The mysteries of Covid-19

First, here’s a pretty cool video that packs a ton of information about the disease of Covid-19 into about 5 minutes.

One of the things I find so interesting about the disease is all the stuff we don’t know.  We have a pretty good scientific understanding of why people with heart problems, or lung problems, or weakened immunity (all of which are notably more common in older people, of course) are much more likely to get a severe or fatal case.  But, I keep hearing these stories of “otherwise healthy, regular-exercising 48 year old” that, for obvious reasons, kind of scare me to death.  Yes, the incidence of these severe and fatal cases in people with literally none of the risk factors is low, but it is decidedly not zero.  For example, in Spain, 14% of twenty-somethings were hospitalized (good Vox piece on the age breakdowns).

So, what’s going on?  Nobody really knows yet.  Also, very interesting is the latest finding that many sufferers seem to be losing their sense of taste/smell.  Would be great to get some good numbers on the prevalence of that.  Especially because, unlike headache, fatigue, cough, etc., which are so common in a variety of diseases if you suddenly lose your sense of smell right now, that’s almost surely got to be Covid.  My first local friend that I know of with the disease said that this was his most notable symptom, along with headache, and that he never even had a fever.  Also, for the record, he got tested because the person he caught it from warned him to get tested.  They had apparently shared “…just your normal dinner and drinks type of social contact. Handshake and a hug.”  Score one for the evidence of social distancing working to stop transmissions.

And, Ed Yong with a great piece at Atlantic about what we do understand (some) and don’t understand (a lot) about Covid-19 (also, let me make another plug for an Atlantic subscription being so worth the money):

But much about coronaviruses is still unclear. Susan Weiss, of the University of Pennsylvania, has been studying them for about 40 years. She says that in the early days, only a few dozen scientists shared her interest—and those numbers swelled only slightly after the SARS epidemic of 2002. “Until then people looked at us as a backward field with not a lot of importance to human health,” she says. But with the emergence of SARS-CoV-2—the cause of the COVID-19 disease—no one is likely to repeat that mistake again.

To be clear, SARS-CoV-2 is not the flu. It causes a disease with different symptoms, spreads and kills more readily, and belongs to a completely different family of viruses. This family, the coronaviruses, includes just six other members that infect humans. Four of them—OC43, HKU1, NL63, and 229E—have been gently annoying humans for more than a century, causing a third of common colds. The other two—MERS and SARS (or “SARS-classic,” as some virologists have started calling it)—both cause far more severe disease. Why was this seventh coronavirus the one to go pandemic? Suddenly, what we do know about coronaviruses becomes a matter of international concern…

For example, most respiratory viruses tend to infect either the upper or lower airways. In general, an upper-respiratory infection spreads more easily, but tends to be milder, while a lower-respiratory infection is harder to transmit, but is more severe. SARS-CoV-2 seems to infect both upper and lower airways, perhaps because it can exploit the ubiquitous furin. This double whammy could also conceivably explain why the virus can spread between people before symptoms show up—a trait that has made it so difficult to control. Perhaps it transmits while still confined to the upper airways, before making its way deeper and causing severe symptoms. All of this is plausible but totally hypothetical; the virus was only discovered in January, and most of its biology is still a mystery…

The new virus certainly seems to be effective at infecting humans, despite its animal origins. The closest wild relative of SARS-CoV-2 is found in bats, which suggests it originated in a bat, then jumped to humans either directly or through another species. (Another coronavirus found in wild pangolins also resembles SARS-CoV-2, but only in the small part of the spike that recognizes ACE2; the two viruses are otherwise dissimilar, and pangolins are unlikely to be the original reservoir of the new virus.) When SARS-classic first made this leap, a brief period of mutation was necessary for it to recognize ACE2 well. But SARS-CoV-2 could do that from day one. “It had already found its best way of being a [human] virus,” says Matthew Frieman of the University of Maryland School of Medicine.

This uncanny fit will doubtlessly encourage conspiracy theorists: What are the odds that a random bat virus had exactly the right combination of traits to effectively infect human cells from the get-go, and then jump into an unsuspecting person? “Very low,” Andersen says, “but there are millions or billions of these viruses out there. These viruses are so prevalent that things that are really unlikely to happen sometimes do.”…

But why do some people with COVID-19 get incredibly sick, while others escape with mild or nonexistent symptoms? Age is a factor. Elderly people are at risk of more severe infections possibly because their immune system can’t mount an effective initial defense, while children are less affected because their immune system is less likely to progress to a cytokine storm. But other factors—a person’s genes, the vagaries of their immune system, the amount of virus they’re exposed to, the other microbes in their bodies—might play a role too. In general, “it’s a mystery why some people have mild disease, even within the same age group,” Iwasaki says. [emphasis mine]…

“The scary part is we don’t even know how many people get normal coronaviruses every year,” Frieman says. “We don’t have any surveillance networks for coronaviruses like [we do for] flu. We don’t know why they go away in the winter, or where they go. We don’t know how these viruses mutate year on year.” Until now, research has been slow. Ironically, a triennial conference in which the world’s coronavirus experts would have met in a small Dutch village in May has been postponed because of the coronavirus pandemic.

“If we don’t learn from this pandemic that we need to understand these viruses more, then we’re very, very bad at this,” Frieman says.

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