The virus affects the human system during winter and early spring. This virus is behind 20% of colds. There are more than 30 types of coronavirus, out of which only 3 or 4 ones are harmful. There are many varieties of coronavirus that affect animals, and up to six can affect humans. This type of virus typically causes mild to moderate upper SARS (severe acute respiratory syndrome). Coronaviruses cause acute, mild upper respiratory infection (common cold). Coronaviruses are found in avian and mammalian species. They resemble each other in morphology and chemical structure: for example, the coronaviruses of humans and cattle are antigenically related. There is no evidence, however, that human coronaviruses can be transmitted by animals. In animals, various coronaviruses invade many different tissues and cause a variety of diseases, but in humans they are only proved to cause mild upper respiratory infections, i.e. common colds. On rare occasions, gastro...