COVID-19's Effects on the Brain | Global Watch | Dr. Sean Lin

Hello everyone, welcome to Global Health Watch. This is Dr. Sean Lin. COVID-19 has been spreading around globally for the last almost 13 months right now. And still a lot of people in their own perception, the COVID-19 primarily brings respiratory distress in patients. People always think, oh, because this virus primarily transmitted through aerosols. As people inhale the virus or maybe through contact, the virus primarily causing respiratory distress and you got severe infection in the lung for patients who develop symptoms for the COVID-19. So most people think of the virus primary target, my respiratory tract, you know, whether upper respiratory tract or lower or in the lung system. And you can see people die from hard to breathing, you know, very, very painful process. And some people will even drop on the street and when they have a very hard time to catch the breathing. So this is a common perception, but today I wanna talk about the virus infecting the central nervous system. Because in the past, you know, a lot of patients say, after the COVID infection, I've lost my sense, the capability to smell things, to taste things, right? So this actually indicating the virus can interfere with your nerve systems and maybe even infecting the brain. But most of the time people just think these are minor symptoms, this is not severe. But today I wanna present interesting study just recently conducted by Georgia State University. They talk about the virus maybe even hiding human brain. So let me talk about these research. And of course, I will give you some background regarding other coronavirus so that you don't feel this is some isolated situation. So maybe this topic's a little bit too academic, but I'll try to explain it in a simple term, hope everybody can understand. All right, let's look at some of the slide that I prepared. So first, I wanna bring you to attention to one of the study in last April. And this was published on JAMA, that's a Journal of American Medical Association, and that was in last April. And this study was conducted by a group of Chinese scientists in Wuhan, you know, the Wuhan city where is the epicenter for the initial outbreak of the COVID-19. So this was a group of doctors in hospitals in Wuhan, they collected many patient samples, and those samples are from patients who developed neurological symptoms, and they collected about 214 patients. So they collected these more than 200 patient samples and many of these patients, because they still developing symptom at a time, so they cannot do too much cross examinations and getting biopsy samples. So a lot of the results were collected through their oral investigation with the patients and rely on patients telling their symptoms, especially, you know, maybe some minor neurological symptoms like nausea, dizziness, fatigue, these kind of situations. So, and they also relied on a lot of these electronic medical records that was collected after the patient was released from the hospital. So, of course, the data is collected was limited, but it's very important study because this is the first study after the COVID outbreak that focus on the neurological symptoms. So this data of all neurologic symptoms were also reviewed and checked by two trained neurologists, and they categorized the neurological manifestation into three categories. The one is in central nervous systems, so including dizziness, headache, and impaired consciousness and acute cerebrovascular disease and atesia and seizures. And then second category is peripheral nervous systems. So these manifestation include taste impairment, smell impairment, that's what I talk about. You lost your taste capability, you cannot smell things. And then vision impairment, some people cannot even see clearly. And then the third category is skeletal muscular injury. And so these are the three main category they study in this study. So what did they find? So from the 214 patients, they found out 126 patients, so about 59% of the patients had non-severe infection and 88 patients had severe infection. So among all these patients, 78 patients, that means 36.4% had neurological manifestation. So keep this number in mind because this is very high number of showing neurological manifestation because most of the time people don't think COVID-19 or the SARS-CoV-2, the virus, is neurotropic. Neurotropic means the virus specific targeting to your neural system, right? So like a rabies virus, we know it's a specific neurotropic virus. But with the SARS-MERS and the SARS-CoV-2, nobody think it's neurotropic. But the percentage of 36.4% is really high. That means the virus infecting the neural system is actually one of the important pathway that is spread out in the human body. I just, these number is actually quite alarming. I think this is alarming data for every neurologist, even to virologists too, right? So let's look more about this data. So another finding is that compared with patients with non-severe infection, patients with severe infection were older and they had more underlying disorders, especially hypertensions. And they show fewer typical symptoms of COVID-19 such as fever and cough. And the most important finding is that the patient with more severe infection had neurological manifestation such as acute cerebrovascular disease and that's five cases versus one. One is the one people don't show in non-severe infection. And then impaired consciousness. So there's 13 cases versus three cases. And skeletal muscular injuries, there's 17 cases versus six cases, right? So the conclusion from these studies suggesting that a patient with COVID-19 commonly have neurological manifestation. So this is one important conclusion. And then another important observation is that during the epidemic period of COVID-19, when seeing patients with neurological manifestations, clinicians should