Over and over again, we hear the counter argument to concerns over Covid-19: That the death rate is exaggerated. That the total known infections skew the fatality rate, because many people never had symptoms and never were tested. That it's only the very old who die.
As of the latest tally of over 5 million known infections in the U.S. as of Sunday, some 162,000 have died. To put this in perspective, for every 100 people who get diagnosed with an infection, around three will not survive.
But the narrow focus on Covid-19 fatalities distracts from the growing evidence of the potentially devastating toll the novel coronavirus can have on patients’ bodies. Far more than the number of infected people who will die will be hospitalized for weeks or more. Some of those severely hit patients will suffer from what's known vaguely as "cytokine storm syndrome" -- a kind of hyper-inflammatory response that is believed to often lead to death.
Previously healthy patients are also increasingly let out of the hospital only to find they have hearts that are damaged. Some people report lingering loss of smell or taste or hair that’s falling out after “recovering.”
Now a study published in the journal “Cell Research” appears to further shed light on the harm the virus can unleash on the body, revealing the possibility that it can affect the human nervous system and brain.
The work could explain why some patients infected with SARS-CoV-2 – the virus that causes Covid-19 – have lost their sense of smell and taste and have shown signs of delirium, suggests the research from the University of Hong Kong’s school of medicine, where professors conducted the study that in part relied on research of hamsters. The work concluded that its findings “suggest that the human brain might be an extra-pulmonary target of SARS-CoV-2 infection.”
This is perhaps no surprise, as other coronaviruses can also affect the brain and nervous system, too, said Jiandong Huang, a professor at the School of Biomedical Sciences at the University of Hong Hong's medical school, who worked on the study.
“The literature has documented that other coronaviruses also target the central nervous system and cause changes in the nervous system, including brain inflammation and encephalomyelitis,” which is a type of inflammation of the brain and spinal cord, said Huang.
Some coronaviruses have been associated with fatal childhood encephalitis, he said, and some patients of SARS -- another disease caused by a similar coronavirus -- had particles of the virus present in their brain. “These particles are almost entirely located in neurons,” Huang said, adding that more study of coronaviruses – including the one causing Covid-19 – “are urgently needed."
TheStreet interviewed Huang this week by email. Below is a lightly edited version of the interview.
TheStreet: Loss of smell and loss of taste as well as delirium have been anecdotally documented, and now it seems your work shows it's possible these are caused by the virus' ability to affect the brain. Correct?
Huang: Neurological manifestations in Covid-19 cases were frequently reported, but the underlying mechanism that resulted in these symptoms are not known. Previous studies suggested that these central nervous system symptoms could be a result of the inflammatory cytokines triggered by the virus. The loss of smell and loss of taste could be a result of topical inflammation at the nasal cavity or a result of virus infection of the olfactory sensory neurons.
Now, our study reveals another possible explanation of these neurological symptoms, which is direct virus infection of the neural system. The exact locations of the affected neural system responsible for the symptoms remain to be determined for human patients. It may be in the brain or the peripheral regions. As for the loss of smell in hamsters, Prof. Kwok-yung Yuen at the University of Hong Kong showed that the olfactory sensory neurons, their less mature precursors, and the substenacular cells, which are supporting cells of these neurons, are all infected and killed by this virus, accounting for the loss of smell.
TheStreet: Some in the U.S. still compare this virus to influenza, or the common flu, but it seems this is more evidence this is potentially a disease affecting the entire body. Would you agree?
Huang: Yes, I agree. It is now clear that SARS-CoV-2 can affect many organs in humans, such as lungs, kidneys and the neural system. The flu and Covid-19 are both contagious respiratory illnesses, but they are caused by different viruses. Although some of the symptoms of flu and Covid-19 are similar, Covid-19 is more contagious among certain populations and age groups than the flu. Also, Covid-19 has been observed to have more super-spreading events than the flu. This means the virus that causes Covid-19 can quickly and easily spread to a lot of people and result in continuous spreading among people as time progresses.
Globally, about 3.4% of reported Covid-19 cases have died (even though many patients were not diagnosed and that the mortality should be around 1% if taken into account those not diagnosed). By comparison, seasonal flu generally kills far fewer than 1% of those infected.
TheStreet: You compare this to Zika in a way, could you explain? Do you fear long-term neurological harm in some patients?
Huang: Zika virus is well recognized to cause severe birth defects, especially microcephaly in newborns by infecting human neural progenitors and impairing brain development. In our study, we found SARS-CoV-2 could target the neuronal progenitor cell population. Therefore, the chronic or long-term consequence of SARS-CoV-2 infection to the central nervous system should be closely monitored.
TheStreet: Do you believe that this type of finding underscores the need to control Covid-19, as we are still getting a grasp on the potential devastating effects on patients?
Huang: Yes. In the case that the pathogenic mechanism of SARS-CoV-2 is not very clear, and there is no vaccine, it is necessary to pay close attention for the consequences of Covid-19 in recovered patients.