Virus World

Research shows that even mild COVID-19 can lead to the equivalent of seven years of brain aging. From the very early days of the pandemic, brain fog emerged as a significant health condition that many experience after COVID-19. Brain fog is a colloquial term that describes a state of mental sluggishness or lack of clarity and haziness that makes it difficult to concentrate, remember things and think clearly. Fast-forward four years and there is now abundant evidence that being infected with SARS-CoV-2 – the virus that causes COVID-19 – can affect brain health in many ways. In addition to brain fog, COVID-19 can lead to an array of problems, including headaches, seizure disorders, strokes, sleep problems, and tingling and paralysis of the nerves, as well as several mental health disorders. A large and growing body of evidence amassed throughout the pandemic details the many ways that COVID-19 leaves an indelible mark on the brain. But the specific pathways by which the virus does so are still being elucidated, and curative treatments are nonexistent. Now, two new studies published in the New England Journal of Medicine shed further light on the profound toll of COVID-19 on cognitive health.....

Cognitive impairment is one of the most prevalent symptoms of post Severe Acute Respiratory Syndrome COronaVirus 2 (SARS-CoV-2) state, which is known as Long COVID. Advanced neuroimaging techniques may contribute to a better understanding of the pathophysiological brain changes and the underlying mechanisms in post-COVID-19 subjects. We aimed at investigating regional cerebral perfusion alterations in post-COVID-19 subjects who reported a subjective cognitive impairment after a mild SARS-CoV-2 infection, using a non-invasive Arterial Spin Labeling (ASL) MRI technique and analysis. Using MRI-ASL image processing, we investigated the brain perfusion alterations in 24 patients (53.0 ± 14.5 years, 15F/9M) with persistent cognitive complaints in the post COVID-19 period.

Voxelwise and region-of-interest analyses were performed to identify statistically significant differences in cerebral blood flow (CBF) maps between post-COVID-19 patients, and age and sex matched healthy controls (54.8 ± 9.1 years, 13F/9M). The results showed a significant hypoperfusion in a widespread cerebral network in the post-COVID-19 group, predominantly affecting the frontal cortex, as well as the parietal and temporal cortex, as identified by a non-parametric permutation testing (p < 0.05, FWE-corrected with TFCE). The hypoperfusion areas identified in the right hemisphere regions were more extensive. These findings support the hypothesis of a large network dysfunction in post-COVID subjects with cognitive complaints. The non-invasive nature of the ASL-MRI method may play an important role in the monitoring and prognosis of post-COVID-19 subjects.

Published in Scientific Reports (April 10, 2023):

https://doi.org/10.1038/s41598-023-32275-3 

Neurological manifestations are common in COVID-19, the disease caused by SARS-CoV-2. Despite reports of SARS-CoV-2 detection in the brain and cerebrospinal fluid of COVID-19 patients, it is still unclear whether the virus can infect the central nervous system, and which neuropathological alterations can be ascribed to viral tropism, rather than immune-mediated mechanisms. Here, we assess neuropathological alterations in 24 COVID-19 patients and 18 matched controls who died due to pneumonia/respiratory failure. Aside from a wide spectrum of neuropathological alterations, SARS-CoV-2-immunoreactive neurons were detected in the dorsal medulla and in the substantia nigra of five COVID-19 subjects. Viral RNA was also detected by real-time RT-PCR. Quantification of reactive microglia revealed an anatomically segregated pattern of inflammation within affected brainstem regions, and was higher when compared to controls. While the results of this study support the neuroinvasive potential of SARS-CoV-2 and characterize the role of brainstem inflammation in COVID-19, its potential implications for neurodegeneration, especially in Parkinson’s disease, require further investigations.

Published (Feb. 13, 2023) in npj Parkinson's Disease:

https://doi.org/10.1038/s41531-023-00467-3 

New research from the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King's College London has found evidence of small hemorrhages in the brain tissue of fetuses during the peak of COVID-19 cases in the UK. The research, published in Brain, found that the hemorrhages are linked to a reduction in blood vessel integrity. The cause of these hemorrhages is unclear, however possible explanations might be as a direct consequence of the infection or an indirect consequence of the maternal immune response. The study suggests that COVID-19 might affect the fetal brain during the earliest stages of gestation, highlighting a need for further study into the potential impact on subsequent neurological development. The researchers studied 26 samples of human fetal tissue with observed hemorrhages from a total of 661 samples collected between July 2020 and April 2022. It was established that the COVID-19 virus was present in all of the hemorrhagic samples. The majority of the hemorrhagic samples came from donated fetal tissue between the late first and early second trimester of gestation—a particularly important period of human fetal brain development during which the tight junctions between endothelial cells of the blood vessels increase to form the blood brain barrier, the semipermeable barrier that protects the brain from foreign substances.

Upon further study, the integrity of the blood vessels within the hemorrhagic samples was found to be considerably lower than the non-infected samples, ultimately providing an explanation as to why bleeds could be seen in the samples. "While hemorrhages do occasionally occur in developing brains, it is extremely unusual for there to be this many instances within a 21 month period. It is now of the utmost importance that we follow up with children that were prenatally exposed to COVID-19 so that we can establish if there are any long-lasting neurodevelopmental effects," said Dr. Katie Long, the study's lead investigator from King's IoPPN. Marco Massimo, the study's first author from King's IoPPN said, "Our findings suggest that there is an association between the early development of human fetal brain tissue and vulnerability to infection from COVID-19." Professor Lucilla Poston CBE, Professor of Maternal & Fetal Health at King's College London, said, "We know that severe viral infection may influence the fetal brain, but this important study is the first to suggest that this may occur in pregnancies affected by COVID infection. Whatever the cause, a direct effect of the virus or an indirect consequence of maternal infection, this study highlights the need for pregnant women to be vaccinated against COVID-19, thus avoiding complications for both mother and baby." Dr. Long concludes, "While we haven't yet been able to establish clear causation, we certainly feel that it highlights a need for expectant mothers to take extra precautions at a time when cases are on the rise."

