Jan. 5 (UPI) -- An international group of researchers called Tuesday for studies to explore the potential long-term effects of COVID-19 on the brain.
Such studies are needed based on earlier research, which has documented brain inflammation, or encephalitis, in patients with severe illness from the new coronavirus, they said in a commentary published by the journal Alzheimer's & Dementia.
Some patients hospitalized with serious cases of infection also suffered strokes, according to research.
It's believed this brain damage is not caused by the virus, but by the body's immune response to it -- and it can cause death in some patients, studies have found.
"Since the flu pandemic of 1917 and 1918, many of the flu-like diseases have been associated with brain disorders," including H1N1 and the first SARS, commentary co-author Dr. Gabriel A. de Erausquin said in a statement.
"COVID-19 is also known to impact the brain and nervous system," said de Erausquin, professor of neurology at the University of Texas Health Science Center at San Antonio.
The group, which includes researchers from Nottingham and Leicester universities in England, is part of a team of researchers from more than 30 countries exploring how COVID-19 increases the risk, severity, pace and progression of neuro-degenerative diseases such as Alzheimer's and psychiatric diseases, including depression.
The study will collect information over the next two to three years, and initial results are expected in early 2022, according to the researchers.
Participants in the Alzheimer's Association-funded study will be evaluated based on cognition, behavior and, when possible, brain volumes as measured by magnetic resonance imaging.
COVID-19 is known to enter cells via receptors called ACE2, which are located in the olfactory bulb, the brain structure involved in the sense of smell.
The olfactory bulb connects with the hippocampus, a brain structure primarily responsible for short-term memory, and this connection may be the source of cognitive impairment symptoms with severe COVID-19, the researchers said.
Loss of sense of smell is one of the key symptoms of COVID-19.
"The basic idea of our study is that some of the respiratory viruses have affinity for nervous system cells," co-author Dr. Sudha Seshadri said in a statement.
"Olfactory cells are very susceptible to viral invasion and are particularly targeted by [COVID-19]," said Seshadri, a professor of neurology at UT Health San Antonio.
Postmortem examination of patients who have died from COVID-19 have revealed evidence of the virus in the brain, according to the researchers.
MRI scans of these patients also have revealed lesions, or damage, in different regions of the brain, they said.
Based on these findings, it is becoming clear that the damage done by COVID-19 is not limited to immediate effects such as delirium in the hospital but may have chronic, long-term consequences that could impact patients' quality of life, de Erausquin said.
"The under-recognized medical history of [flu-like] viruses over the last century suggests a strong link to brain diseases that affect memory and behavior," Alzheimer's Association chief science officer Maria C. Carrillo said in a statement.
"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," she said.