Psittacosis

The causative agent of parrot fever (= psittacosis) is the gram-negative bacterium Chlamydia psittaci. The bacterium belongs to the group of chlamydia and is the causative agent of ornithosis in birds and humans.

Occurrence

The pathogen occurs worldwide. The disease is notifiable as soon as psittacosis is detected in parrots and parakeets (Psittaciformes). If birds of other species are infected with chlamydia, this infection is called ornithosis. Psittacosis is a zoonosis (i.e. a disease that can be transmitted from animals to humans), but is generally rare.

Host animals

The natural reservoir of C. psittaci are all birds (parrots, pigeons, gulls, ducks, turkeys, chicken, ...). Other chlamydia also occurs in mammals (cats, dogs, goats, sheep, cows, pigs...).

Mode of transmission

All secretions and excretions are infectious. The pathogen is usually ingested with droplet infection by inhaling infectious faeces and dust or aerosols.

Incubation period

3 to 29 days

Symptoms

Symptoms in birds are pneumonia, coughing, emaciation, ruffled feathers, diarrhoea, eye and nose discharge. Death may occur after a few days to several weeks or the disease may become chronic, in which the birds appear to recover but continue to shed pathogens.

Therapy

The means of choice for therapy are tetracyclines (oxytetracyclines), which must be given on a long-term basis.

Prevention

As a preventive measure, birds must be placed in quarantine and tested for chlamydia after purchase. The usual hygiene measures for handling animals must be followed. Be careful when in direct contact with bird excrements. It is recommended to wear protective mask, gloves and protective clothing when handling infected birds. Psittacosis is a notifiable animal disease according to the Animal Diseases Act. Direct vaccination against the pathogen is not possible.

In 2019, 67 molecular biological examinations of various birds (pigeons, parakeets, parrots, canaries, other ornamental birds, etc.) were done - 16 of them were positive for C. psittaci, 13 of which came from a single aviary.

In Austria, psittacosis has to be reported according to § 16 of the Animal Diseases Act. Suspicion of psittacosis must be reported to the official veterinarian. If the clinical symptoms and the diagnostic evidence of C. psittaci are present, the official veterinarian will decide whether a ban/treatment is necessary - depending on the course of the disease.

Synonyms: Avian Chlamydiosis, Psittacose, Parrot fever, Ornithosis

Chlamydia psittaci is an obligatory intracellular pathogen and occurs in different forms: as elementary body (infectious form), as intermediate body, and as initial body. The individual species of chlamydia show a high degree of host adaptation: C. psittaci occurs mainly in psittacids, small ruminants and humans, C. abortus in sheep and goats, C. trachomatis in humans (eye infection).

Differential diagnoses include infections such as avian influenza, mycoplasma pneumonia, Q fever, brucellosis and tularemia.

Mode of transmission

All secretions and excretions are infectious. The pathogen is usually taken up by droplet infection from inhalation of infectious faeces, dust or aerosols. With this mode of transmission, the upper respiratory tract is the most likely entry point. Transmission may also occur by contact or smear infection. Humans in close contact with infectious animals are the ones most likely to become infected. In humans, the disease is usually transmitted aerogenously by inhaling infectious faeces and dust. The incubation period is 3-29 days, but can also be up to 100 days.

Symptoms

Symptoms in birds are pneumonia, coughing, emaciation, ruffled feathers, diarrhoea, eye and nose discharge. The disease leads to death within a few days to weeks. The disease can also become chronic, animals seem to recover but they are still shedding pathogens. In humans, general symptoms with fever and subsequent pneumonia usually occur.

Suitable sample materials are

• Organs
• faeces, faecal swabs
• Cloacal swabs

Laboratory diagnosis is performed by direct detection of chlamydia DNA. In positive cases Chlamydia psittaci differentiation from other species is performed by molecular biological methods (PCR). Spleen and liver swelling are particularly important indicators of psittacosis. During the dissection of birds, these changes must be taken into account for differential diagnosis. Cultivation of C. psittaci is difficult and can be done only by a few special laboratories. A diagnosis by detecting specific antibodies in serum of birds cannot be done, this is only possible in ruminants, pigs, horses or small animals.