Immunity to mycoplasma infections of the respiratory system in the domestic fowl and turkey.

The mycoplasma infecting and sometimes causing disease of the respiratory system in both species are M. gallisepticum and M. synoviae, while M. meleagridis affects the turkey only. M. gallisepticum has received the greatest attention and natural infection is reported to result in protection varying greatly in degree and duration. Vaccination with living organisms either by the respiratory or intravenous routes results in a high degree of protection against air sac challenge for at least a few weeks. Killed organisms administered intravenously result in a lesser degree of protection to this challenge but when given intranasally provide no protection. M. gallisepticum survives in the respiratory tract and perhaps in other organs and tissues for long periods after infection, perhaps in latent form. However, intercurrent infection and other avian respiratory pathogens may precipitate multiplication of the organism and disease in birds apparently resistant to challenge with mycoplasma alone. The mechanism of protection has not been extensively studied and production and significance of local antibody or a cell-mediated response have not been determined. However, bursectomized chickens vaccinated against M. gallisepticum show much less resistance compared with controls but the exact part played by humoral antibody is still in doubt. Similar observations have been made with M. synoviae.