WASHINGTON (NYTIMES) - Ms Barie Carmichael lost her sense of taste and smell while travelling in Europe. She remembers keeping a dinner date at a Michelin-starred restaurant but tasting nothing.

It may sound like a case of Covid-19. But Ms Carmichael, 72, a fellow at the University of Virginia's business school, lost her ability to taste and smell for three years in the 1990s. The only respiratory infection she had at that time was bronchitis.

Scientists say that although the complications of Covid-19 have riveted people's attention, many symptoms, such as a loss of smell, are not unique to Covid-19. Heart inflammation, lung and nerve damage and small blood clots in the lining of lungs occur in a small but noticeable percentage of patients who have had other respiratory and viral infections.

No one is saying Covid-19 is the equivalent of, say, the flu. But Covid-19 is providing a new opportunity to understand the complications of many common viral infections.

Before the pandemic, research grants to study a loss of smell were hard to come by, said Dr Danielle Reed, associate director of the Monell Chemical Senses Centre, a non-profit research group in Philadelphia.

But now, she said, "there is an explosive growth of interest among funders", adding that most who say they have lost a sense of taste have really lost a sense of smell.

Monell researchers want to compare how often people lose their sense of smell after a bout with the flu versus a bout with Covid-19 - and how long the loss lasts. Is there a genetic predisposition to this complication?

Researchers at other institutions want to know who is susceptible to heart infections, blood clots or lung damage after having a respiratory virus like the flu.

Heart problems following a viral infection are among the best studied. Every year, myocarditis - an inflammation of the heart muscle - affects as many as 1.5 million people worldwide, most of whom had a prior respiratory virus infection. Most recover fully.

But symptoms like fatigue are often not recognised as being related to myocarditis. And Dr Bruce McManus, an emeritus pathology professor at the University of British Columbia, suspects that the fatigue that sometimes follows a bout with Covid-19 might be caused by this heart problem.

"We think of Covid-19 and influenza as respiratory diseases, and in fact they are," Dr McManus said. "But the reason many patients reach their demise in many instances is myocardial."