Cited study published in Brain (Jan. 16, 2023):

https://doi.org/10.1093/brain/awac372 

A University of Queensland-led study finds COVID-19 activates a similar inflammatory response to Parkinson's disease, but scientists warn it's too early to cause alarm with more work needed into how the virus affects the brain.  Lead researcher Trent Woodruff, from the university's neuro-inflammation laboratory, said the findings illustrated a potential future risk for neurodegenerative conditions in people who had been infected with SARS-CoV-2, the virus that causes COVID-19.  But he said it was too early for the study to cause alarm, with much more work needed into how the virus may affect the human brain. "It may explain some of the symptoms that are occurring in patients with long COVID and brain fog," Professor Woodruff said. "It's certainly something that we should be looking at and monitoring.  UQ researchers studied the effect of SARS-CoV-2 on the brain's immune cells, known as microglia, which are key cells involved in the progression of brain diseases, such as Parkinson's and Alzheimer's disease. They grew microglia from the donor blood of healthy volunteers and infected the cells with the virus.  "We identified that the cells became highly inflammatory, we like to think of them as angry microglia, and they turned on a pathway called the inflammasome, which we have previously shown is linked to certain brain diseases, like Parkinson's and Alzheimer's," Professor Woodruff said. "It didn't matter whose blood it was or whose cells we looked at, all the cells reacted quite strongly to this virus."  The researchers also compared mice infected with SARS-CoV-2 and those which had not been infected with the virus. They found inflammasome activation in the brains of the mice infected with SARS-CoV-2.

Possible treatment also identified

But the researchers, including Professor Woodruff's UQ colleague Eduardo Albornoz Balmaceda, also identified a potential treatment. They gave the infected mice a UQ-developed drug, which is in human trials of Parkinson's disease patients.  The drug blocked the inflammatory pathway in the mouse brain that had been activated by COVID-19. Dr Albornoz Balmaceda likened the effect of the drug to dousing "a fire" in the brain. "The drug reduced inflammation in both virus-infected COVID-19 mice and the microglia cells from humans, suggesting a possible treatment approach to prevent neuro-degeneration in the future," he said.  Professor Woodruff said "dozens" of other drugs, designed to block the inflammasome pathway, were in development worldwide. "We're hopeful that one of these therapies may make it all the way through to clinical application," he said. The researchers said it was impossible to know from their study, published in the journal Molecular Psychiatry, whether inflammation in the brains of people infected with SARS-CoV-2 dissipated once the virus was cleared from the body. "It may be that in most individuals that this is entirely what's happening," he said.  "There's a lot more research to be done," Professor Woodruff said. "Our research is really just the first piece of the puzzle. I think it's important to start looking clinically in some of these individuals that may be susceptible to see if what we're discovering in the lab may also be true out in the population." Infectious disease specialist Paul Griffin, who was not involved in the study, described the research as “extremely valuable” but was cautious about its findings. “This is a good platform upon which more research can be based but it’s still very early,” Dr Griffin said. “A lot of this makes sense with what we understand how the virus causes problems. “A lot of the manifestations from the heart issues to the lung issues to the brain issues, they’re probably all inflammatory in nature.” Dr Griffin said the study was another reason why it was important “that we still do what we can to reduce the burden” of the pandemic virus.

Cited research published in molecular Psychiatry (Nov. 1, 2022):

https://doi.org/10.1038/s41380-022-01831-0 

New research helps explain why long COVID can occur in people who had mild or asymptomatic COVID-19 cases.  The coronavirus that causes COVID-19, SARS-CoV-2, can spread within days from the airways to the heart, brain and almost every organ system in the body, where it may persist for months, a study found. In what they describe as the most comprehensive analysis to date of the virus’s distribution and persistence in the body and brain, scientists at the U.S. National Institutes of Health said they found the pathogen is capable of replicating in human cells well beyond the respiratory tract. The results, released online Saturday in a manuscript under review for publication in the journal Nature, point to delayed viral clearance as a potential contributor to the persistent symptoms wracking so-called long COVID sufferers. Understanding the mechanisms by which the virus persists, along with the body’s response to any viral reservoir, promises to help improve care for those afflicted, the authors said. “This is remarkably important work,” said Ziyad Al-Aly, director of the clinical epidemiology center at the Veterans Affairs St. Louis Health Care System in Missouri, who has led separate studies into the long-term effects of COVID-19. “For a long time now, we have been scratching our heads and asking why long COVID seems to affect so many organ systems. This paper sheds some light, and may help explain why long COVID can occur even in people who had mild or asymptomatic acute disease.” The findings haven’t yet been reviewed by independent scientists, and are mostly based on data gathered from fatal COVID cases, not patients with long COVID or “post-acute sequelae of SARS-CoV-2,” as it’s also called.

Contentious Findings

The coronavirus’s propensity to infect cells outside the airways and lungs is contested, with numerous studies providing evidence for and against the possibility.  The research undertaken at the NIH in Bethesda, Maryland, is based on extensive sampling and analysis of tissues taken during autopsies on 44 patients who died after contracting the coronavirus during the first year of the pandemic in the U.S.  The burden of infection outside the respiratory tract and time to viral clearance isn’t well characterized, particularly in the brain, wrote Daniel Chertow, who runs the NIH’s emerging pathogens section, and his colleagues. The group detected persistent SARS-CoV-2 RNA in multiple parts of the body, including regions throughout the brain, for as long as 230 days following symptom onset. This may represent infection with defective virus, which has been described in persistent infection with the measles virus, they said.  In contrast to other COVID autopsy research, the NIH team’s post-mortem tissue collection was more comprehensive and typically occurred within about a day of the patient’s death. 

Culturing Coronavirus

The NIH researchers also used a variety of tissue preservation techniques to detect and quantify viral levels, as well as grow the virus collected from multiple tissues, including lung, heart, small intestine and adrenal gland from deceased COVID patients during their first week of illness. “Our results collectively show that while the highest burden of SARS-CoV-2 is in the airways and lung, the virus can disseminate early during infection and infect cells throughout the entire body, including widely throughout the brain,” the authors said. The researchers posit that infection of the pulmonary system may result in an early “viremic” phase, in which the virus is present in the bloodstream and is seeded throughout the body, including across the blood-brain barrier, even in patients experiencing mild or no symptoms. One patient in the autopsy study was a juvenile who likely died from unrelated seizure complications, suggesting infected children without severe COVID-19 can also experience systemic infection, they said.

