Source: merckvetmanual.com
- Bacteria of the order Chlamydiales are ubiquitous, obligate intracellular gram-negative bacteria. Within the host cell, they replicate via a unique developmental cycle competing with the host for intracellular nutrient pools. Virtually any chlamydial organism can infect any eukaryotic host cell, resulting in various infections.
- Classification: A single genus, Chlamydia, is now used, as well as nine species(abortus, caviae, felis, muridarum, pecorum, pneumoniae, psittaci, suis, and trachomatis).
C abortus (formerly C psittaci serotype 1) is an agent causing primarily abortion in small ruminants, mainly sheep ovine enzootic abortion, now ovine chlamydiosis . see Enzootic Abortion of Ewes (EAE)) and goats (see Chlamydiosis (Enzootic Abortion))
Infections with C pecorum are ubiquitous in cattle herds with multiple organ manifestations (also see Abortion in Large Animals). - C psittaci is the causative agent of avian chlamydiosis (see Avian Chlamydiosis), formerly called psittacosis or ornithosis in psittacine birds or poultry/fowl, respectively
- **Transmission and Zoonotic Risks: ** Transmission of avian C psittaci strains to people may result in atypical pneumonia or even life-threatening acute illness (ie, psittacosis in people).
- Clinical findings of chlamydia infections: In general, they affect multiple organs and can generate a variety of clinical manifestations, ranging from acute to chronic inflammation and from a severe to a mild or even subclinical course. Because aerosol transmission of the pathogen is one of the main infection routes, the respiratory system is often involved.
- In birds, avian chlamydiosis is accompanied by conjunctivitis, serositis, fibrinopericarditis, hepato- or splenomegaly, anemia, and leukocytosis or monocytosis.
- Dogs infected by C psittaci (most likely transmitted from birds) present a clinical picture of bronchopneumonia that may include fever and dry cough, but also keratoconjunctivitis, GI signs (vomiting, diarrhea), and even neurologic signs. In cats, infections with C felis clinically result in rhinitis, conjunctivitis, and/or bronchopneumonia, but seropositive cats are often asymptomatic. Lambs delivered by ewes with C abortus infection may develop acute chlamydial pneumonia. They become febrile, lethargic, and dyspneic and develop a serous and later mucopurulent nasal discharge.
- In chlamydia-positive herds, newborns are free of chlamydiae but start to acquire chlamydial infections within 2 wk of birth. Thus, young animals develop more clinical signs than older ones.
- Diagnosis: Neither clinical signs nor lesions allow a definitive diagnosis of chlamydiosis. Most commercially available ELISA methods may detect infections caused by the family Chlamydiaceae but do not differentiate between chlamydial species. Sensitivity and specificity of these serologic tests are much lower than direct detection of the antigen by PCR.
- Chlmydiosis Treatment: Tretracyclines or fluoroquinolones (eg, enrofloxacin) are generally the drugs of choice. Drugs of Choice Treatment must start as early as possible and continue for at least 7 days. The classic concept of prophylactic immunization that elicits sterilizing immunity and virtually 100% protection from disease does not apply to chlamydiae. To prevent abortion in small ruminants, C abortus live vaccines are available.