Cerebrum Summer 2020

Millions, perhaps even billions, of individuals are infected with different viruses all the time, and there’s never any issue with the brain.

mention inflammatory syndromes observed in the brain. “The blood-brain barrier is made up of blood vessels,” says Griffin. “So, if a virus can replicate in the cells of blood vessels,

compromised by viral infection. The lungs may not be able to supply sufficiently oxygenated blood to the brain, resulting in ischemia and cell death. The failure of those vital systems may also lead to more blood clots. Sherry Chou, M.D., an associate professor of Critical Care Medicine, Neurology, and Neurosurgery at the University of Pittsburgh Medical Center, says anecdotal evidence suggests that Covid-19 patients may be more prone to stroke. “Right now, this is a hunch, based on what physicians are seeing, that needs to be investigated further,” she says. “But, that said, we don’t fully understand what might be behind this phenomenon if it does exist. Could the blood vessels be infected, leading to clots? Could it be the fact that these patients are sick enough that organs start failing which means the clotting system isn’t doing what it is supposed to do and that’s the issue? We just don’t know yet.”

it has a rather direct entrance to the brain. But it could also come into the brain from cells in the blood that are allowed to cross the blood-brain barrier. It could come in through the olfactory neurons in the nose, which project to the rest of the brain. Given the number of direct approaches available, it’s actually amazing that we don’t see viruses causing neurological issues more often.” But it’s just as possible that Covid-19

Sherry Chou / University of Pittsburgh

is not infecting the brain directly, causing neurological impairment

through secondary pathways. One hypothesis that many hold is that damage comes from an overactive immune response to the novel coronavirus, a so-called “cytokine storm.” Proinflammatory cytokines, proteins produced by immune cells to fight off the virus, are released in overwhelming numbers and intensity at an infection site, enter the bloodstream, and produce severe and destructive inflammation in cells and tissues. “Sometimes damage comes from the inflammatory process and immune response—that’s really the culprit,” says Griffin. “The immune system is there to get rid of the virus. But sometimes the kinds of molecules it produces to fight off the virus can be just as detrimental to the cells as the virus is. It’s a bit of a double-edged sword.” Finally, some of the brain-related effects documented with Covid-19 may be the result of other bodily systems being

Damage Now, Damage Later Viruses may also set the brain up for later problems. When Richard Smeyne, Ph.D., a neuroscientist at Thomas Jefferson University who specializes in Parkinson’s disease, viewed a video of a duck infected with bird flu (H5N1), his first thought was, “This bird has Parkinson’s disease.” After studying the brains of infected animals, he discovered the virus had the ability to directly infiltrate and destroy cells in the

Richard Smeyne / Thomas Jefferson University

substantia nigra, the same part of the brain affected by the neurodegenerative disorder. While human beings with H5N1 did not show full-blown Parkinson’s disease, they did often

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