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Synonyms: Chlamydophila psittaci infection, Chlamydia psittaci infection, ornithosis, parrot fever, chlamydiosis
This zoonosis is caused by infection with the obligate intracellular bacterium Chlamydophila psittaci, formerly known as Chlamydia psittaci. The bacterium infects psittacine birds – parrots, parakeets, cockatoos and lories. A large number (>100) of avian species such as canaries, budgies, pigeons and other birds that are commonly kept as pets are also susceptible to the disease. It can also affect domesticated fowl such as turkeys and ducks. The term ornithosis is used to denote infection transmitted from a non-psittacine source. An epidemic outbreak of the infection occurred in birds and humans in 1929-1930, affecting thousands of birds and hundreds of people, which led to the initial isolation and characterisation of the bacterium. Outbreaks of the disease are now rarer due to stricter import controls on birds, better veterinary and medical knowledge and increased awareness among bird owners.
It may affect domestic bird owners and is an occupational disease of zoo and pet shop workers, poultry farmers and vets. Some strains of the species may affect sheep, goats or cattle, causing chronic infection/abortion and, rarely, can affect humans working with these animals. Human-to-human transmission is a rare event but is thought to be associated with a more severe form of the disease; however, some experts dispute that this occurs.
- Birds infected with the organism may be apparently healthy but are often ill or succumb. Thus a history of recent contact with an ill or dead bird preceding illness in a human indicates the need to consider this diagnosis.
- Infection occurs through inhalation of aerosolised bacteria from avian faeces, feather dust or respiratory secretions. Cases have been reported following oral contact with birds (eg giving resuscitation) and from handling plumage or infected tissues.
- The organism is resistant to drying and can survive for several months in bird dander or faeces.
- The inoculum enters the bloodstream via the lungs and enters the reticuloendothelial system, with secondary bacteraemia leading to respiratory infection.
- It is a rare illness. Figures from the Health Protection Agency (HPA) indicate that there were about 500 reported cases in the UK in the mid 1990s, decreasing to about 100 annually in recent years. There were 59 cases in 2005.
- It is thought there is a significant amount of underdiagnosis and under-reporting based on population sero-surveillance studies. The HPA requests that they be informed of any cases, particularly those connected with pet retailers.
Working with birds, pet bird ownership, pigeon fancying, and contact with ill birds.
- Classically, it presents as a community-acquired pneumonia with flu-like symptoms. There are marked signs of systemic illness/constitutional upset. There is often fever and chills with lassitude. It may develop mildly and insidiously or develop into overwhelming sepsis with acute respiratory failure.
- Respiratory symptoms include a nonproductive cough, dyspnoea, sore throat, nose bleeds and, rarely, pleuritic chest pain.
- Gastrointestinal symptoms occur less often. Rarely, the disease causes nausea and vomiting, abdominal pain, diarrhoea and jaundice.
- Neurological symptoms are common - particularly severe headache and also photophobia. It may cause agitation or extreme malaise and lassitude.
- Dermatological manifestations include a facial macular rash known as Horder spots (appearance similar to rose spots of typhoid fever).
- There may be signs of pneumonic consolidation, but often the chest examination is rather nonspecific and not concordant with the severity of pulmonary involvement revealed by CXR.
- Relative bradycardia may be present (ie slow heart rate given severity of fever). There may be signs of pericarditis, endocarditis or myocarditis.
- Splenomegaly is relatively common, affecting about two-thirds of sufferers, and should prompt consideration of this diagnosis if found in conjunction with pneumonia.
- As well as Horder spots there may be erythema nodosum or erythema multiforme.
- A polyarticular reactive arthritis may be seen.
- Rarely, there may be features of meningitis, encephalitis, seizures or Guillain-Barré syndrome.
- Extrinsic allergic alveolitis (bird fancier's lung)
- Pneumonia due to atypical pathogens, eg Legionella spp. and Mycoplasma spp.
- Q fever
- Infective endocarditis
- Bacterial pneumonia
- Viral pneumonia
- Typhoid fever
- Avian influenza
- FBC may show normal or mildly neutropenic white cell count. ESR may be raised.
- U&E should be normal unless there are renal complications.
- LFTs tend to show mild-to-moderate derangement.
- Urinalysis may show proteinuria.
- CXR tends to show widespread dense streaky opacities predominantly affecting the lower lobes but there are no radiological features that allow differentiation from other causes of pneumonia.
- Culture of C. psittaci is usually avoided due to its hazardous nature.
- Diagnosis is usually confirmed by the presence of a fourfold rise in antibody titre between acute and convalescent sera. These paired sera (blood samples collected two weeks apart) are tested for chlamydial antibodies.
