The major symptoms of COVID-19, according to public health authorities, are a cough, fever and difficulty breathing.

But other symptoms have since joined the list.

Reports of COVID-19 patients who have lost their sense of taste and smell, who are showing signs of unusual blood clots, lesions on their feet that are sometimes called “COVID toes”, headaches, nausea, and rare inflammatory diseases in pediatric patients have all hit the news over the last few weeks. It seems like the list of possible symptoms of COVID-19 just keeps getting longer.

So how does a single virus cause so many symptoms?

One possible explanation: it doesn’t.

Dr. Gerald Evans, chair of the division of infectious diseases at Queen’s University, suggests that many of the symptoms currently being ascribed to COVID-19 are already present at similar levels in the general population, or are the effects of any severe infection — not just infections from the novel coronavirus.

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For example, he said, conjunctivitis is present in about 0.8 per cent of COVID-19 cases according to one study.