suspect SARS-CoV-2 infection as a differential diagnosis to avoid delayed diagnosis or misdiagnosis or lose the chance to treat and prevent further transmission. Of course, this is a long sentence. So what does it mean exactly? So this basically suggesting if you see people showing COVID-19 symptoms and then people also showing neurological symptoms, if these two situation match together, that's suggesting this patient may have severe infection of COVID-19, right? So this is actually important clinical suggestions. So for the doctors, if you see patients even maybe just showing minor respiratory symptoms, but at the same time, the patient already developed neurological symptoms like losing smell, losing taste capabilities, then suggesting maybe this patient was actually in a severe infection and the virus may already enter his nerve systems, right? So that's suggesting the patient's virus titer in his serums, in his respiratory tract may not show you the full picture of this patient's whole infection situation. So that's why I think this suggestion is very important. So the next question people will naturally ask, so this is for SARS-CoV-2, right? This is new, novel coronavirus, but what about other coronavirus? People know it for a long time, like for example, the SARS, right? There was outbreak in 2003. People find SARS or even MERS, the Middle East Respiratory Syndrome virus, did those virus also attacking people's central nerve systems, right? So let's look at another study here. So this was a very early study I did go, this was actually published in 2003. So detection of SARS coronavirus RNA in this cerebrospinal fluid, CSF, CSF, quite often we just call it CSF, right? Of a patient with severe acute respiratory symptoms. And this was published in Clinical Chemistry, right? That's in 2003. So this one study actually described a SARS patient who developed respiratory failure and the status of epilepticus several days after mounting a fever. And then they identified SARS-CoV's RNA in her CSF, this cerebrospinal fluid, suggesting a demyelinating disease process. So this is one early study, even though it's just one patient study, but it's suggesting virus can enter the brain and you can even find the virus RNA in the CSF. So this was an early study and it didn't mention about identified virus proteins. The primary was identified virus RNA because only finding virus RNA did not tell you full story, right? Maybe the virus has very small amount of virus in the CSF, but if you can detect virus protein, that means the virus is or were actively propagating inside the CSF. So that's a different story, but at least these initial study tell you the virus can enter the brain. So next, another study was talking about possible central nervous system infection by SARS coronavirus. So this is another study done by a Hong Kong group. So the last study I just mentioned was also done by a Hong Kong scientist. So this one is another one from Hong Kong. So this one described a pregnant woman who suffered from generalized tonic and chronic seizures on day 22 of SARS infection. And when they conducting RT-PCR, RT-PCR is a reverse transcriptase, PCR is polyclonal chain reaction, right? Polymerase chain reaction. So RT-PCR is a common technique to identify the virus RNA. So when they're using this technology to check on the SARS-CoV in the CSF, and if they did identify the virus RNA, and even though the CSS parameter were normal, normal cerebral spinal fluid conditions, and then no focal neurological deficits was observed. So that means the virus can enter the CSF, but it probably was not causing severe inflammation in the escalation. So the CSF parameters were normal. So this is another study. So that indicating probably the virus can enter the CSF, but this may not be a virus major route into the central nervous system because the virus was not actively propagating. It didn't cause major inflammations in there. So it is interesting to know that coronavirus has been implicated in this demyelinating brain pathologies. And other study also documented the presence of seemingly harmless human respiratory coronavirus, the OC43 in the brain parenchyma of patient with multiple sclerosis. Also another virus, the murine hepatitis virus is another coronavirus, has been linked to chronic inflammation and demyelination of the central nervous systems. So they're basically suggesting the SARS-CoV infection of brain is definitely a distinct possibility because it can enter the CSF, it can cause the demyelination of the CNS, right? So these previous study, early study of this SARS-CoV suggesting this possibility. And similarly, people were asked about MERS, right? So similar story was found in MERS. And also MERS patients have appeared to showing, developing neurological symptoms. And one of the early studies in 2014, when they study Saudi Arabia's cohort, they actually find six out of 70 patients, so that's about 8.6% people develop seizures. And another study also found the MERS patients with severe neurological symptoms. And so these patients have these altered consciousness, or maybe you can say impaired consciousness, and people were even in coma, atasia, and focal motor deficit. So focal motor deficit probably means there are skeletal muscular injuries. And when they do MRI studies, the image shows the non-enhancing bilateral hyper-intense lesion in white matters, so that's in brain, in white matters, and in subcortical regions of the frontal, temporal, or parietal lobes. So this meaning different part of the brain can be infected by MERS. So basically you can see, for SARS and MERS, all these very severe coronavirus infection can have infection in different part of the brain. But how exactly these SARS-CoV and MERS-CoV, or even SARS-CoV-2 enter the CNS is still not fully understand yet. But people suggesting different route, right? So one route is hematogenous, or lymphatic route