The coronavirus SARS-CoV causes the disease called SARS, MERs –CoV causes the disease MERS. And SARS-CoV2 causes the diseases COVID -19. Of the seven coronaviruses, four of them cause colds, and mild, highly contagious infections of the nose and throat. Two of the virus infect the lungs and causes much more severe illness. The seventh, which causes Covid-19 has features of each: it spreads easily and can severely impact the lungs.