Immune Response

The less-efficient viral clearance in tissues outside the pulmonary system may be related to a weak immune response outside the respiratory tract, the authors said.  SARS-CoV-2 RNA was detected in the brains of all six autopsy patients who died more than a month after developing symptoms, and across most locations evaluated in the brain in five, including one patient who died 230 days after symptom onset. The focus on multiple brain areas is especially helpful, said Al-Aly at the Veterans Affairs St. Louis Health Care System.  “It can help us understand the neurocognitive decline or ‘brain fog’ and other neuropsychiatric manifestations of long COVID,” he said. “We need to start thinking of SARS-CoV-2 as a systemic virus that may clear in some people, but in others may persist for weeks or months and produce long COVID -- a multifaceted systemic disorder.”

Preprint (Dec. 20, 2021) of the research cited available at:

https://assets.researchsquare.com/files/rs-1139035/v1_covered.pdf?c=1640020576 

It’s not just the lungs — the pathogen may enter brain cells, causing symptoms like delirium and confusion, scientists reported. The coronavirus targets the lungs foremost, but also the kidneys, liver and blood vessels. Still, about half of patients report neurological symptoms, including headaches, confusion and delirium, suggesting the virus may also attack the brain. A new study offers the first clear evidence that, in some people, the coronavirus invades brain cells, hijacking them to make copies of itself. The virus also seems to suck up all of the oxygen nearby, starving neighboring cells to death. It’s unclear how the virus gets to the brain or how often it sets off this trail of destruction. Infection of the brain is likely to be rare, but some people may be susceptible because of their genetic backgrounds, a high viral load or other reasons. “If the brain does become infected, it could have a lethal consequence,” said Akiko Iwasaki, an immunologist at Yale University who led the work. The study was posted online on Wednesday and has not yet been vetted by experts for publication. But several researchers said it was careful and elegant, showing in multiple ways that the virus can infect brain cells.

Scientists have had to rely on brain imaging and patient symptoms to infer effects on the brain, but “we hadn’t really seen much evidence that the virus can infect the brain, even though we knew it was a potential possibility,” said Dr. Michael Zandi, consultant neurologist at the National Hospital for Neurology and Neurosurgery in Britain. “This data just provides a little bit more evidence that it certainly can.” Dr. Zandi and his colleagues published research in July showing that some patients with Covid-19, the illness caused by the coronavirus, develop serious neurological complications, including nerve damage. In the new study, Dr. Iwasaki and her colleagues documented brain infection in three ways: in brain tissue from a person who died of Covid-19, in a mouse model and in organoids — clusters of brain cells in a lab dish meant to mimic the brain’s three-dimensional structure. 

Other pathogens — including the Zika virus — are known to infect brain cells. Immune cells then flood the damaged sites, trying to cleanse the brain by destroying infected cells. The coronavirus is much stealthier: It exploits the brain cells’ machinery to multiply, but doesn’t destroy them. Instead, it chokes off oxygen to adjacent cells, causing them to wither and die. The researchers didn’t find any evidence of an immune response to remedy this problem. “It’s kind of a silent infection,” Dr. Iwasaki said. “This virus has a lot of evasion mechanisms.” These findings are consistent with other observations in organoids infected with the coronavirus, said Alysson Muotri, a neuroscientist at the University of California, San Diego, who has also studied the Zika virus. The coronavirus seems to rapidly decrease the number of synapses, the connections between neurons. “Days after infection, and we already see a dramatic reduction in the amount of synapses,” Dr. Muotri said. “We don’t know yet if that is reversible or not.” The virus infects a cell via a protein on its surface called ACE2. That protein appears throughout the body and especially in the lungs, explaining why they are favored targets of the virus. Previous studies have suggested, based on a proxy for protein levels, that the brain has very little ACE2 and is likely to be spared. But Dr. Iwasaki and her colleagues looked more closely and found that the virus could indeed enter brain cells using this doorway.  “It’s pretty clear that it is expressed in the neurons and it’s required for entry,” Dr. Iwasaki said.  Her team then looked at two sets of mice — one with the ACE2 receptor expressed only in the brain, and the other with the receptor only in the lungs. When researchers introduced the virus into these mice, the brain-infected mice rapidly lost weight and died within six days. The lung-infected mice did neither...

UK neurologists publish details of mildly affected or recovering patients with serious or potentially fatal brain conditions. Doctors may be missing signs of serious and potentially fatal brain disorders triggered by coronavirus, as they emerge in mildly affected or recovering patients, scientists have warned. The cases, published in the journal Brain, revealed a rise in a life-threatening condition called Acute Disseminated Encephalomyelitis (Adem), as the first wave of infections swept through Britain. At UCL’s Institute of Neurology, Adem cases rose from one a month before the pandemic to two or three per week in April and May. One woman, who was 59, died of the complication.

A dozen patients had inflammation of the central nervous system, 10 had brain disease with delirium or psychosis, eight had strokes and a further eight had peripheral nerve problems, mostly diagnosed as Guillain-Barré syndrome, an immune reaction that attacks the nerves and causes paralysis. It is fatal in 5% of cases. “We’re seeing things in the way Covid-19 affects the brain that we haven’t seen before with other viruses,” said Michael Zandi, a senior author on the study and a consultant at the institute and University College London Hospitals NHS foundation trust. “What we’ve seen with some of these Adem patients, and in other patients, is you can have severe neurology, you can be quite sick, but actually have trivial lung disease,” he added. “Biologically, Adem has some similarities with multiple sclerosis, but it is more severe and usually happens as a one-off. Some patients are left with long-term disability, others can make a good recovery.” The cases add to concerns over the long-term health effects of Covid-19, which have left some patients breathless and fatigued long after they have cleared the virus, and others with numbness, weakness and memory problems...

