Newsday - February 6, 2001
Laurie Garrett
Chicago-The brain and central nervous system appear to be a special target of the AIDS virus, and constitute a major hiding place in which the virus lurks when patients take seemingly successful rounds of medicine.
Several researchers presented striking, and deeply puzzling findings about HIV, the virus that causes AIDS, and its effects on the neurons of the brain and spinal cord at this week's eighth annual Retrovirus Conference in Chicago.
The emerging consensus is that "the central nervous system is a reservoir for HIV, probably in the macrophages [cells] in the brain...but there are also other viruses in there that we cannot detect until autopsy," Dr. Dana Gabuzda of the Dana- Farber Cancer Institute in Boston explained in an interview.
Some of the drugs widely used to treat HIV can make their way into the brain, but such profound neurological disorders as seizures, dementia, death of brain cells on a massive scale and absence of feeling in legs and arms leading to loss of such basic functions as walking are common in HIV patients. Explaining how and why these terrible events occur, despite otherwise successful anti-HIV therapy, has become an increasingly urgent preoccupation of AIDS clinical researchers.
Even monkeys infected with the simian form of the AIDS virus experience profound headaches and neurological disorders, Dr. Christopher Pilcher of the University of North Carolina said in a speech yesterday. And about half of all humans infected with HIV battle severe headaches resulting from viral infection of their brains.
A large-scale Italian survey last year of 311 people with HIV found that about half of them, whether or not they were taking antiviral medicines, experienced some form of encephalitis (inflammation), though most were unaware of the brain disease: Their brain lesions, reflex changes and behavior effects were only noted under careful clinical examination, said Dr. Anna Ammassari of the National Institute of Infectious Diseases in Rome. Curiously, she noted, patients who were taking anti-HIV drugs were more likely over time to experience some form of brain inflammation, though the most severe types were seen in those who were either failing their drug treatments or weren't taking any drugs to treat HIV, at all.
In some cases, what appears to be an HIV-created neuropathy is actually a side effect of the drugs patients take to control the virus. Physicians often have difficulty discriminating between the two, researchers from St. Vincent's Hospital in Sydney, Australia, explained. And that might lead to overestimates of just how much brain and nerve damage is actually caused directly by the virus.
Spanish surveys of HIV patients who have suffered encephalitis show that those on anti-HIV drugs live an average of 4.5 years after detection of their brain disease, vs. a matter of months in untreated HIV patients. That means, Gabuzda said, the drugs do eventually get into the brain.
But brain cells keep dying. Scientists here offered several explanations, each more complicated than the last. The virus does not directly eat up neurons. Rather, the brain cells die because various chemicals released by virally infected cells trigger suicide mechanisms in the neurons. So the brain cells, ultimately, kill themselves.
"There is evidence that there are HIV strains that have greater capacity to produce neurological damage," Gabuzda added. And the chemicals released in the infected brain, "cause an inflammation reaction not unlike things we see with other forms of encephalitis, dementia and Alzheimer's disease."
The hope is that by gaining a better understanding of the inflammation produced with HIV infection scientists may find clues to the causes of other severe brain diseases, including Alzheimer's.
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