CONTROL OF AVIAN MYCOPLASMOSES BY VACCINATION

Vaccination is an option for controlling Mycoplasma gallisepticum or M . synoviae when biosecurity measures fail to prevent the infection of poultry flocks with these mycoplasmas. Both killed vaccines (bacterins ) and living vaccines are currently in commercial use. Bacterins usual ly contain an oil emulsion adjuvant and are administered by subcutaneo us or intramuscular injection. They can reduce the decline in egg prod uction associated with M. gallisepticum, although they do not prevent infection. Newer adjuvants, such as immune stimulating complexes, may provide effective immunity without the tissue lesions caused by oil em ulsion adjuvants. Living M. gallisepticum vaccines include the F strai n and attenuated strains ts-11 and 6/85. F strain is administered in d rinking water or by aerosol. This strain reduces the decline in egg pr oduction and has been used to displace endemic strains in multiple-age flocks. The major disadvantage is the inherent virulence of F strain. Strain ts-11 is less virulent and less infectious than F strain and p rovides a somewhat weaker but usually effective, long-term protective immunity, which is vaccine-dose dependent. This strain is administered by eye drop, persists in the chicken for long periods and stimulates a detectable although variable systemic antibody response. Strain ts-1 1 can be used safely in combination with respiratory virus vaccines. S train 6/85 also stimulates a weaker protective immune response than F strain and is of low virulence and infectivity. This strain is adminis tered by aerosol, appears not to persist in vaccinated birds and may f ail to stimulate a detectable systemic antibody response. Strain MS-H is currently being evaluated as a live vaccine against M. synoviae in meat chicken breeder flocks and is often used in conjunction with stra in ts-11.