Boring Things I Coronaviruses are a group of viruses covered in little protein spikes that look like a crown. There are hundreds of known coronaviruses. Seven of them infect humans, and can cause disease. The coronavirus SARS-CoV causes SARS, MERS-CoV causes MERS, and SARS-CoV-2 causes the disease COVID-19. Of the seven human coronaviruses, four cause colds, mild, highly contagious infections of the nose and throat. Two infect the lungs, and cause much more severe illnesses. The seventh, which causes COVID-19, has features of each: it spreads easily, but can severely impact the lungs. Coronaviruses transmit best in enclosed spaces, where people are close together. Cold weather keeps their delicate casing from drying out, enabling the virus to survive for longer between hosts, while UV exposure from sunlight may damage it. But because no one (except me and approximately 6 million people) is yet immune to a new virus, it has so many potential hosts that it doesn’t need ideal conditions to spread. In the body, the protein spikes embed in the host’s cells and fuse with them enabling the virus to hijack the host cell’s machinery to replicate its own genes. Coronaviruses store their genes in RNA. All viruses are either RNA viruses or DNA viruses. RNA viruses tend to be smaller, with fewer genes, meaning they infect many hosts and replicate quickly in those hosts. In general, RNA viruses don’t have a proofreading mechanism, whereas DNA viruses do. So when an RNA virus replicates, it’s much more likely to have mistakes called mutations. Many of these mutations are useless or even harmful. But some make the virus better suited for certain environments - like a new host species.