Mycoplasma gallisepticum(MG) is a common respiratory disease in commercial layers around the world. Mycoplasma are a small primitive type of bacteria and various species of Mycoplasma are host-adapted to different animal species. Chickens can also be infected with the generally less pathogenic Mycoplasma synoviae (MS) and several other Mycoplasma species that are considered non-pathogenic. Besides infecting chickens, MG causes serious respiratory disease in turkeys and has been found in a number of other avian species. In parts of the U.S., a common wild bird, the house finch, has been found to be infected with MG.