Coronaviruses primarily infect the upper respiratory and gastrointestinal tract of mammals and birds. Six different currently known strains of coronaviruses infect Human s. The most recently publicized Human coronavirus, SARS-CoV which causes SARS, has a unique pathogenesis because it causes both upper and lower respiratory tract infections and can also cause gastroenteritis. Coronaviruses are believed to cause a significant percentage of all common colds in Human adults. Coronaviruses cause colds in Human s primarily in the winter and early spring seasons.