What is Psittacosis (ornithosis)?
Psittacosis, which is also referred to as ornithosis or parrot fever, is a zoonotic disease, meaning it is an illness transmitted from animals—specifically birds—to people. The condition is produced by an infection with Chlamydia psittaci, a type of intracellular bacterium. This particular organism is distinct from the chlamydial strains that are responsible for the common sexually transmitted infection in humans.
The disease characteristically manifests as an atypical pneumonia, where the infection settles in the lungs and provokes inflammation. While the lungs are the main target, the infection can sometimes spread through the bloodstream, leading to systemic effects that can involve other organs like the liver and spleen.
Causes:Psittacosis is an infection acquired directly from an avian source; it does not spread from one person to another. The illness is initiated when a specific bacterium is successfully transferred from a bird to a human through environmental exposure, following these steps:
- The Avian Reservoir: The foundational source of the infection is a bird carrying the bacterium Chlamydia psittaci. Parrots, cockatiels, parakeets, and macaws are common carriers, but pigeons and poultry can also host the organism, often without showing any outward signs of being sick.
- Release of the Bacterium: Infected birds shed the bacteria into their surroundings through their droppings (feces) and respiratory secretions. The organism is present in both wet and dry droppings and can also be found in the fine dust that is shed from their feathers.
- Environmental Aerosolization: When the bird's droppings or secretions dry out, the bacteria within them become part of fine, airborne dust particles. Activities such as cleaning a birdcage, or even the bird's own flapping and movement, can disturb this dried material and suspend it in the air.
- Inhalation by a Human Host: The infection in humans is triggered by breathing in these aerosolized, bacteria-laden particles. Once inhaled, the bacteria lodge deep within the lungs and begin to replicate, leading to the onset of pneumonia. In rarer instances, the bacteria can be transmitted through a bird's bite.
The risk of contracting psittacosis is almost entirely determined by a person's level and type of exposure to birds. While the general population has a very low risk, the following groups have a significantly increased likelihood of coming into contact with the Chlamydia psittaci bacterium.
- Owners of Pet Birds: Individuals who keep pet birds in their homes, especially species like parrots, macaws, cockatiels, and parakeets, are the most commonly affected group due to their close and frequent proximity to these potential carriers.
- Workers in Avian-Related Occupations: Anyone whose job involves routine, close contact with birds is at elevated risk. This includes veterinarians, veterinary technicians, employees of pet shops, and staff at poultry processing plants.
- Aviculturists and Bird Breeders: People who are involved in the large-scale breeding, raising, or trading of birds are at particular risk. Their work often involves managing large flocks in confined spaces, which can increase the concentration of airborne bacteria.
- Individuals with Compromised Immunity: While not a risk for exposure, having a weakened immune system puts a person at greater risk of developing a severe illness if they do become infected. Their bodies are less equipped to fight off the initial bacterial invasion.