Original Study Published in Brain (July 8, 2020):

https://doi.org/10.1093/brain/awaa240

Studies in living brain tissue found that specialized immune cells in the brain can harbor latent but replication-competent HIV.  As a part of its life cycle, human immunodeficiency virus-1 (HIV-1) inserts a copy of its DNA into human immune cells. Some of these newly infected immune cells can then transition into a dormant, latent state for a long period of time, which is known as HIV latency. Although current antiretroviral therapy (ART) against HIV can successfully block the virus from replicating further, it cannot eradicate latent HIV. If treatment is discontinued, the virus can rebound from latency and reignite the progression of HIV infection to AIDS. Scientists at the HIV Cure Center at the UNC School of Medicine, University of California, San Diego (UCSD), Emory University, and the University of Pennsylvania, have been searching for where exactly these latent cells are hiding in the body. Their newly reported studies indicate that brain microglial (BM)—specialized brain-resident immune cells with a decade-long lifespan—can serve as a stable viral reservoir for latent HIV. “We now know that microglial cells serve as a persistent brain reservoir,” said Yuyang Tang, PhD, assistant professor of medicine in the division of infectious diseases and member of the UNC HIV Cure Center. “This had been suspected in the past, but proof in humans was lacking. Our method for isolating viable brain cells provides a new framework for future studies on reservoirs of the central nervous system, and, ultimately, efforts towards the eradication of HIV.” Tang is first author of the team’s published paper in The Journal of Clinical Investigation, which is titled, “Brain microglia serve as persistent HIV reservoir despite durable antiretroviral therapy.”

HIV is a tricky virus to study. During infection, the virus specifically targets CD4+ lymphocytes which are the key coordinators of the immune response. Over time, the virus kills enough CD4+ cells to cause immunodeficiency. Past research has shown that latent HIV can hide within a few of the surviving CD4+ T cells throughout the body and the bloodstream. However, it’s been suspected that there are other viral reservoirs hidden within the central nervous system (CNS) in people with HIV who are receiving effective ART. But as the authors noted, “… rigorous evidence of viral persistence in the CNS cells of humans on durable suppressive ART is incomplete … Brain microglia (MG) may serve as a human immunodeficiency virus 1 (HIV) reservoir and ignite rebound viremia following cessation of antiretroviral therapy (ART), but they have yet to be proven to harbor replication-competent HIV. Unlike peripheral blood cells, it is extremely difficult to access and analyze brain tissues for the study of HIV reservoirs. Since these types of cells cannot be safely sampled in people taking ART, the potential viral reservoir in the brain has remained an enigma for many years. For their reported research the team first studied the brains of macaques infected with simian immunodeficiency virus (SIV), a virus that is closely related to HIV, from the Yerkes National Primate Research Center at Emory University to get a better understanding of how to extract and purify viable cells from primate brain tissue. The researchers used physical separation techniques and antibodies to selectively remove cells that were expressing microglial surface markers. Then, they isolated and separated the highly pure brain myeloid cells (BrMCs) from the CD4+ cells that were passing through the brain tissue. Using these techniques, researchers then obtained samples that were donated by HIV+ people (people with HIV; PWH) who were enrolled in “The Last Gift” Study at UCSD. As a part of this unique and important effort, altruistic HIV+ people, who are taking ART but suffering from other terminal illnesses, will their bodies to further the HIV research project.

“ … we first developed protocols to isolate highly pure populations of BrMCs and MG from the tissues of nonhuman primates (NHPs),” the authors explained. “We then adapted these protocols to the study of human brain tissues containing large numbers of viable cells after rapid autopsy to explore whether human BrMCs produce replication-competent HIV.” Co-author David Margolis, MD, the Sarah Kenan distinguished professor of medicine, microbiology & immunology, and epidemiology, further noted, “The samples are from people living with HIV, who are on therapy but facing a fatal disease of some kind. They were willing to not just donate their bodies to science, but also participate in the research program in the months leading up to their death. It’s an extraordinary program that made this critical research possible.” The scientists’ findings confirmed that MGs from an individual with HIV, being treated using ART, harbored replication-competent HIV. They acknowledged that although their study was limited by the small number of available samples from human donors on ART, they believe that the findings are consistent with NHP studies. “Our observations support the concept that brain MG are a stable reservoir of quiescent infection and may be a source of viral rebound upon treatment interruption,” they concluded. “Future efforts to clear HIV infection will have to include assessments of the persistence of HIV within CNS MG.” Now that the researchers know that latent HIV can take refuge in microglial cells in the brain, they are now considering plans to target this type of reservoir. Since latent HIV in the brain is radically different from the virus in the periphery, researchers believe that it has adapted special characteristics to replicate in the brain.

Reporting in their paper, the team noted, “Phenotyping studies characterized brain-derived virus as macrophage tropic based on the ability of the virus to infect cells expressing low levels of CD4. The lack of genetic diversity in virus from the brain suggests that this macrophage-tropic lineage quickly colonized brain regions.” NF-κB signaling is one of the critical signaling pathways that control HIV expression elsewhere in the body. When NF-κB signaling is “turned off,” HIV enters latency in the peripheral blood. However, latent HIV in the brain is not impacted by the activation of NF-κB signaling. Researchers are unsure why that is, but once an answer is found, they will be one step closer to knowing how to selectively target and eradicate the virus in the brain or peripheral blood. In addition to understanding the inner workings of the brain reservoir, the researchers are also trying to determine the true size of the latent HIV brain reservoir. “HIV is very smart,” said senior author Guochun Jiang, PhD, assistant professor in the UNC department of biochemistry and biophysics and member of the UNC HIV Cure Center. “Over time, it has evolved to have epigenetic control of its expression, silencing the virus to hide in the brain from immune clearance. We are starting to unravel the unique mechanism that allows latency of HIV in brain microglia”. Added Margolis, who is also the director of the UNC HIV Cure Center, “It is very hard to know how big the reservoir is. The problem with trying to eradicate HIV is like trying to eradicate cancer. You want to be able to get it all, so it won’t come back.”

