Chlamydophila Psittaci Laboratory Case Definition (LCD)

The Public Health Laboratory Network have developed a standard case definition for the diagnosis of diseases which are notifiable in Australia. This page contains the laboratory case definition for Chlamydophila Psittaci.

Page last updated: 17 November 2015

PDF printable version of Chlamydophila Psittaci Laboratory Case Definition (PDF 114 KB)

Version: 1.0
Authorisation: PHLN
Consensus Date: November 2015

1 PHLN Summary Laboratory Definition

1.1 Condition:

Psittacosis or Ornithosis

1.2.1 Definitive Laboratory Criteria

  • Isolation of Chlamydophila psittaci from a respiratory specimen (e.g., sputum, BAL, pleural fluid or lung tissue), OR
  • Detection of C. psittaci DNA in a respiratory specimen (e.g., sputum, BAL, pleural fluid or lung tissue) via polymerase chain reaction (PCR) assay, OR
  • Fourfold or greater increase in antibody (Immunoglobulin G [IgG]) against C. psittaci demonstrated by micro-immunofluorescence (MIF) or complement fixation (CF) assays between paired acute - and convalescent - phase serum specimens obtained at least 2 weeks apart in those older than 5 years with a clinically compatible illness.

1.2.2 Suggestive Criteria

  • A single high antibody titre against C. psittaci demonstrated by MIF, EIA or CF assays in a serum specimen obtained after onset of symptoms in those older than 5 years with a clinically compatible illness.

2 Introduction

2.1 The organism

Psittacosis (also known as parrot disease, parrot fever, and ornithosis) is a zoonotic disease caused by an obligate intracellular bacterium Chlamydophila psittaci (Chlamydia psittaci prior to 1999).1 This species includes six avian serovars, designated A to F, and two mammalian strains (M56 and WC).2 Sequenced C. psittaci genomes possess a single chromosome of approximately 1.1Mb and a conserved plasmid of ~8Kb containing 7-8 protein-coding sequences. The currently accepted ompA genotypes (A-F, E/B, M56 and WC) largely correspond to serovars and are distinguished by gene sequencing or genotype specific PCR. Genotypes A and B have been associated with psittacine birds and pigeons, respectively. Genotype C has been isolated primarily from ducks and geese, whereas genotype D was mainly found in turkeys. Genotype F was associated with infection in both turkeys and psittacine birds. The host range of genotype E is the most diverse (e.g., pigeons, ducks, turkeys). WC and M56 have been endemic in cattle and muskrats.2

C. psittaci bacteria are heat labile and killed at 560C for 30 minutes. They are also killed by common disinfectants; however, they withstand dessication for months.

2.2 The disease

Chlamydia (or Chlamydophila) causes oculogenital disease (C. trachomatis) or respiratory and systemic infections (C. pneumoniae and C. psittaci). Avian chlamydiosis refers to disease caused by C. psittaci in birds. This infection can occur in at least 460 bird species, spanning 30 different bird orders. The severity of disease in birds can range from mild to fatal disease. Infected birds may show signs of lethargy, anorexia, ruffled feathers, ocular/nasal discharge and diarrhoea. Antibiotic treatment is available for infected birds, but is prolonged (minimum 7 weeks of weekly injections, or oral treatment) and may be ineffective if the organism is in a dormant phase. Birds also do not develop protective immunity and, as a result, may become reinfected. C. psittaci can also infect mammals such as sheep, goats and cattle, causing chronic infection of the reproductive tract, placental insufficiency and abortion in these animals.3

Infection in humans usually manifests with ‘flu-like’ illness such as fever, chills, headaches, myalgias and dry cough. Breathlessness and chest tightness often accompany dry cough, and splenomegaly and rash may be present. The incubation period is usually 5-14 days, although periods of up to one month have been reported.3 Severity of infection can range from asymptomatic illness to systemic illness with severe pneumonia.4,5 Mortality rates of 15-30% were reported in the pre-antibiotic era although the disease is rarely fatal now. Chest radiograph findings include lobar or interstitial infiltrates.

Differential diagnoses of psittacosis include pneumonia due to other atypical infections such as Coxiella burnetti, the causative agent of Q fever, Mycoplasma pneumoniae, Chlamydia pneumoniae, Legionella species or respiratory viruses such as human influenza virus. C. psittaci has been reported to cause infection in other organ systems including endocarditis, myocarditis, hepatitis, arthritis, keratoconjunctivitis, and encephalitis. Severe disease, including fetal deaths have been reported when infection has occurred in pregnancy.5-8

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2.3 Transmission

C. psittaci can be transmitted to people exposed to birth fluids and placentas of infected animals. Human to human transmission has been suggested, but not proven.9 Infection due to C. psittaci in humans usually occurs through inhalation of aerosolised organisms from dried faeces or respiratory secretions, which can occur through mouth-to-beak contact or from handling infected birds. Pet birds such as parrots, parakeets, macaws, cockatiels, and poultry birds such as turkeys and ducks are most frequently involved in transmission to humans.1,3 Infected birds shed the bacteria through faeces and nasal discharges, which can remain infectious for several months. Infection can occur after brief exposures, and therefore patients may not always recall a definitive history of contact with birds.1,3,10,11 Veterinarians, bird breeders and animal shopkeepers are at particular risk. In addition, activities such as gardening and moving or trimming lawns without a grass catcher have been associated with human psittacosis.12

3 Laboratory Diagnosis / Tests

3.1 Bacterial culture

C. psittaci can be isolated by using cell culture method, although the procedure is not used for routine diagnostic purposes and only performed in reference laboratories. C. psittaci is a Biosafety Level 3 pathogen, and transmission of the organisms from patient specimens or infected cell cultures can occur though aerosolisation or splashes onto mucous membranes. Culture, when required, is time consuming and only performed in laboratories with a physical containment 3 facility.

