However, symptoms such as fatigue are often not recognized as being associated with myocarditis. And dr. McManus speculates that the fatigue that sometimes follows a battle with Covid-19 could be caused by this heart problem.
"We view Covid-19 and influenza as respiratory diseases, and indeed they are," said Dr. Bruce M. McManus, Professor Emeritus of Pathology at the University of British Columbia. "But the reason many patients die in many cases is because of the myocardium."
Some seriously ill Covid patients have lung damage. That can also happen with other viruses, said Dr. Clemente Britto-Leon, lung researcher at the Yale School of Medicine. He lists a few possibilities.
"You can have lung injuries and scars with influenza, herpes viruses, and cytomegalovirus infections," said Dr. Britto, referring to a common virus that usually doesn't cause symptoms. All of these viruses can, on rare occasions, cause harm, he said. "You can have a very serious injury and a lot of tissue damage."
Influenza can cause blood clots in the lining of the lungs that look just like the small blood clots in the lungs of some Covid patients, said Marco Goeijenbier of Erasmus University in the Netherlands. It happens when flu viruses infect the lower respiratory tract, an unusual occurrence since most people already have protective immunity.
Dr. Goeijenbier wants to examine the blood clots that occur in these cases. So far, he and others have reproduced and examined the effects in so few patients in laboratory studies and in ferrets – the animals of choice for studying the flu.
“It was hard to get money, he said. "Big magazines or funders didn't think that was interesting enough," he said.
Covid changes that.
There is now "a huge cohort of people to study," said Pamela Dalton, a olfactory researcher at Monell. But "the big question, even if you learn all about SARS-CoV-2" – the formal name of the coronavirus – is "how generalizable is it?"