A family not to be associated with

The bacterium Chlamydia psittaci is part of the chlamydia1 family. All the bacteria from this family are strictly intracellular2. Two other members of this family are quite famous; Chlamydia pneumoniae, which causes pneumonia and especially Chlamydia trachomatis, which causes a sexually transmitted infection or, in some countries, an infection of the cornea called trachoma3.


Due to the birds

This bacterium is transmitted to humans by birds, especially parakeets and parrots, but also by pigeons, sparrows, and reared poultry, such as turkey or ducks.

Infected birds do not show any symptoms during several months. Yet they excrete the bacteria in their droppings or through their nasal secretions and humans can get infected through inhaling it.


In 1879, seven members of a family near Z├╝rich (Switzerland) suddenly fell ill with severe pneumonia. In fact, this rich family had just bought a parrot from overseas. A Swiss doctor established a link between the bird and the human disease. At the time, he was not able to figure out, which bacteria were responsible for the disease. It was only in 1929 that Chlamydia psittaci was identified during a poultry livestock outbreak, which caused the death of 300 people in Europe.



This bacterium can also be transmitted when an infected bird bites, via contacts from mouth to beak, or when manipulating their feathers. There is no transmission from human to human, meaning that an infected person cannot transmit the bacteria to anyone directly

A disease of varying severity

The disease caused by Chlamydia psittaci is called psittacosis. It usually is a simple infection with some fever and symptoms resembling the flu. Sometimes it can evolve towards severe pneumonia, which can be fatal if not treated. Thankfully, antibiotics4 can easily cure this type of infection. Psittacosis is rare, as most birds are not infected and if it occurs, it is often diagnosed as a flu.



Chlamydia1 = There are several species of Chlamydia. They can cause a broad range of diseases. One of these bacteria, Chlamydia trachomatis is responsible for a rather frequent sexually transmitted infection (STI), touching about 5% of the sexually active population in Europe. The infection is often asymptomatic and usually goes unnoticed. Women, who have been exposed to Chlamydia trachomatis can become sterile or suffer a miscarriage.

Intracellular2 = Defines a bacterium that needs to be inside a cell to survive and multiply. Some bacteria are strictly intracellular, since they cannot multiply outside of a cell. Then there are facultative intracellular bacteria that can replicate even without a host cell. The strictly intracellular bacteria are difficult to grow in the laboratory and thus often remain undetected with cultivation methods routinely used for diagnostic purposes.

Trachoma3 = Eye infection, which initially affects the eyelid but over time can cause lesions of the cornea leading to blindness. Trachoma is particularly present in sub-Saharan Africa and can be transmitted through flies. It is the main cause of blindness of infectious origin.

Antibiotic4 = A drug which allows to kill bacteria or at least to stop their growth. Antibiotics act against bacteria, but do not help treat diseases caused by viruses and parasites.