Original research published in The Journal of Clin. Investigation (June 15, 2023):

https://doi.org/10.1172/JCI167417 

As familiar to everyone as the COVID-causing coronavirus SARS-CoV-2 has become over the past two years, feverish research is still trying to parse a lingering puzzle. How, in fact, does the pandemic virus that has so changed the world cross over into the brain after entering the respiratory system? An answer is important because neurological complaints are some of the most common in the constellation of symptoms called long COVID. The mystery centers around the fact that brain cells don’t display the receptors, or docking sites, that the virus uses to get into nasal and lung cells. SARS-CoV-2, though, may have come up with an ingenious work-around. It may completely do away with the molecular maneuverings needed to attach to and unlock a cell membrane. Instead it wields a blunt instrument in the form of nanotube “bridges”—cylinders constructed of the common protein actin that are no more than a few tens of nanometers in diameter. These tunneling nanotubes extend across cell-to-cell gaps to penetrate a neighbor and give viral particles a direct route into COVID-impervious tissue. Researchers at the Pasteur Institute in Paris demonstrated the prospects for a nanotube-mediated cell crossing in a study in a lab dish that now needs to be confirmed in infected human patients. Given further proof, the findings could explain why some people who get COVID-19 experience brain fog and other neurological symptoms. Also, if the intercellular conduits could be severed, that might prevent some of these debilitating aftereffects of infection.

The nanotube route “is a shortcut that propagates infection fast and between different organs, permissive or not permissive, to the infection,” says Chiara Zurzolo, a cell biologist at the Pasteur Institute, who conducted the study. “And it might be also a way for the virus to hide and escape the immune response.” The virus may be capable of commandeering a cell’s own nanotubes, diverting them away from other routine tasks, such as transferring lipids and proteins between cells. Early research on SARS-CoV-2 suggested that it might be able to hijack similar cell projections. A 2020 paper published in the journal Cell found that cells infected with the novel coronavirus extended out antennalike feelers called filopodia with viral particles onboard. SARS-CoV-2 typically gets into cells in the respiratory tract and elsewhere by latching its protruding “spike” protein to ACE2 receptors on their surface. Zurzolo and her team wondered if the coronavirus was using tunneling nanotubes to sneak into cells that were not studded with these receptors. To find out what was going on, the researchers took cells from monkey kidneys, infected them with SARS-CoV-2 and cultured them alongside human neurons in a lab dish. Monkey kidneys cells are commonly used to model the human respiratory tract in studies of COVID-19 because the cells display ACE2 receptors. The neurons came from a cell line that was originally cultured from a cancer called neuroblastoma. These cells lack ACE2 receptors, but after 48 hours side-by-side with coronavirus-infected kidney cells, 62.5 percent of them were infected with SARS-CoV-2. The team then used cutting-edge microscopy techniques to image how this viral transfer occurred. By tagging viral proteins with antibodies and fluorescent compounds so that they stood out, the researchers captured high-resolution images of the virus within the tunneling nanotubes that connected the cells. They could see both viral particles and little sacs called vesicles in which the virus copies itself. They also detected proteins that are part of the cellular machinery the virus uses to replicate. The imaging was so detailed that even the spike proteins that give the virus its prickly appearance were visible, the researchers reported in the journal Science Advances. Once nestled in the neuronal cells, the coronavirus was able to continue replicating.

The experiments also showed that cells infected with the coronavirus grew far more tunneling nanotubes than uninfected cells, suggesting that the virus itself spurs a cell to put out these connectors. SARS-CoV-2 isn’t the only pathogen that controls cells in this way. HIV also takes advantage of tunneling nanotubes to move between cells, and the Marburg virus triggers the growth of filopodia. “The virus is so sinister,” says Nevan Krogan, a molecular biologist at the University of California, San Francisco, who was not involved in the new research but conducted the 2020 study that found the increase in filopodia after coronavirus infection. “It’s manipulating all of our processes with a very limited genetic [repertoire].” The cellular bridges may play a role in how the virus sometimes triggers long COVID, Krogan says. Zurzolo and her team suspect that the virus enters through the nose and travels along to one of the brain’s two olfactory bulbs, which contain tissue that processes smells. The nanotubes may help the virus avoid antibodies, allowing it to linger longer in the body. “If you can manipulate enzymes that are responsible for this filopodia or nanotube formation, this could be a way to maybe have an effect on long COVID,” Krogan says. His work showed that the coronavirus increases production of the enzyme casein kinase II, which in turn helps build the protein backbone of filopodia and nanotubes. Senhwa Biosciences, a Taiwan–based drug development company, is currently conducting clinical trials of a drug called silmitasertib that inhibits casein kinase II to probe whether it has an impact on COVID-19 recovery. Meanwhile Zurzolo and her colleagues are now working to prove that their hypothesis about how SARS-CoV-2 reaches the brain occurs in actual infections. If they can do so, they may be a step closer to figuring out why, for some people, COVID-19 triggers a lingering health debacle.

Cited study published in ScienceAdvances (July 2022):

https://doi.org/10.1126/sciadv.abo0171 

We now know that covid-19 can cause neurological symptoms, ranging from brain fog and headaches to strokes. Research is beginning to reveal how this happens and hint at better treatments. From the first weeks of the covid-19 pandemic, it has been clear that the disease often causes neurological symptoms – ranging from headaches and brain fog to strokes and paralysis. Sometimes, the symptoms are short-lived; sometimes, they persist as part of long covid. We are now getting a clearer picture of covid-19’s neurological symptoms and how the SARS-CoV-2 coronavirus indirectly affects the brain, pointing the way to potential treatments...

The study, done by researchers in India, found deposits of blood, calcium and iron at abnormal levels in key regions of the brain. The study was done using MRI scans six months after an infection. People with long Covid suffer physical alterations to their brain months after clearing the initial infection, a study has shown. MRIs of patients still suffering with symptoms six months later show clusters in parts of the brain linked to fatigue, headaches and cognition. The Indian researchers behind the study say it is the first to show that Covid causes physical changes to the brain. Other studies have found that the virus can also cause changes in other organs such as the heart and lungs. Long Covid is not a specific condition with a set diagnosis, but instead an amalgamation of different symptoms with tenuous links to one-another that have been placed in the same category.   The Centers for Disease Control and Prevention (CDC) estimates that one in five adults that are infected with Covid will suffer long Covid to varying degrees.  There is no proven treatment or cure, but experts are exploring whether an alcoholism drug has benefit after showing promise in small studies.