- Polymerase chain reaction (PCR) and microimmunofluorescence techniques are being developed but currently remain experimental.
- Enzyme-linked immunosorbent assay (ELISA) testing has been used to confirm the diagnosis.
- Infection in birds can be detected using PCR-based testing kits.
- Tetracycline or doxycycline are the usual first-line antibiotics of choice. Treatment is normally given for 2-3 weeks to lower the risk of relapse. Patients normally show a response within 24-72 hours.
- Erythromycin is a good second-line agent and often used in young children or pregnant women where tetracyclines are contra-indicated.
- Chloramphenicol may also be used to treat the infection.
- Quinolone antibiotics have been given to treat this infection but there have been reports of treatment failure, as there have rarely for erythromycin and other macrolides.
- Patients who have severe disease may need to be managed in high dependency or intensive treatment units and given intravenous fluids, respiratory support and cardiovascular support.
- Acute respiratory failure
- Glomerulonephritis/tubulointerstitial nephritis
- Haemolytic anaemia
- Disseminated intravascular coagulation
- Reactive arthritis
- Transverse myelitis
- Guillain-Barré syndrome
- Arterial embolism
- Relapse of disease after antibiotic therapy
- Gestational psittacosis
Good, if recognised, and if early appropriate antibiotic therapy is given, mortality is as low as 1%. If undiagnosed and untreated, mortality can be as high as 15%.
- Regulation of the international bird trade with strict import controls.
- Education of bird owners, pet retailers and those who work with birds to be aware of the problem. Pet retailers should ideally keep a record of who purchases recently imported birds so that their owners can be contacted should there be an outbreak of the disease in the retail premises. This is good practice but there is no statutory duty to do so.
- Awareness of the diagnosis amongst the medical and veterinary professions.
The reference laboratory for psittacosis is now in Bristol (Bristol Regional HPA Laboratory) and details are available on the HPA website.
Further reading & references
- Community management of lower respiratory tract infection in adults, Scottish Intercollegiate Guidelines Network - SIGN (2002)
- Chest infections - adult, Clinical Knowledge Summaries (2007)
- File T et al; Guidelines for empiric antimicrobial prescribing in community-acquired pneumonia.; Chest 2004 May;125(5):1888-901.[abstract]
- Thibodeau KP, Viera AJ; Atypical pathogens and challenges in community-acquired pneumonia. Am Fam Physician. 2004 Apr 1;69(7):1699-706.
- Oba Y, Chlamydial Pneumonias, Medscape, Mar 2011; overview of infection with the three main chlamydial species that cause respiratory disease in humans
- MJ Bono, Mycoplasmal Pneumonia, Medscape, Mar 2011; concise overview from A&E perspective
- Psittacosis, Aberdeenshire Council; Information for bird owners
- Psittacosis, American Cockatiel Society; Information for bird owners
- Johnson SR, Pavord ID; Grand Rounds - City Hospital, Nottingham. A complicated case of community acquired pneumonia. BMJ. 1996 Apr 6;312(7035):899-901.
- American Veterinary Medical Association; Compendium of measures to control Chlamydophila psittaci (formerly Chlamydia psittaci) infection among humans (psittacosis) and pet birds, 2005
- Mayon-White R; Pets - pleasures and problems. BMJ. 2005 Nov 26;331(7527):1254-5.
- Lessnau K-D; Psittacosis, eMedicine, Jun 2008
- Psittacosis, Health Protection Agency
- Psittacosis, Centers for Disease Control and Prevention
- Macfarlane JT, Miller AC, Roderick Smith WH, et al; Comparative radiographic features of community acquired Legionnaires' disease, pneumococcal pneumonia, mycoplasma pneumonia, and psittacosis. Thorax. 1984 Jan;39(1):28-33.
- Geens T, Dewitte A, Boon N, et al; Development of a Chlamydophila psittaci species-specific and genotype-specific real-time PCR. Vet Res. 2005 Sep-Dec;36(5-6):787-97.
- Heddema ER, Beld MG, de Wever B, et al; Development of an internally controlled real-time PCR assay for detection of Chlamydophila psittaci in the LightCycler 2.0 system. Clin Microbiol Infect. 2006 Jun;12(6):571-5.
- Sareyyupoglu B, Cantekin Z, Bas B; Chlamydophila psittaci DNA detection in the faeces of cage birds. Zoonoses Public Health. 2007;54(6-7):237-42.
- Hyde SR, Benirschke K; Gestational psittacosis: case report and literature review. Mod Pathol. 1997 Jun;10(6):602-7.
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Dr Richard Draper
Dr Richard Draper