Chlamydophila abortus is a species in Chlamydiae that causes abortion and fetal death in mammals, including humans. Chlamydophila abortus was previously classified as Chlamydia psittaci along with all Chlamydiae except Chlamydia trachomatis. This was based on a lack of evident glycogen production and on resistance to the antibiotic sulfadiazine. In 1999 C. psittaci and C. abortus were recognized as distinct species based on differences of pathogenicity and DNA-DNA hybridization. C. abortus has not been isolated from birds.