Researchers from the the Indian Institute of Technology, in Dehli, gathered data from 46 patents who had Covid in the last six months and 30 people that had never been infected with the virus.

They found that most of the people who had recovered from Covid had changes in the circulation of tiny blood vessels in the frontal lobe and brain stem areas. These regions are involved in higher order cognitive skills such as language expression and voluntary movements. Sapna Mishra, a PhD candidate at the institute a lead researchers of the study said 'these brain regions are linked with fatigue, insomnia, anxiety, depression, headaches and cognitive problems.' The cluster obtained in the frontal lobe primarily showed changes in white matter. White matter is found in the deepest tissues of the brain and is made up of millions of nerve fibers that connects parts of the brain and links the brain to the spinal cord Through changes in white matter, the brain finds it harder to transfer information, leading to difficulties with memory, mobility and balance. These clusters in the frontal lobe were made up of three elements. They were made up of portions of the left orbital-inferior frontal gyrus, which is a key region for language comprehension and production and the right orbital-inferior frontal gyrus. The latter is associated with functions like attention, motor inhibition, imagery, social cognitive processes, and processing speech and language. White matter was the final component of these clusters.

The researchers also found significant differences in the right ventral diencephalon region in the brain. This area is linked to many key bodily functions such as releasing hormones, sending sensory and motor signals to the outer surface of the brain. These functions are responsible for processing thought, emotion, language and memory, and the body's daily sleep and wake cycle. Researchers say that this is the first study that focuses on how the virus affects actual composition of the brain, and how it in turn causes long Covid symptoms.  'Our study highlights this new aspect of the neurological effects of Covid-19 and reports significant abnormalities in Covid survivors,' Ms Mishra said. She added: 'This study points to serious long-term complications that may be caused by the coronavirus, even months after recovery from the infection. 'The present findings are from the small temporal window. However, the longitudinal time points across a couple of years will elucidate if there exists any permanent change.' The researchers are now conducting a study on the same patient cohort to determine whether these brain abnormalities persist over a longer time frame. Long Covid has puzzled scientists and physicians since it first popped on their radar in 2020. Its causes have not been figured out, but experts believe it could be tied to the body's immune response to the virus. There have also been previously known cases of people suffering long-term symptoms after suffering more common viruses like the flu. The CDC estimates that around 7.5 per cent of American adults are suffering from long Covid symptoms. Sufferers are generally under the age of 50, and are more likely to be women. Reports of long Covid are most common in southern states like Kentucky and Alabama. 

SARS-CoV-2, the virus responsible for COVID-19 infects and replicates in astrocytes, reducing neural viability.  A preliminary version (not yet peer-reviewed) posted in 2020 was one of the first to show that the virus that causes COVID-19 can infect brain cells, especially astrocytes. It also broke new ground by describing alterations in the structure of the cortex, the most neuron-rich brain region, even in cases of mild COVID-19. The cerebral cortex is the outer layer of gray matter over the hemispheres. It is the largest site of neural integration in the central nervous system and plays a key role in complex functions such as memory, attention, consciousness, and language. The investigation was conducted by several groups at the State University of Campinas (UNICAMP) and the University of São Paulo (USP). Researchers at the Brazilian Biosciences National Laboratory (LNBio), D’Or Institute (IDOR) and the Federal University of Rio de Janeiro (UFRJ) also contributed to the study. “Two previous studies detected the presence of the novel coronavirus in the brain, but no one knew for sure if it was in the bloodstream, endothelial cells [lining the blood vessels] or nerve cells. We showed for the first time that it does indeed infect and replicate in astrocytes, and that this can reduce neuron viability,” Daniel Martins-de-Souza, one of the leaders of the study, told Agência FAPESP. Martins-de-Souza is a professor at UNICAMP’s Biology Institute and a researcher affiliated with IDOR.

Astrocytes are the most abundant central nervous system cells. Their functions include providing biochemical support and nutrients for neurons; regulating levels of neurotransmitters and other substances that may interfere with neuronal functioning, such as potassium; maintaining the blood-brain barrier that protects the brain from pathogens and toxins; and helping to maintain brain homeostasis. Infection of astrocytes was confirmed by experiments using brain tissue from 26 patients who died of COVID-19. The tissue samples were collected during autopsies conducted using minimally invasive procedures by Alexandre Fabro, a pathologist and professor at the University of São Paulo’s Ribeirão Preto Medical School (FMRP-USP). The analysis was coordinated by Thiago Cunha, also a professor in FMRP-USP and a member of the Center for Research on Inflammatory Diseases (CRID).

The researchers used a technique known as immunohistochemistry, a staining process in which antibodies act as markers of viral antigens or other components of the tissue analyzed. “For example, we can insert one antibody into the sample to turn the astrocytes red on binding to them, another to mark the SARS-CoV-2 spike protein by making it green, and a third to highlight the virus’s double-stranded RNA, which only appears during replication, by turning it magenta,” Martins-de-Souza explained. “When the images produced during the experiment were overlaid, all three colors appeared simultaneously only in astrocytes.” According to Cunha, the presence of the virus was confirmed in five of the 26 samples analyzed. Alterations suggesting possible damage to the central nervous system were also found in these five samples. “We observed signs of necrosis and inflammation, such as edema [swelling caused by a buildup of fluid], neuronal lesions and inflammatory cell infiltrates,” he said. The capacity of SARS-CoV-2 to infect brain tissue and its preference for astrocytes were confirmed by Adriano Sebolella and his group at FMRP-USP using the method of brain-derived slice cultures, an experimental model in which human brain tissue obtained during surgery to treat neurological diseases such as drug-refractory epilepsy, for example, is cultured in vitro and infected with the virus.

