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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, budgerigars, cockatoos and lories. A large number (>100) of avian species such as canaries, doves, 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) it can affect humans working with these animals. Whether human-to-human transmission occurs is debatable. If it does, it is extremely rare.
- 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. The Health Protection Agency (HPA) states around 50 cases are confirmed in England and Wales each year, but that it is likely to be under-diagnosed.
- The HPA requests that they be informed of any cases, particularly those connected with pet retailers.
- Working in, or buying from, a pet shop. Psittacosis is the most common zoonosis acquired through a pet shop according to a recent study of available literature.
- Pet bird ownership.
- Pigeon fancying.
- Contact with ill birds.
- Certain occupations:
- Poultry farmers.
- Poultry processing plant workers.
- Bird breeders and those selling birds.
- Zoo and bird park keepers.
- Street cleaners.
- Those working on building demolition or conservation where birds have been nesting.
The incubation period is 1-4 weeks. Most infections become symptomatic in 5-14 days.
- Classically, it presents as a community-acquired pneumonia with flu-like symptoms. There are marked signs of systemic illness/constitutional upset. Fever and lassitude are common. It may develop mildly and insidiously or develop into overwhelming sepsis with acute respiratory failure.
- Respiratory symptoms include a non-productive cough, dyspnoea, sore throat, nosebleeds 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 (Horder's spots) with an 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's 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.
- Hypersensitivity pneumonitis - formerly know as 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 four-fold rise in antibody titre between acute and convalescent sera. These paired sera (blood samples collected two weeks apart) are tested for chlamydial antibodies. Unfortunately, this means the diagnosis is delayed. High titres can occur in other chlamydial infections, so if history suggests psittacosis, molecular assays (PCR) are used to diagnose C. psittaci infection.
- 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.
- 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.
- Relapse of disease after antibiotic therapy.
- Acute respiratory failure.
- Glomerulonephritis/tubulointerstitial nephritis.
- Haemolytic anaemia.
- Disseminated intravascular coagulation.
- Reactive arthritis.
- Transverse myelitis.
- Guillain-Barré syndrome.
- Arterial embolism.
- Gestational psittacosis.
Good, if recognised, and if early appropriate antibiotic therapy is given, it is rarely fatal. 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.
- Infection prevention advice to those handling birds including:
- Good ventilation in bird housing.
- Isolation of new or sick birds.
- Regular cleaning of birdcages to avoid faeces drying.
- Cleaning procedures should avoid creating aerosols and dust (eg, avoid high-pressure jet washing).
- Protective clothing should be worn when removing dried faeces or in poultry processing plants.
- Use of disinfectants.
- Good hygiene practices.
The reference laboratory for psittacosis is the Bristol Regional HPA Laboratory - see the Public Health England link below.
Further reading and references
Thibodeau KP, Viera AJ; Atypical pathogens and challenges in community-acquired pneumonia. Am Fam Physician. 2004 Apr 169(7):1699-706.
Mayon-White R; Pets - pleasures and problems. BMJ. 2005 Nov 26331(7527):1254-5.
Psittacosis; The Parrot Society UK
Psittacosis; Public Health England
Halsby KD, Walsh AL, Campbell C, et al; Healthy animals, healthy people: zoonosis risk from animal contact in pet shops, a systematic review of the literature. PLoS One. 2014 Feb 269(2):e89309. doi: 10.1371/journal.pone.0089309. eCollection 2014.
Psittacosis; Health and Safety Executive (HSE)
Psittacosis/Avian Chlamydiosis; The centre for food security & public health, and the Institute for international cooperation in animal biologics. College of vetinary medicine, Iowa State University. Updated 2009.
UK Standards for microbiological investigations. Chlamydial zoonotic infections; Public Health England (PHE), 2013
Stewardson AJ, Grayson ML; Psittacosis. Infect Dis Clin North Am. 2010 Mar24(1):7-25. doi: 10.1016/j.idc.2009.10.003.
Janssen MJ, van de Wetering K, Arabin B; Sepsis due to gestational psittacosis: A multidisciplinary approach within a perinatological center--review of reported cases. Int J Fertil Womens Med. 2006 Jan-Feb51(1):17-20.