Psittacosis: causes and pathogenesis
Last reviewed: 23.04.2024
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The causative agent of ornithosis is Chlamydophila psittaci, the genus Chlamidia of the Chlamidiaceae family , an obligate intracellular parasite. Propagated by binary fission in the cytoplasm of affected cells. Chlamydia can form L-forms. They have thermolabile antigens. Pathogenicity factors are surface exotoxins and LPS (endotoxin). Cultivated in tissue cultures and in chick embryos. Highly resistant to the environment. Sensitive to the means of disinfection.
Epidemiology of ornithosis
The reservoir and source of the pathogen are various kinds of wild synanthropic ones. Ornamental and domestic birds, in which ornithosis occurs in the form of carriers; or acute intestinal infection. The mechanism of transmission of the causative agent is aerosol. The transmission path is air-dust. A fecal-oral mechanism is possible: by the food route of transmission of infection (up to 10% of cases). Ornithosis - a widespread disease, is recorded in the form of sporadic cases and group production or family outbreaks. It is established that 10-20% of community-acquired pneumonia have ornithic etiology. The greatest epidemiological significance are birds of the parrot and pigeon family. Infestation of urban pigeons fluctuates between 30-80%. Significant infection is noted among crows. Ornithosis in birds is manifested by rhinitis, diarrhea, adynamia, refusal to eat, sticking of feathers. Sick birds, especially decorative birds, often die. Infected birds excrete the pathogen with feces and nasal secretions. Possible transovarial transmission of the pathogen in two or more generations. The infection of a person is due to contact with birds, infected care items and poultry products.
The susceptibility of man to ornithosis is high. Mostly people of middle age and older are sick, children rarely. Immunity is unstable, there are cases of recurrent disease. In a number of cases, long-term carriers are formed in the patients. Both carriers and patients with ornithosis people, as a rule, do not pose a danger to others. However, single reliable cases of infection of nurses serving patients with ornithosis are described.
Pathogenesis of ornithosis
The causative agent penetrates the mucous membranes of the upper respiratory tract and is fixed in the epithelium of the bronchi, bronchioles and alveoli, where its reproduction takes place, which causes cell death, release of the pathogen and its toxins. Bacteriemia and toxemia develop and, as a consequence, fever and intoxication. Significant importance is attached to the secondary bacterial flora. S. Psittaci can affect the lungs, bronchi, liver, spleen, heart muscle. CNS. By suppressing protective mechanisms, the causative agent is able to persist for a long time in macrophages, reticuloendothelial cells and respiratory tract epithelia, which explains the possibility of prolonged, recurrent and chronic course of the disease. With oral infection, the causative agent does not cause any changes in the organs of the digestive tract, and there are no symptoms of the respiratory tract, i.e. A typhoid-like (febrile) form of the disease develops.
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