In 400 BC, the renowned Greek physician Hippocrates offered the earliest known account of a seasonal respiratory disease. The “Cough of Perinthus” was a winter affliction that hit a port city in Greece. Symptoms included fevers, chills, labored breathing, pneumonia, and sometimes death.
In 1856, the Scottish geographer Alexander Keith-Johnston depicted how some prominent viruses and other diseases were thought to vary in relation to temperature and latitude (see the map below). Modern scientific tools have allowed us to observe and explain disease in ways that may have astounded Hippocrates and Keith-Johnston. But explaining why some disease outbreaks have seasonal cycles, and predicting the timing of those cycles, remains a challenging problem.
In 2020, solving that problem became even more pressing, as a novel coronavirus (SARS-CoV-2) and the respiratory disease it causes (COVID-19) spread rapidly around the world.
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Image via NASA Earth Observatory