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Chlamydial Pneumonia: Introduction |  |
| Chlamydiae have been identified in various parts of the world as a cause of
enzootic pneumonia in cats, calves, mice, sheep, piglets, foals, and goats. In cats, pneumonia may occur as a rare sequela of the more common chlamydial conjunctivitis and rhinitis. The main clinical sign of zoonotic chlamydiosis in humans is pneumonia, generally contracted from pet birds. |
| Etiology and Epidemiology: |
| The causative agent is
Chlamydophila (Chlamydia)
psittaci
. Some respiratory isolates from calves have properties of immunotypes 1 and 6 and are similar to strains recovered from intestinal infections (
Intestinal Chlamydial Infections: Introduction) and abortions of cattle and sheep (Abortion in Large Animals: Introduction). Immunotype 6 has been recovered from pneumonic lungs of calves and pigs. Thus, the GI tract of carrier animals should be considered as an important site in the pathogenesis of chlamydial infections and as a potential
source of the organisms. Infection most commonly occurs via inhalation of organisms from fecal carriers or other respiratory cases. Chlamydial pneumonia has affected calves under range conditions as well as on dairy farms. The disease in sheep is most frequently seen in feeder lambs assembled from different sources in feedlots or on irrigated pastures. Stressed lambs under these conditions are frequently subject to various secondary bacterial infections, which can result in
higher mortality and morbidity rates than are seen in uncomplicated chlamydial respiratory infections. |
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| Clinical Findings: |
| Calves, lambs, and goats with chlamydial pneumonia are usually febrile, lethargic, and dyspneic. They develop a serous and later mucopurulent nasal discharge with a dry hacking cough. Calves of weaning age are affected most frequently, but older cattle may also show signs. |
Lesions:
| The acute pulmonary lesion is bronchointerstitial pneumonia. The anteroventral parts of the lungs are affected but, in severe cases, entire lobes can be involved. The dry cough is attributed to tracheitis. Microscopic changes in the lungs include suppurative bronchitis and alveolitis progressing to type II pneumocyte hyperplasia and interstitial thickening due to an ingress of mixed inflammatory cells. Lymphocytic aggregates are frequently seen around airways and pulmonary
vessels. |
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| Diagnosis: |
| Neither clinical signs nor lesions allow a definitive diagnosis of chlamydial pneumonia because they are not sufficiently different from those seen in the bovine or ovine respiratory disease complex. Diagnosis requires isolation of chlamydiae from affected tissues in tissue culture or chick embryo. Chlamydial inclusion bodies may be detected in affected tissues. Diagnosis may be supported by fluorescent antibody tests and serologic assays performed on acute and convalescent
samples. Predominantly, IgG2 antibodies are induced by chlamydial infections in cattle. Subclinical chlamydial infections occur as well. |
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| Prevention and Treatment: |
| Vaccines are not available. Several antimicrobials (eg, penicillin, erythromycin, tylosin, and tetracyclines) can interfere with chlamydial replication, but tetracycline is generally the drug of choice. Treatment must start as early as possible and continue for at least 5-7 days. |
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