Introduction

Classification

Taxonomy

• Order: Chlamydiales.
• Family: Chlamydiaceae.
• Genus: Chlamydia.

Etymology

• Gk: chlamys - a cloak.

Active Forms

Clinical Effects

Epidemiology

Transmission

• Inhalation or ingestion of infectious material, eg respiratory discharges and feces.
• Vertical transmission via the egg occurs in some birds.

Pathological effects

• Presenting condition and severity of disease related to immunological state of the host animal.
• Often partial immune response → chronic relapsing infection.

• Pathogenicity related to age, sex and health of host animal; route of infection; infective dose; strain and virulence of organism.
• In birds: causes pneumonia, pericarditis, diarrhea, encephalitis, conjunctivitis.
• In mammals: causes enzootic abortion of ewes, abortion of cows, genital infections, mastitis, intestinal infection and diarrhea, pneumonia, arthritis, encephalitis, conjunctivitis, hepatitis.
• In humans: causes pneumonia, psittacosis/ornithosis, abortion, conjunctivitis.
• Cats: respiratory disease; mainly persistent conjunctivitis.

Other Host Effects

• The gastrointestinal tract is the natural habitat in both mammals and birds.
• Inapparent infections may occur with prolonged fecal shedding.
• Psittacosis (infection due to C. psittaci in psittacine birds) and ornithosis (infection due to C. psittaci in non-psittacine birds) may result in a carrier state after recovery, and stress may cause recurrence.

Control

Control via chemotherapies

• Tetracycline Tetracycline.

Control via environment

• Zoonotic risk; pregnant women should avoid contact with lambing sheep.

Vaccination

• Killed and live attenuated vaccines available for cats.
• Live attenuated vaccines for sheep.

Diagnosis

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.