Scientific American:

The new coronavirus that has infected millions of people around the globe can wreak havoc far beyond the lungs. Some of the symptoms of the disease it causes, COVID-19, are predictable enough: cough, fever, chills, headache. But the pathogen’s effects by no means stop there. The virus can cause problems in almost every organ, including the brain, heart, kidneys, gastrointestinal tract and skin.

Physicians have been taken aback at what they now call silent hypoxia, or happy hypoxia, a phenomenon in which people with dangerously low levels of blood oxygen are astonishingly not struggling to breathe. And there is “COVID toe,” painful swellings on the skin called chilblains. In rare cases, children—who were previously thought to be relatively spared from severe illness—come down with symptoms akin to Kawasaki disease, which leads to inflamed blood vessels throughout the body. Complications associated with blood clots, such as strokes and pulmonary embolisms (blockages of blood vessels in the lungs) also turn up. “It’s interesting that a respiratory virus will cause such a diverse array of clinical sequelae,” says Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.

One of the reasons for the unusual manifestations of COVID-19 may simply be the more than four million confirmed cases worldwide of a wholly new illness. Some of these symptoms have appeared during other viral infections—for example, researchers have seen blood clots in some patients infected with the original SARS coronavirus and the H1N1 influenza virus. “There are so many cases in the world now that we may be picking up on minor variants,” says Stanley Perlman, a professor of microbiology and immunology at the University of Iowa. “It makes you wonder, if in other infections, you look at two [million] to three million [cases], how many of these kinds of events would occur. Or is [the situation] really special for COVID-19?”

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