Coronaviruses are a family of viruses, some of which cause respiratory illness in humans. Coronaviruses have been found circulating among animals, such as camels, cats and bats and a few have jumped to people - a spread that is defined by epidemiologists as "zoonotic." Prior to December 2019, there were six coronaviruses that were known to have circulated among people. Four cause about 25% of colds. Onecaused Severe Acute Respiratory Syndrome (SARS), a disease that emerged in China in 2002, and another that causes Middle East Respiratory Syndrome (MERS). In December, another coronavirus emerged that shared some of the same genes as SARS, and therefore has been named SARS-CoV-2019 by the World Health Organization. The understanding of this virus, which causes the disease COVID-19, is evolving almost daily, as scientists have raced to understand how contagious it is, its incubation period, it's morbidity and mortality rate, and how it passes between people.