Chlamydia psittaci infection of horses with respiratory disease.

Two strains of Chlamydia psittaci were isolated from the nasal tract of horses with acute respiratory disease. These 2 isolates (NS 121 and NS 172) were characterized as chlamydia on the basis of their morphology, tinctorial property, growth in chicken embryos, inability to grow on bacterial media and their possession of chlamydial common complement fixing group antigen. They were identified as C. psittaci on the basis of resistance to sodium sulphadiazine. The present strains were not pathogenic to mice and guinea pigs and non-toxigenic. They induced antibodies and caused latent infection in mice and guinea pigs. Acute and convalescent sera were avaliable from one of the horses and rising levels of specific antibody were demonstrated. No chlamydia were isolated from the materials of 14 aborted foals, 4 synovial fluids from horses with acute polyarthritis and nasal, tracheal and lung material from another 276 horses.