Making a compelling case for the expected long-term effects on the brain and nervous system by the COVID virus, new research that included scientists of Indian origin and reviewed a century of data showed that COVID-19 is likely to impact the brain in the long run.

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The question is to what degree and under what form. Even mild COVID-19 infection may have negative effects on the brain in the long term, according to researchers from the University of Texas Health Science Center at San Antonio (UT Health San Antonio) in the US. "Since the flu pandemic of 1917 and 1918, many of the flu-like diseases have been associated with brain disorders," said study lead author Gabriel A de Erausquin. "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," said de Erausquin, a professor of neurology.

He said that it is becoming clear that the damage done by the pandemic will not be limited to acute effects, such as delirium in the hospital, but will have chronic consequences that impact many individuals' quality of life and independence. The coronavirus is known to enter cells via receptors called ACE2. The highest concentration of ACE2 receptors is in the olfactory bulb, the brain structure involved in the sense of smell. "The basic idea of our study is that some of the respiratory viruses have an affinity for nervous system cells," said senior author Sudha Seshadri, professor of neurology in the Long School of Medicine at UT Health San Antonio. "Olfactory cells are very susceptible to viral invasion and are particularly targeted by SARS-CoV-2, and that's why one of the prominent symptoms of COVID-19 is loss of smell," Seshadri added.

The olfactory bulb connects with the hippocampus, a brain structure primarily responsible for short-term memory, said the article published in 'Alzheimer's & Dementia: The Journal of the Alzheimer's Association'. "The trail of the virus, when it invades the brain, leads almost straight to the hippocampus," de Erausquin said. 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," de Erausquin said.

The Alzheimer's Association is funding the initial work of a consortium of experts from more than 30 countries to understand how COVID-19 increases the risk, severity, pace, and progression of neurodegenerative diseases such as Alzheimer's and psychiatric diseases including depression. Consortium members will enroll study participants selected from a pool of millions of confirmed COVID-19 cases documented in hospitals worldwide. Participants will be evaluated on a host of measures at their initial appointment and again at six, nine and 18 months. "The under-recognised medical history of these viruses over the last century suggests a strong link to brain diseases that affect memory and behavior," said Maria C. Carrillo, Alzheimer's Association chief science officer and a co-author of the paper. "In this difficult time, we can create a 'silver lining' by capitalising 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," Carrillo added.