Chlamydophila psittaci

by Olivia Saray and Joshua Lee


Chlamydophila psittaci is a species of bacteria that was first isolated from humans in Switzerland in 1879 and at this time named Pseudotyphus. The name Chlamydophila psittaci was adopted in 1890 by french scientist Morange, who isolated the same bacterium in parrots after deciphering it as a causative agent of psittacosis. C. psittaci caught the limelight in the early 1930’s when an epidemic broke out within domestic parrots and parakeets decreasing their popularity as household pets.

C. psittaci in addition to being a bacteria is also known as a zoonosis, causing infection primarily in animals but can also be contracted by humans; as a result inspection of exotic birds during importation is crucial to prevent future epidemics.


C. psittaci can be transmitted across species from bird to bird, bird to human, bird to reptiles, and bird to mammals. The bacterium is present in the tissues, feces, nasal and ocular discharge as well as plumage of infected birds. Contraction of the bacteria can occur through inhalation of particles from secretions of infected birds. It may also be transferred via physical contact of the bird’s beak with another animal or exposure due to injury, such as a bite from an infected bird. The most common method of transmission, however, is through the air.

C. psittaci presents less of a threat upon immediate release due to the fact that the organism remains viable while independent of a host. It exists as an elementary body outside of the host, meaning it can survive, but not infect, until it enters a new organism. Infected secretions eventually dry into a dusty substance, which contaminates the air. Inhalation of these particles could allow the bacterium to enter a potentially viable host and cause infection.

Once the bacterium presents itself in a new avian host, it will infect the mucosal epithelial cells of the bird and the macrophages of the respiratory tract. Macrophages, meaning “big eater”, are cells of the innate immune system that engulf pathogens. The bacterium will spread to infect other organs via the blood and result in localized infections such as pneumonitis, pericarditis, enteritis and sinusitis. If untreated the infection will eventually lead to septicemia and death of the bird.

Infection of a bird by C. psittaci will present observable symptoms in the host such as rough plumage, fever (resulting in puffiness of the bird’s feathers to keep warm), tremors, weight loss, yellow-green/greyish watery droppings, coughing and conjunctivitis.

Due to the adaptive nature of this bacterium, humans can also contract the disease and display symptoms following a 5 – 14 day incubation period. The severity of symptoms can vary from slight feelings of illness to systemic illness accompanied by severe pneumonia. More specific symptoms include fever, chills, headache, and myalgia. Humans usually contract this disease through inhalation of contaminated air or coming into direct contact with a bird, which is infected with the disease. Although the disease can be contracted through birds, transmission from human to human is rare. With modern medicine, deaths are limited to less than 1% of all reported cases, and are easily treated with antibiotics such as tetracycline.


Cases of psittacosis have been reported in at least 159 different avian species. The most common victim being parrots, but transmissions have also been widely documented from free-ranging birds including doves, pigeons, and shore birds, among others.

Though there have been several outbreaks of psittacosis, the highest rate among household parrots was in 1983 with an astonishing rate of 24% of birds admitted to veterinary clinics testing positive for the disease. This percentage was probably much higher seeing as it is likely that many cases go unreported. Psittacosis is most common among small to medium sized parrots, where 17.8% of cockatiels, 27.3% lovebirds and conures, and 17.24% of African Greys and Amazon Parrots tested positive for the disease in the 1983 outbreak.

Today, these numbers remain relatively consistent, and cockatiels remain the most prevalent species to be infected with a rate of 24.8% positive diagnosis among examined cases.

Pet shops, breeders, and farming areas are at a higher risk of experiencing an outbreak due to the large number of birds kept in close proximity to one another.

Figure 2 - Photographs depict a healthy cockatiel (left) versus one infected with Chlamydophila psittaci (right). Photos taken by Olivia Saray.

Figure 2 – Photographs depict a healthy cockatiel (left) versus one infected with Chlamydophila psittaci (right).
Photos taken by Olivia Saray.

Virulence Systems

C. psittaci is a gram negative, coccoid shaped (round), intracellular bacterium, which begins infecting a host while it is still in the elementary body phase. Only in this phase can the bacterium be freely transferred from host to host. When particles containing C. psittaci are inhaled, the bacteria will begin by attacking the host’s respiratory tract. Cells of the immune system respond to the presence of the foreign bacteria and ingest the bacteria by engulfment (known as phagocytosis) to form a phagosome. However, unlike other pathogens, upon ingestion, the bacteria do not die. Phagosomes, which are compartments formed after the bacteria is engulfed, are responsible for bringing bacteria to lysosomes, an acidic compartment in the cell. The two organelles will fuse to form a phagolysosome, which is responsible for digestion and ultimately, the death of the bacterium. In the case of C. psittaci, however, the elementary body is not killed when the phagosome and lysosome fuse; rather it is transformed into a reticulate body. A reticulate body is a bacterium that is now able to replicate. After replication of the bacterium, C. psittaci will revert back to an elementary body and exit the host cell it has infected via lysis or bursting of the cell, resulting in host cell death. The elementary body will then continue its journey and repeat the infection and proliferation process in tissues throughout the entire body of the host.


Infected birds should be kept in quarantine with proper ventilation to limit the amount of bacteria in the air. A heat lamp should be applied to maintain a cage temperature of 32℃. The environment should be kept as clean as possible. Birds should be weighed every 3-7 days to evaluate progression of the disease.

C. psittaci is highly susceptible to antibiotics such as tetracycline or its derivatives such as doxycycline or vibramycin. Tetracycline works by binding to the 30S ribosome of the bacteria, therefore inhibiting protein synthesis. This stops the proliferation of bacteria and allows the immune system to clear out the existing infection. Vibramycin is now the most commonly used antibiotic to treat psittacosis and is most effective when injected intravenously or intramuscularly (into the vein or muscle). Calcium supplements should be avoided during treatment, seeing as they bind to tetracycline and inhibit its antibacterial activity. If treatment is administered in the early stages of infection, psittacosis is rarely ever fatal.


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