Chlamydia Abortus

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Chlamydia abortus

Also known as

Psittacosis, Chlamydophila abortus, Chlamydiosis, Enzootic Abortion


Chlamydia abortus is a species of Chlamydiae (gram negative bacteria) that causes abortion and fetal death in mammals, including humans. C. abortus (formerly C.psittaci serotype 1) can cause abortion in small ruminants, mainly sheep and goats, but also in cattle.

Abortion in cattle can be caused by Chlamydia abortus, Chlamydia psittaci and Chlamydia pecorum. C. psittaci is the causative agent of psittacosis or ornithosis disease in humans and birds. It also causes acute pneumonia in cattle and sheep. Chlamydia pecorum is a common but under-recognized cause of disease in livestock.

Abortion due to Chlamydia in cattle occurs during the sixth to eighth month of gestation, particularly among heifers in their first pregnancy. Some cows give birth to infected, weak, premature calves.

Chlamydia abortus strains have been found worldwide in cases of abortion, most commonly in sheep flocks that are closely confined.

Usually, livestock become affected after introduction of normal-appearing carrier animals into the herd. Chlamydial infection in sheep most likely occurs at lambing time by ingestion of the pathogen excreted by infected and aborting ewes in diseased placentas, uterine discharges, and feces. In sheep, the infection generally remains at a subclinical level until the last 4 weeks of the next pregnancy.

Infection of cattle with any type of chlamydiae is ubiquitous, with mixed infections occurring frequently. The lack of association between infection and clinical disease has resulted in debate as to the pathogenic significance of these organisms, and their tendency to sub-clinical and/or persistent infection makes it challenging to the study their effects.

Recent evidence, however, indicates that chlamydial infections have a substantial negative impact on livestock productivity due to chronic, recurrent infections associated with pulmonary disease in calves and infertility and sub-clinical mastitis in dairy cows.

Most chlamydial infections in livestock do not result in clinical illness, but may lead to chronic or recurrent chlamydial infections on a subclinical level. Because of the role of chlamydia as co-pathogens, or latent persisting infections that affect animals in subtle ways, chlamydial infections are probably economically more important than rare outbreaks of severe chlamydial disease.

Joint and central nervous system infections are also seen. Mixed infections are common in herds and even in individual animals. Research also suggest that these infections tend to show up when they coincide with other risk factors such as stress and other diseases.

In acute infection, clinical signs include fever and depression. The respiratory form may affect upper airways as well as the lower respiratory tract and result in pneumonia with typical signs (nasal secretions, cough, and difficult breathing).

In cows, chlamydial infections can be associated with abortion, infertility, and mastitis. Other manifestations of acute chlamydiosis include enteritis (intestinal infection) and diarrhea, polyarthritis (infection in multiple joints), keratoconjunctivitis (inflammation of the cornea and conjunctiva), encephalomyelitis (inflammation of the brain and spinal cord), pericarditis (inflammation of the sac around the heart), or hepatitis (inflammation of the liver.

In chlamydia-positive herds, newborns are free of chlamydiae but start to acquire chlamydial infections within 2 weeks of birth. Young animals develop more clinical signs than older ones.


  • Fever
  • Depression
  • Nasal secretions
  • Cough
  • Difficult breathing
  • Abortion
  • Diarrhea
  • Lameness


Most types of Chlamydia are transmissible among species, including people. C. abortus may cause abortion and fetal death in pregnant women after transmission from goats or sheep. Chlamydial abortion in cattle and other species is similar to abortion patterns in sheep, but much more sporadic and less common.

Transmission of the disease in cattle occurs similarly to that in sheep, mostly by ingestion of infected tissues during calving season, but C. abortus also causes seminal vesiculitis in bulls and rams, and may be transmitted in semen (as well as causing poor semen quality).

Chlamydial infections affect multiple organs and can create a variety of clinical signs, ranging from acute to chronic inflammation and from severe to mild or even subclinical disease. Aerosol transmission of the pathogen is one of the main infection routes; thus the respiratory system is often involved.

In cattle and pigs, chlamydial infections are widespread but often underdiagnosed. These pathogens have been isolated from a group of calves with pneumonia, systemic disease, and intestinal infections. Cultures of nasal and rectal samples from clinically normal young calves revealed a large percentage of subclinical infections during at least the first 30 days of age.

Long-lasting latent (hidden) infections have been documented in many species, including cattle. In some studies, Chlamydia have been found in the feces of 60% of normal calves. Clinical disease may not appear unless immune defenses are compromised by stress, other infections, nutritional deficiencies, or other factors.

Diagnosis is often difficult due to lack of characteristic clinical signs, or concurrent infection with other intestinal and respiratory pathogens, and the presence of Chlamydia in clinically normal calves. This organism is not easy to culture in the laboratory, and most diagnostic laboratories do not check for it.

Neither clinical signs nor lesions provide a definitive diagnosis. Detection of Chlamydia is not part of routine veterinary bacteriologic diagnosis; infections caused by these intracellular pathogens have been underestimated because isolation of the pathogen depends on specialized cell culture techniques.


There have been a number of attempts in the past 70-plus years to create an effective vaccine to protect livestock from Chlamydia infections but none have been very successful. Currently, only two chlamydial vaccines are available commercially and they target C. felis in cats and C. abortus in sheep, but not cattle.


Several antimicrobial products (tetracyclines, quinolones, macrolides, lincosamides, rifamycins) can hinder chlamydial replication. Tretracyclines or fluoroquinolones (enrofloxacin) are generally the drugs prescribed. To be effective, however, treatment must start as early as possible and continue for at least 7 days.

No antibiotic treatment for chlamydiae is truly bactericidal, however. It is suspected that antibiotics frequently induce persistent chlamydial infections by reducing host immunity--by suppressing antigen production while not completely eliminating the pathogen.

About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.