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Scientists consider the SARS-CoV-2 virus a “neurotropic” virus, because it can enter nerve cells. Neurotropic viruses include the mumps, rabies, and Epstein-Barr viruses. While some neurotropic viruses cause milder symptoms, others can cause swelling in the brain, paralysis, and death.
Some flu-like viruses are neurotropic and similar in structure to the novel coronavirus. As such, researchers looked at these viruses to try to gain insight into what type of long-term effects to expect in people who have recovered from COVID-19.
“Since the flu pandemic of 1917 and 1918, many of the flu-like diseases have been associated with brain disorders,” says lead author Dr. Gabriel A. de Erausquin.
Dr. de Erausquin, who is a neurology professor at the University of Texas Health Science Center at San Antonio, explains: “Those respiratory viruses included H1N1 and SARS-CoV. The SARS-CoV-2 virus, which causes COVID-19, is also known to impact the brain and nervous system.”
While losing the sense of smell may not seem serious at first, it is still important, since it is tied directly to brain function.
To enter cells, SARS-CoV-2 binds to ACE2 receptors on cell membranes. The olfactory bulb, which is the part of the brain receiving sensations of smell, harbors a high concentration of these receptors. The olfactory bulb also has strong connections to the hippocampus — the area responsible for memory.
According to Dr. de Erausquin, “The trail of the virus, when it invades the brain, leads almost straight to the hippocampus.”
“That is believed to be one of the sources of the cognitive impairment observed in COVID-19 patients. We suspect it may also be part of the reason why there will be an accelerated cognitive decline over time in susceptible individuals,” he adds.
Among severe neurological issues during SARS-CoV-2 infection, patients may develop fluid on the brain, inflammation in the brain, and seizures.
COVID-19 can cause severe damage to the lungs, and that damage can be irreversible. However, according to the authors’ research, it appears that the possible fallout from COVID-19 may extend far beyond lung damage.
The authors write that “respiratory problems due to SARS-CoV-2 are thought to be due in part to brain stem dysregulation, as are possibly some of the gastrointestinal symptoms.”
Based on the idea that COVID-19 can cause damage to the brain, it is possible that people who have had the novel coronavirus but were either asymptomatic or experienced mild symptoms may face problems down the road.
However, because COVID-19 is a new disease, scientists will need to carry out longer-term studies to confirm these theories.
“As the Alzheimer’s & Dementia article points out, the under-recognized medical history of these viruses over the last century suggests a strong link to brain diseases that affect memory and behavior,” comments Dr. Maria C. Carrillo, Alzheimer’s Association chief science officer and paper co-author.
“In this difficult time, we can create a ‘silver lining’ by capitalizing on the Alzheimer’s Association’s global reach and reputation to bring the research community together to illuminate COVID-19’s long-term impact on the brain,” says Dr. Carrillo.
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