Historical Background and Terminology
The first detailed clinical description of the disease was made by researcher F. Jürgensen in 1876. He observed an outbreak of severe pneumonia directly linked to patients' contact with parrots. Because of this etiological connection, the disease received its historical name — psittacosis (from the Greek word psittakos, meaning "parrot").
Half a century later, in 1930, scientist S. Bedson successfully isolated a specific microorganism directly from sick humans. Subsequent research reliably established that the natural reservoir of infection includes not only exotic parrots but also many other bird species. To reflect this fact, medical terminology was expanded to include the more universal term — ornithosis (from the Greek root ornis — bird).
Epidemiology
In terms of its epidemiological status, ornithosis is classified as a zoonosis. The natural reservoir and sources of the pathogen in nature include over 170 species of wild, synanthropic, and domestic birds. Transmission most frequently occurs from pigeons, ducks, canaries, and sparrows. Strains isolated from parrots and fatal human cases exhibit maximum virulence. Occasionally, sources may include bird ectoparasites, rats, and other small animals.
Transmission from an infected human to a healthy person is extremely rare in clinical practice.
Main routes and mechanisms of transmission:
- Aerogenic mechanism (primary). Realized via airborne and dust-borne pathways when inhaling particles containing the pathogen.
- Contact route. Accidental transfer of the microorganism by unwashed hands to vulnerable mucous membranes of the eyes or nose is possible.
- Fecal-oral mechanism (rare). Alimentary infection occurs when consuming meat from an infected bird that has not undergone sufficient thermal processing.
Human susceptibility to the pathogen is very high. The disease typically manifests as sporadic cases, though occupational outbreaks in risk groups (poultry farm workers, meat-processing plant workers, and livestock farm employees) are characteristic.
Pathogenesis and Organ Damage
The development of the infectious process in ornithosis follows a strict sequence:
- Portals of entry: The infection invades through the mucous membranes of the respiratory tract.
- Adhesion and invasion: Due to high epitheliotropism, the pathogen penetrates epithelial cells of the bronchi, small bronchioles, and alveoli.
- Replication: Intracellular replication is triggered, leading to host cell death and destruction followed by a local inflammatory response.
- Toxemia: A massive release of toxins and cellular breakdown products causes a severe systemic toxic syndrome.
- Generalization (bacteremia): Chlamydiae break into the bloodstream and disseminate throughout the body.
- Organ lesions: Secondary foci form in parenchymatous organs (causing hepatolienal syndrome — enlargement of the liver and spleen), alongside involvement of the central nervous system, heart, blood vessels, and joints.
- Immunopathology: Systemic allergic sensitization of the body develops against the backdrop of the infection.
Clinical Presentation of the Initial Period
The latent incubation period for ornithosis is relatively short, ranging from 6 to 10 days. The disease begins with acute clinical manifestations.
The patient experiences a rapid and sharp rise in body temperature to high levels (38–40 °C). Fever is always accompanied by pronounced symptoms of general intoxication. A key clinical manifestation of the initial period is the development of severe pneumonia, which frequently proceeds with a dangerous hemorrhagic component. Concurrently, central nervous system involvement begins to unfold, accompanied by hepatomegaly and splenomegaly.