seems impossible, especially in early stage of infection, because most of the time, people think the virus goes through the respiratory tract, right, enter your lung. So in early infection for the virus to break through the blood-brain barrier is probably impossible at early stage. And people didn't find any virus particles in the non-neuronal cells in the infected brain areas. So that means that route is not likely, but you cannot totally rule out. But at the same time, increasing evidence show that coronavirus may first invade peripheral nerve terminals and then gain access to CNS via a synapse-connected route. So that's very interesting. The virus may be very smart. It can attack from the peripheral first and then enter your central nerve systems. So in here, we wanna talk about two example. One is hepatitis E virus, 67, and also avian bronchitis virus. So these two type of virus also can enter through peripheral central nerve systems. So the hepatitis E virus, HEV-67, is also a coronavirus, right? So it can invade the person's brain and it shows 91% homology with human coronavirus, OC43. The OC43 is one of the four popular, like I use the word popular, probably say common coronavirus that's circulating in human societies for decades. So this HEV can infect the nasal mucosal, tonsil, lung, and then small intestines and in the suckling piglets. And then they can deliver retrogradually via peripheral nerves to the medulla neurons. So I'll talk about medulla neurons later. I actually have a picture to show you. So just to show you this example, the HEV can enter through this peripheral route. And then, very interesting to see, the virus antigen has been detected in the brainstem in these experiments. And so the infected regions, including the nucleus of the solitary tract and nucleus ambiguous. And the nucleus of solitary tract receives sensory information from the mechanoreceptors and chemoreceptors in the lung and respiratory tract. So these examples showing the hepatitis E virus can enter the central nerve system by first infecting the peripheral nerve systems and then retrogradually infecting the central nerve systems. So next, we wanna talk about, because we talk about the HEVs, we talk about the SARS, talk about the MERS coronavirus. So overall, people start to realize the possibility of central neurological respiratory failure in a setting of coronavirus infections has many potential now. So people put these kind of theory into animal study. They wanna test these theories in animal too. And in 2008, one group using transgenic mice, they expressed humanized angiotensin-converting enzyme too, that's the ACE2 receptor. By today, probably a lot of people get familiar with the term ACE2. That's the receptor for the SARS-CoV-2. And it's also the receptor for SARS-CoV as well. So when people are using transgenic mice, they can put this human receptor on the mice because regular mice will have the murine version of the receptor. So the virus spike protein, whether it's SARS-CoV or SARS-CoV-2 do not bind to murine ACE2 well. So that's why for transgenic mice, so they use the human ACE2 to make it expressed in these mice. So it become a model that you can test in the SARS-CoV or SARS-CoV-2 infection in animal model. So there's one concept I wanna explain. And so they established the model and then found out that you can efficiently using these animal model to study COVID infection because you can identify the virus particles in infections of these transgenic mice. And so the infection in these transgenic mice show the pattern can be thoroughly studied. And they found out that the infection propagated from the sinus to the olfactory bulb. And I will also show a picture later about this olfactory bulb, where they located. And so once the infection of the olfactory bulb was established, the infection spread throughout the brain to reach the medullary respiratory center. So consequently, these mice die from central respiratory failure. And very interestingly, the lungs of the mice show minimal pathological changes. And the initial concentration of ACE2 receptor in brain tissue was only 1% of their concentration in lung tissues. So in this experiment, established infection of the sinuses may have been essential because heptogenous spread to the brain is unlikely. Right, this is, sorry, I'm reading this statement because I have to explain it in a simple term, right? They're suggesting, even for the in this mice model, having a sinus infection may be actually a very bad sign, because if you regularly catch a cold, you think, oh, just a sinus conjecture. That may be a minor symptom. I don't care about it, right? So but this animal study showing you, you have sinus infection. There's a potential the virus can, through this infection in the sinus, infecting your olfactory bulb, and then your medulla in your brainstem area can also be infected. So that's actually a very dangerous route. So they're suggesting we need to wear a face mask better, protect your sinus, protect your nose. So anyway, so this actually, if I explain it in a simple term. So let's look at another slide here. So let me show you some diagram to explain it better. So, right, so this is a diagram for our cerebellums. So the last one I want to mention is actually in the brainstem area, right? So in the brainstem area, and you have the medullary respiratory center there. And this is actually one important thing people need to understand, because most of the time, your cardiovascular system, your heartbeat is spontaneous, it's on control, right? But when you're doing exercise, and so your brain can involve in regulating your breathing in your heartbeat. And so in your brainstem area, so you have this respiratory center, and the respiratory center exists in the medulla and also in the pons. And so these are very important area that can cause in your, if it malfunction, it can make people loss of