A brief introduction to coronavirus disease 2019 (COVID-19) and the roles of zoonotic spillover

Coronaviruses are eminently present in animals since they were discovered over half a century ago. In 2002 and 2012 two major zoonotic emerging epidemics occurred in Asia, the Severe Acute Respiratory Syndrome (SARS) in China, and the Middle East Respiratory Syndrome (MERS), in Saudi Arabia, both extended to other countries in the regions and beyond. In 2019 the SARS-CoV-2 and the Coronavirus disease 2019 (COVID-19) begun to be apparent due to the first epidemic in Wuhan, China. All of them had a zoonotic origin, in the first two, clearer, than the current pandemic virus. In the current chapter, we discuss and explore a different point of views regarding the COVID-19 and the roles of zoonotic spillover, based on the available evidence, still on developing (March 2021).