. Major.

NINDS scientists, in collaboration with scientists at the University of Miami, are continuing to follow the HIV-positive patients to learn if they develop PML.

The NINDS, one of the 13 National Institutes of Health in Bethesda, Maryland, is the primary supporter of brain and nervous system research in the United States.

Last Modified August 7, 2009