capability to breathe and stop your heartbeat as well. And so further explain the human olfactory system. So you can see here probably better, right behind your nose, the sinus, and you connect it to olfactory bulb, that's depicted as number one in here. And there's a zooming picture in the middle. And you can see these olfactories also have mitral cells, and they also have glomerulus, and then in their areas, it can also have the bone structure as well as these olfactory receptor neurons. So that's how it works, right? Because when you hear about the name olfactory, you only think about your smelling system, maybe your system to make you smell things, right? You don't think it's connected to your brain through such a very dedicated mechanisms. So the olfactory receptor neurons provide a channel, the virus can, when it infected the olfactory bulb, it can further infect olfactory receptor neurons, and then from there, it can go deeper into medulla in your brainstem. So recently, I wanna mention at the beginning, I mentioned about I wanna bring you attention to one of the most recent studies. So this one study is actually conducted by scientists in the Department of Biology at Georgia State University. And they also using these transgenic mice models, and they actually documented, or you can say they find some evidence about neural invasions and following the intranasal inoculation of SARS-CoV-2 in these transgenic mice. So let me show you some of their datas. So these figures shows the analysts of the survival and the body weight as well as the virus titles in these transgenic mice following the SARS-CoV-2 infection. So basically, they inoculate this virus through the intranasal pathways, and then they monitor the transgenic mice on day zero, day two, four, six, and eight. And on this diagram, you can see the panel A shows the virus survival situation, and pretty much by day six, all of them die. And then the body weight loss, you can see very clearly the percentage of weight loss for the mice receiving the SARS-CoV-2 inoculation have significant weight loss before they pass away. And then panel C shows the lung conditions, and there's a plaque showing the virus spreading in the lungs and the RT-PCR showing the virus titles. And you can see virus titles peak at day three, and then on day six, it dropped a little bit, but still significant. The virus title is still up to 10 to fifth, right, genome copies per micrograms of RNA. And then you can see in the brain, very interestingly, in brain on day five and day six, the virus title, the RNA virus title, that's plaque assay, that's in panel E, and then panel F showing the RT-PCR result, so that's virus RNA. So both virus title as well as virus RNA title all very high on day five and day six, while in the lung, the virus title and virus RNA title already start to drop in day six. So very interesting. So virus can clear from your respiratory tract from your lung, but it still has a high title in the brain. So that's very important observation. And the next figure, they further analyze the virus tropism in different organs. So in here, it has several panels. So they studied about nasoturbinates, olfactory bulbs. So you remember, we just mentioned about olfactory bulbs. So you can see the title of the virus increase from day three, and then day five, and day six. The virus will amplify pretty high. This is a small figure, but you can see from the y-axis. So when they inoculate about 10 to 15 virus particle on the day one, by day six, the virus titles reach almost 10 to nine, 10 to nine. So that's about 10,000 fold increase of virus title. So it's pretty high. And same in the eye, and the title is not that high in eye, but you can see that you need to pay attention to the y-axis, right? So the virus title in the eyes is about 10 to six in the maximum on the day six, but in the olfactory bulb, the virus title is almost 10 to nine. So that's 1,000 fold higher than in the eyes. And the virus replicate poorly in the serum when you inoculate the virus in the intranasal pathways. And not much change in the kidney, and spleen, liver, heart, pancreas. The virus titles pretty much just maintain about 10 to face level. So most amazing increase is actually in olfactory bulb. So that's a very important observation. And next figure, we just kind of show you more visually in these staining experiments. So basically, you have three panels, right? Vertical panels, three panels. And the far left one show you the nuclei, the means to just tell you the cells there in staining. And the mark one is when they inoculate the mice with PBS buffer, no virus. So you didn't see any staining. And the last panel on the right is when you inoculate the SARS-CoV-2 into the mice. And then you can detect the S protein, the spike proteins. So these immunostainings, you can identify these virus protein. So remember, this is virus protein detection, not detecting virus RNA. So when you can detect proteins, the virus replicate efficiently in these areas. So they can detect these S proteins in the cortex, in the cerebellums, in the olfactory bulb, as well in hippocampus, right? So higher expression seems to be in the cortex and cerebrums and olfactory bulb. In hippocampus, it was very small volumes of propagation of the virus. But this is just staining. It's not quantitative, but just kind of indicative of the virus replication capability in these different organs, different tissues. So the last figure I wanna show you, this is actually histological stainings. So this is analyzing the SARS-CoV-2 infected mice for their different brain sections. And so these panel A and panel B showing the hematocycline and eosin staining. And so the top arrow is for the mark when the mice were inoculated with PBS. And then the second panel is for mice is inoculated with the virus. And last panel, last arrow was some zooming about those box region from the second row. So