Poor serologic response to upper respiratory infection with Mycoplasma synoviae in turkeys

Mycoplasma synoviae (MS) was isolated from a flock of commercial tom turkey s in which a small percentage of the birds exhibited clinical signs and les ions typical of MS synovitis. However, serologic testing of such flocks rev ealed poor to inconsistent reactivity by agglutination, enzyme-linked immun osorbent assay (ELISA) or hemagglutination inhibition; isolation of MS from such flocks proved to be very difficult. Turkeys were challenged with one of the isolates (K4463B) either by aerosol or systemically by a combination of intravenous, foot pad, and eyedrop routes. Turkeys challenged by the sy stemic route responded normally to all serologic tests, whereas those chall enged by aerosol either responded very poorly on all serologic tests or wer e seronegative up to 6 wk postchallenge even though they were positive for MS by tracheal culture. These results suggest that turkeys may harbor an up per respiratory infection with MS while remaining serologically negative.