Brain scans before and after infection showed more loss of gray matter and tissue damage, mostly in areas related to smell, in people who had Covid than in those who did not.  Covid-19 may cause greater loss of gray matter and tissue damage in the brain than naturally occurs in people who have not been infected with the virus, a large new study found. The study, published Monday in the journal Nature, is believed to be the first involving people who underwent brain scans both before they contracted Covid and months after. Neurological experts who were not involved in the research said it was valuable and unique, but they cautioned that the implications of the changes were unclear and did not necessarily suggest that people might have lasting damage or that the changes might profoundly affect thinking, memory or other functions. The study, involving people aged 51 to 81, found shrinkage and tissue damage primarily in brain areas related to sense of smell; some of those areas are also involved in other brain functions, the researchers said.  “To me, this is pretty convincing evidence that something changes in brains of this overall group of people with Covid,” said Dr. Serena Spudich, chief of neurological infections and global neurology at the Yale School of Medicine, who was not involved in the study.  But, she cautioned: “To make a conclusion that this has some long-term clinical implications for the patients I think is a stretch. We don’t want to scare the public and have them think, ‘Oh, this is proof that everyone’s going to have brain damage and not be able to function.’”

The study involved 785 participants in UK Biobank, a repository of medical and other data from about half a million people in Britain. The participants each underwent two brain scans roughly three years apart, plus some basic cognitive testing. In between their two scans, 401 participants tested positive for the coronavirus, all infected between March 2020 and April 2021.  The other 384 participants formed a control group because they had not been infected with the coronavirus and had similar characteristics to the infected patients in areas like age, sex, medical history and socioeconomic status. With normal aging, people lose a tiny fraction of gray matter each year. For example, in regions related to memory, the typical annual loss is between 0.2 percent and 0.3 percent, the researchers said. But Covid patients in the study — who underwent their second brain scan an average of four and a half months after their infection — lost more than noninfected participants, experiencing between 0.2 percent and 2 percent additional gray matter loss in different brain regions over the three years between scans. They also lost more overall brain volume and showed more tissue damage in certain areas.  “I find it surprising in the sense of how much more was lost and how generalized it is,” said Dr. Spudich, who has studied the neurological effects of Covid. She added, “I wouldn’t have expected to see quite so much percentage change.” The effects may be particularly notable because the study involved mostly people who — like the majority of Covid patients in the general population — were mildly affected by their initial Covid infection, not becoming sick enough to need hospitalization.

The study’s lead author, Gwenaëlle Douaud, a professor in the department of clinical neurosciences at the University of Oxford, said that although the number of hospitalized patients in the study, 15, was too small to yield conclusive data, results suggested that their brain atrophy was worse than the mildly afflicted patients. People who had Covid also showed greater decline than uninfected people on a cognitive test related to attention and efficiency in performing a complex task. But outside experts and Dr. Douaud noted that the cognitive testing was rudimentary, so the study is very limited in what it can say about whether the gray matter loss and tissue damage the Covid patients experienced affected their cognitive skills. “None of them got thorough enough cognitive testing to know if they had significant deficits in these many regions where they found these changes in volume,” said Dr. Benedict Michael, an associate professor of neurological infections at the University of Liverpool, who is researching the neuropsychiatric effects of Covid and was not involved in the study. “We don’t know that it actually means anything for the patient’s quality of life or function.” For example, although some of the largest gray matter loss was in areas related to smell, including the orbitofrontal cortex and parahippocampal gyrus, those areas are also involved in memory and other functions. But the Covid patients did not perform worse than noninfected participants on memory tests, Dr. Douaud said, although she added that the memory tests they took were brief and basic. 

The main cognitive assessment where Covid patients showed a deficit was the trail-making test, a connect-the-dots type of exercise involving alternating letters and numbers. Covid patients took longer to complete the task, which might suggest weaknesses in focus, processing speed and other skills. Dr. Douaud said this diminished ability correlated with loss of gray matter in a specific region of the brain’s cerebellum. But the study doesn’t prove cause and effect, said Dr. Spudich, who also said that the cerebellum, primarily associated with balance, coordination and movement, “is not the first brain structure you think of” to explain changes in ability on the trail-making test. One significant limitation to the study, Dr. Douaud said, is that researchers did not have information about people’s symptoms, including whether they lost their sense of smell. The researchers also could not identify whether any patients had long Covid, so it’s unclear if the findings relate to that long-term condition. Differences between infected and uninfected people increased with age. On the trail-making test, for example, performance was similar in both groups for people in their 50s and early 60s, but the gap widened significantly after that. “I don’t know if that’s because younger people recover faster or they were not as affected to start with,” Dr. Douaud said. “Could be either or it could be both.” Dr. Michael cautioned that the findings could not be extrapolated to the many younger people experiencing post-Covid brain fog and other cognitive issues. And since gray matter and tissue damage were measured at only one time-point after infection, “we don’t know if it’s just a transient change that gets better with recovery,” he said. Outside experts and the study’s authors said the range of brain areas where Covid patients experience more gray matter loss raised intriguing questions....

Study published March 7, 2022 in Nature:

https://doi.org/10.1038/s41586-022-04569-5 

Like a key, SARS-CoV-2—the virus that causes coronavirus disease 2019 (COVID-19) - attaches to specific molecules on the host cell surface, opening gateways into the cell interior. Viral entry into host cells triggers a prodigious immune response. Much of this battle is waged within the lungs, which explains why many patients hospitalized with COVID-19 have severe respiratory symptoms. Respiratory symptoms, however, are only part of the story. Increasing evidence points toward blood vessel inflammation as having a crucial impact on the severity of COVID-19. In addition, anywhere from 30 to 80 percent of patients experience neurological symptoms, including dizziness, headache, nausea, and loss of concentration. These symptoms suggest that SARS-CoV-2 also affects cells of the central nervous system. While there is no evidence yet that the virus invades the brain, new work by scientists at the Lewis Katz School of Medicine at Temple University shows that the spike proteins that extrude from SARS-CoV-2 promote inflammatory responses on the endothelial cells that form the blood-brain barrier. The study, published in the December print issue of the journal Neurobiology of Disease, is the first to show that SARS-CoV-2 spike proteins can cause this barrier to become "leaky," potentially disrupting the delicate neural networks within the brain.

