Psittacosis

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 1929–30, 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 can rarely 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,¹ however some experts dispute that this occurs.²

• 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 (e.g. giving resuscitation) and from handling plumage or infected tissues.²
• The organism is resistant to drying and can survive for several months in bird dander or faeces.
• The inoculum enters the blood stream 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 2005.²
• It is thought there is a significant amount of under-diagnosis and under-reporting based on population sero-surveillance studies.² The HPA request that they be informed of any cases, particularly those connected with pet retailers.²

Risk factors

Working with birds, pet bird ownership, pigeon fancying, contact with ill birds.

The incubation period is 5–19³ days but some estimate it may be as long as 28 days.² There has been a case with an observed incubation period of 54 days.¹

Symptoms

• Classically presents as a community-acquired pneumonia with flu-like symptoms.² 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 non-productive 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 common is 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).

Signs

• There may be signs of pneumonic consolidation, but often the chest examination is rather non-specific 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)
• Other atypical pneumonias, eg legionella, mycoplasma
• Q fever
• Infective endocarditis
• Bacterial pneumonia
• Viral pneumonia
• Tuberculosis
• Tularaemia
• Typhoid
• 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.⁴
• Culture of C. psittaci is usually avoided due to its hazardous nature.
• Diagnosis is usually confirmed by the presence of a 4-fold rise in antibody titre between acute and convalescent sera. These paired sera (blood samples collected two weeks apart) are tested for chlamydial antibodies.
• PCR and microimmunofluorescence techniques are being developed but currently remain experimental.^5,6
• ELISA testing has been used to confirm the diagnosis.
• Infection in birds can be detected using PCR based testing kits.⁷

• 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 contraindicated.
• 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 on HDU or ITU and given intravenous fluids, respiratory and cardiovascular support.

• Acute respiratory failure
• Endocarditis
• Pericarditis
• Myocarditis
• Glomerulonephritis/tubulo-interstitial nephritis
• Haemolytic anaemia
• DIC
• Pancreatitis
• Reactive arthritis
• Transverse myelitis
• Meningoencephalitis
• Guillain-Barré syndrome
• Arterial embolism
• Relapse of disease after antibiotic therapy
• Gestational psittacosis⁸

Good if recognised and early appropriate antibiotic therapy given with mortality 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

Contact details for HPA to report cases Robert Smith, Zoonoses Surveillance Unit, National Public Health Service for Wales, Communicable Disease Surveillance Centre; tel: 029 20 521997, fax: 029 20 521987, email:robert.smith@nphs.wales.nhs.uk