then you can see on the third column is a CD45 and your new N markers. So CD45 is leukocyte markers. New N is a neuronal markers. So you can see for mark, basically there's no highlighted red stainings and green stainings, right? So red staining means you have leukocyte markers there. And when you have the green dots there, it means you have neuronal markers there. And so you can see a lot higher leukocyte markers in the second row and the solid columns, right? So it means there's severe symptoms developed in these SARS-CoV-2 infected mice. And when you're using tunnel assay, in tunnel assay basically identify apoptotic cells. So you can see on the second row, on the last columns, a lot of cells turn into apoptic situation. That means cell is on the programmed test, the cells dying because of the infection, right? So this showing virus infection is not just like latent infection didn't cause pathological effect. So definitely this showing the virus infection causing these brain tissues dying with so many cells into cell programmed test. So anyway, this is one of the recent studies showing you a very interesting observation in this transgenic mice model. And because of the time constraint in the program, did not want to talk more about more studies. And, but today I'm probably just focused on these transgenic mice model study. But it's very interesting in mice models, relatively easier to do different autopsies. And if you have, sometimes it's very hard to do autopsy studies for COVID-19 infected patients. So in this mice model, you see more clearly the virus infecting different part of the nerve system, right? From the olfactory bulbs to medullas and to cortex and to different part of the brain. So I think I want to highlight that this study actually suggesting a very important mechanism maybe the virus is using. Because you can see the virus can be clear from your respiratory systems, from your lung, from your respiratory tracts. And people feel they can breathe better, they probably can feel better as a patient. But at the same time, the virus can still replicate whether it's replicate very accurately in your central nerve system or maybe can just in latent status in your brain system. Maybe the virus was hiding in your brain because when the virus hiding in the brain, your immune systems, right? Through your B cell, T cells, right? It's hard to reach the brain. So the virus can hide in there for maybe for a long time when waiting there and you feel you recovered. But when one day when your immune system is weaker, maybe you have a certain period of time you were totally exhausted, you had a other infection, your immune system drop its capability. Then the virus can surge out from your brain and then passing out to your other part of the body. So there may be a very important mechanisms, right? So I think this study is suggesting a very important maybe an evasion mechanism or strategies the virus can use. The virus primarily infecting your respiratory systems and of course, renal system also got infected, different part of the organ can be infected. But people may not pay attention to the virus infection in your brain. It can be a reservoir, the virus just store itself there, hide itself there. When it's needed, the virus can propagate actively and then people will be in a terrible situation because if your olfactory bulb got infected and then pass to the medulla and then your medulla respiratory center got infected, then people can have difficulty in breathing, may further trigger heart attack. And that may be another reason that can explain some people just walk on the street, feels relatively okay but suddenly they may be drop dead, right? Because if your brain stem got infected and especially the medulla respiratory center got infected, you will suddenly have, when you reach a threshold, suddenly you will have difficulty in breathing. And so that may be a very dangerous route, the virus can harm people. So anyway, these studies suggest this potential and maybe in my future episode, if I have time, I can talk more about human cases, human studies and suggesting the virus actually can attack human central nerve system from different route. Because today we mentioned several routes, right? From olfactory bulb to medullas to your respiratory centers in the brain stems, that's one route. And then they can also through other periphery nerve systems through retrograde systems to enter your brain and maybe even through demyelinating process to damage your brain. There are several routes the virus can attack the brain. So one key issue is whether the virus can effectively using receptors in the brain or in the central nerve system. We know relatively the ACE2 receptors express a lower quantities on the central nerve system, but not all central nervous systems tissues express same low level ACE2. And so these all warrant more studies on these critical issues in helping us to understand how these SARS-CoV-2 can lead to more, can become more pathogenic, right? So this is also a very, very important area that people need to monitor how the virus may be using different receptors in the central nerve system. Maybe they find additional paths through the different mutation, they can enter the central nervous system more efficiently. So I think this is also an alert and I want to put out in advance. All right, I've been talking a while on this topic. Hope I can, I did explain it somewhat easier for you to understand. And if you are interested in this topic, you are welcome to leave some comments and notes under my programs on YouTube. And well, thank you for watching today's program. And I will bring you more information about the COVID-19, about the pandemic situation in my future programs too. And thank you for watching. If you like my program, welcome to subscribe and click like. All right, this is Dr. Sean Lin. Thank you for watching. See you next time.