"Previous studies have shown that SARS-CoV-2 infects host cells by using its spike proteins to bind to the angiotensin converting enzyme 2 (ACE2) on the host cell surface," explained Servio H. Ramirez, Ph.D., Professor of Pathology and Laboratory Medicine at the Lewis Katz School of Medicine at Temple University and principal investigator on the new study. ACE2 is expressed on endothelial cells, which form the inner lining of blood vessels, and serves a central role in mediating different functions of the cardiovascular system. According to Dr. Ramirez, "since ACE2 is a major binding target for SARS-CoV-2 in the lungs and vasculature of other organs in the body, tissues that are behind the vasculature, that receive blood from affected vessels, are at risk of damage from the virus." It has been unclear, however, whether ACE2 is also present in the brain vasculature or whether its expression changes in health conditions that worsen COVID-19, such as high blood pressure (hypertension). To find out, the team began by examining postmortem human brain tissue for vascular ACE2 expression, using tissues from individuals without underlying health conditions and from individuals in whom hypertension and dementia had been established. Analyses showed that ACE2 is in fact expressed throughout blood vessels in the frontal cortex of the brain and is significantly increased in the brain vasculature of persons with a history of hypertension or dementia.

The researchers then investigated the effects of the SARS-CoV-2 spike protein on brain endothelial cells in cell culture models. Introduction of the spike protein, particularly a portion designated subunit 1, produced substantial changes in endothelial barrier function that led to declines in barrier integrity. The researchers also uncovered evidence that subunit 2 of the SARS-CoV-2 spike protein can directly impact blood-brain barrier function. "This is of importance because unlike subunit 1, subunit 2 of the spike protein doesn't bind to ACE2, meaning that a breach to the blood-brain barrier could occur in a manner that is independent of ACE2," explained postdoctoral fellow and first author on the new report Tetyana P. Buzhdygan, Ph.D. Dr. Ramirez's team further investigated the effects of SARS-CoV-2 spike proteins on tissue-engineered microfluidic constructs designed to mimic a human brain capillary. "The tissue-engineered microfluidic models allow recapitulation of the 3-D cyto-architecture and mechanical forces caused by fluid movement, which the vasculature is continuously exposed to," said Allison M. Andrews, Ph.D., Assistant Professor in the Department of Pathology & Laboratory Medicine at LKSOM and a co-author on the report. Experiments showed that binding of spike protein subunit 1 increased barrier permeability in the engineered vessel-like constructs. "Our findings support the implication that SARS-CoV-2, or its shed spike proteins circulating in the blood stream, could cause destabilization of the blood-brain barrier in key brain regions," Dr. Ramirez said. "Altered function of this barrier, which normally keeps harmful agents out of the brain, greatly increases the possibility of neuroinvasion by this pathogen, offering an explanation for the neurological manifestations experienced by COVID-19 patients."...

Original study published in Neurobiology of Disease:

https://doi.org/10.1016/j.nbd.2020.105131

SARS-CoV-2 generally attacks the lungs, but researchers are also stressing its effects on the brain in a fraction of patients. Newly described case reports add to growing evidence that COVID-19 infections can result in severe, long-lasting neurological complications—including inflammation, psychosis, delirium, nerve damage, and strokes—even among patients experiencing mild cases of the virus with few other symptoms. In some instances, the new study claims, these neurological effects were the first manifestation of the disease. In a paper published today (July 8) in the journal Brain, neurologists in the UK noted an uptick this spring in cases of a potentially fatal condition called acute disseminated encephalomyelitis (ADEM). While ADEM is usually diagnosed in younger children after a viral infection, researchers at the college’s Institute of Neurology tell The Guardian that they saw two or three cases per week among coronavirus patients during April and May. Ordinarily, the hospital sees about two ADEM cases per month among adults. “We’re seeing things in the way Covid-19 affects the brain that we haven’t seen before with other viruses,” says Michael Zandi, a consulting neurologist at the university’s hospital and the study’s senior author. “What we’ve seen with some of these Adem patients, and in other patients, is you can have severe neurology, you can be quite sick, but actually have trivial lung disease,” he adds.

COVID-19 is primarily a respiratory disease that attacks the lungs, but it has also manifested seemingly unrelated symptoms, such as a loss of taste and smell or memory loss, that can persist for months beyond the initial diagnosis. These oddities suggest a neurological source. The study detailed the neurological symptoms of 43 patients hospitalized in the National Hospital for Neurology and Neurosurgery in London with confirmed or suspected cases of COVID-19. A dozen were diagnosed with inflammation of the central nervous system, including nine cases of ADEM. A further 10 patients experienced delirium or psychosis. Eight patients suffered strokes, including one that was fatal, and another eight had peripheral nerve damage. At least two patients also developed strange behaviors shortly after being discharged from the hospital. One woman, as described in the paper, repeatedly donned and took off her coat, and began hallucinating lions and monkeys inside her home. Another woman became drowsy and ultimately needed emergency surgery to relieve the pressure on her brain...

For three months, Chelsea Alionar has struggled with fevers, headaches, dizziness and a brain fog so intense it feels like early dementia. She came down with the worst headache of her life on March 9, then lost her sense of taste and smell. She eventually tested positive for the coronavirus. But her symptoms have been stranger, and lasted longer, than most. “I tell the same stories repeatedly; I forget words I know,” she told me. Her fingers and toes have been numb, her vision blurry and her fatigue severe. The 37-year-old is a one of the more than 4,000 members of a Facebook support group for Covid survivors who have been ill for more than 80 days.

The more we learn about the coronavirus, the more we realize it’s not just a respiratory infection. The virus can ravage many of the body’s major organ systems, including the brain and central nervous system. Among patients hospitalized for Covid-19 in Wuhan, China, more than a third experienced nervous system symptoms, including seizures and impaired consciousness. Earlier this month, French researchers reported that 84 percent of Covid patients who had been admitted to the I.C.U. experienced neurological problems, and that 33 percent continued to act confused and disoriented when they were discharged.

According to Dr. Mady Hornig, a psychiatrist and epidemiologist at the Columbia University Mailman School of Public Health, the possibility that neurological issues “will persist and create disability, or difficulties, for individuals downstream is really looking more and more likely.” Infections have long been implicated in neurological diseases. Syphilis and H.I.V. can induce dementia. Zika is known to invade developing brains and limit their growth, while untreated Lyme disease can cause nerve pain, facial palsy and spinal cord inflammation. One man with SARS developed delirium that progressed into coma, and was found to have the virus in his brain tissue after his death.