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Ornithosis - Causes and Pathogenesis
Last reviewed: 04.07.2025
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The causative agent of ornithosis is Chlamydophila psittaci, genus Chlamidia, family Chlamidiaceae, obligate intracellular parasite. It reproduces by binary fission in the cytoplasm of affected cells. Chlamydiae are capable of forming L-forms. They have heat-labile antigens. Pathogenicity factors are surface exotoxins and LPS (endotoxin). They are cultivated in tissue cultures and on chicken embryos. They are highly resistant in the environment. Sensitive to disinfectants.
Epidemiology of psittacosis
The reservoir and source of the pathogen are various species of wild synanthropic, ornamental and domestic birds, in which ornithosis occurs as a carrier; or acute intestinal infection. The mechanism of transmission of the pathogen is aerosol. The route of transmission is airborne dust. The fecal-oral mechanism is possible: by food transmission of infection (up to 10% of cases). Ornithosis is a widespread disease, recorded in the form of sporadic cases and group industrial or family outbreaks. It has been established that 10-20% of community-acquired pneumonia have ornithosis etiology. Birds of the parrot and pigeon families are of the greatest epidemiological significance. The infection rate of urban pigeons ranges from 30-80%. Significant infection is noted among crows. Ornithosis in birds is manifested by rhinitis, diarrhea, adynamia, refusal to eat, and feather sticking together. Sick birds, especially decorative ones, often die. Infected birds excrete the pathogen with feces and nasal secretions. Transovarial transmission of the pathogen in two or more generations is possible. Humans become infected through contact with birds, infected care items, and poultry products.
Human susceptibility to ornithosis is high. People of middle and old age are mostly affected, children - rarely. Immunity is unstable, cases of repeated illness are known. In some cases, those who have had the disease develop a long-term carrier state. Both carriers and people with ornithosis, as a rule, do not pose a danger to others. However, isolated reliable cases of infection of nurses serving patients with ornithosis have been described.
Pathogenesis of ornithosis
The pathogen penetrates through the mucous membranes of the upper respiratory tract and is fixed in the epithelium of the bronchi, bronchioles and alveoli, where it reproduces, causing cell death, the release of the pathogen and its toxins. Bacteremia and toxinemia develop and, as a consequence, fever and intoxication. The addition of secondary bacterial flora is of great importance. C. psittaci can affect the lungs, bronchi, liver, spleen, heart muscle. CNS. By suppressing defense mechanisms, the pathogen is able to persist for a long time in macrophages, reticuloendothelial cells and the epithelium of the respiratory tract, which explains the possibility of a protracted, recurrent and chronic course of the disease. With oral infection, the pathogen does not cause any changes in the organs of the digestive tract, there are no symptoms of damage to the respiratory tract, i.e. a typhoid-like (febrile) form of the disease develops.
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