Chlamydophila pneumoniae in horses: a seroepidemiological survey in Italy.

We tested 731 sera from apparently healthy light horses against Chlamydophila pneumoniae, by a microimmunofluorescence (MIF) test. To verify cross-reactions with other species of chlamydiae, all sera with an antibody titre ≥32 to C. pneumoniae were tested against both C. psittaci and C. abortus. Antibodies to C. pneumoniae were detected in 194 out of 731 (26.5%) samples tested, with antibody titres ranging from 32 to 1024. No antibody titre ≥32 was detected in sera to'C. abortus. Only few sera with a high antibody titre to C. pneumoniae reacted weakly with C. psittaci at the dilution of 1:32.