3.1.1 Suitable specimen

Respiratory specimen including broncho-alveolar lavage and sputum are suitable specimens for C. psittaci cultures.

3.1.2 Media

A number of cell lines can be used to isolate chlamydiae from clinical specimens, including McCoy, HeLa 229, Hep-2, BGMK, Vero and L cells. Cultures are incubated for 48-72 hours in the presence of host cell protein synthesis inhibitor cycloheximide. A positive culture is confirmed though the presence of typical intracytoplasmic inclusions seen after immunostaining.8

3.1.3 Test sensitivity and specificity

There are no data available on sensitivity and specificity of culture as it is rarely done as a part of routine diagnosis and there is no test that is considered to be the ‘gold standard’ for diagnosis of psittacosis. The use of C. psittaci 6BC (ATCC VR-125, bird isolate) and Orni strain (human isolate) as controls is encouraged.

3.2 Serology

Serology remains the mainstay for diagnosis of C. psittaci infection, however, it can be prone to false-positive and false-negative results. The surface located antigens, such as chlamydial lipopolysaccharide, can cross-react with antibodies to other bacteria. Timely treatment with appropriate antibiotics may inhibit the development of detectable antibodies. The most commonly used serologic formats include recombinant enzyme linked immunosorbent assays (rELISA), complement fixation test (CFT) and microimmunofluoresence test (MIF) to detect immunoglobulin M (IgM), IgG and IgA antibodies with either family, serotype or species specificity. Paired acute and convalescent serologic samples taken 10-14 days apart are preferred for diagnosis.

3.2.1 Recombinant ELISA

The recombinant ELISA is genus reactive and provides advantages of automation and objectivity for screening all requests for respiratory infection related chlamydia (C. pneumoniae and C. psittaci). Kits for rELISA utilise purified recombinant lipopolysaccharide. Anti-LPS antibody usually develops rapidly after the onset of infection; whereas MIF response is often delayed. Serologic testing for Chlamydia-specific IgG and IgA is often used to screen specimens prior to the more laborious MIF testing. Presence of IgG with a negative IgA indicates past infection, whereas the presence of both IgG and IgA or solitary IgA most likely indicates recent infection or a false positive IgA; repeat testing is indicated 10-14 days later to demonstrate IgG seroconversion or rising IgG titre.

3.2.2 Complement fixation test (CFT)

The complement fixation test can be used for serologic diagnosis of psittacosis. The test is based on antibody reactivity to the chlamydial LPS antigen common to all members of the Chlamydiaceae. Cross-reactivity can occur with other members of the Chlamydiaceae and titre above 1:16 can be interpreted as evidence of past or recent chlamydial infection.

3.2.3 Microimmunofluorescence test (MIF)

The microimmunofluorescence test is considered the method of choice for the confirmatory step for serologic diagnosis of Chlamydial infections. Species and serovar-specific antibody responses can be detected by using this method. Purified elementary bodies (EBs) of representative strains of C. psittaci are dotted in a specific pattern onto glass slides. Serial dilutions of patient sera are placed over the fixed antigen dots and incubated, and bound antibody is detected with fluorescein-conjugated anti-IgG or anti-IgM antibody. The MIF assay format is technically demanding, time-consuming and may be less suited for higher volume testing. Single titres greater than 32 or a four-fold rise in titre between acute and convalescent specimen are suggestive of acute infection. The performance of the test depends on several factors, including the antigen preparations used and the experience of the person reading the test.8

3.2.4 Quality Assurance

Laboratories performing Chlamydia serology participate in Quality Assurance Program organised by the Royal College of Pathologists of Australasia.

3.2.5 Test sensitivity and specificity

There are no data available on sensitivity and specificity of serology as there is no one test that is considered to be ‘gold standard’ for diagnosis of psittacosis.

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3.3 Nucleic acid amplification tests (NAAT)

Given the limited specificity of serology testing due to the high prevalence of C. pneumoniae infection in humans, nucleic acid amplification based testing targeting divergent genetic targets, such ompA gene, has been developed.

3.3.1 Suitable specimen

Sputum, throat swabs and bronchoalveolar lavage are the most commonly used specimens for NAAT. Blood, urine, CSF and occasionally environmental specimens can also be used.

3.3.2 Procedure

NAAT using genus specific and species specific sequences can be used to detect the Chlamydia genus and to speciate into C. pneumoniae and C. psittaci. NAAT has been based on MOMP gene (major outer membrane protein) and the 23S rRNA gene for genus and IncA gene and 16-23S rRNA interspacer region for C.psittaci species. The second step of PCR is species specific and discriminates between different Chlamydia species. Amplicons are detected using SYBR green and melt curve analysis and confirmed with gel electrophoresis.8,13

3.3.3 Test sensitivity and specificity

There are no data available on sensitivity and specificity of serology as there is no one test that is considered to be the ‘gold standard’ for diagnosis of psittacosis.

3.4 Strain subtyping

Similarity of C. psittaci can be assessed by restriction fragment length polymorphism of ompA gene on isolates or PCR amplicons. Multiple loci variable number of tandem repeats (VNTR) analysis (MLVA) based on the detection of tandem repeat polymorphisms of eight loci has been described.14 MLVA analysis can be performed directly on DNA extracted from clinical specimens, however, the inter-strain discriminatory power of C. psittaci molecular typing is not fully understood.

4 Snomed-CT Terminology

SNOMED CT concept Code
Psittacosis/ornithosis (disorder)
Chlamydophila psittaci (organism)
Chlamydia psittaci culture (procedure)
Polymerase chain reaction analysis (procedure)
Chlamydia group complement fixation test (procedure)
Chlamydia psittaci IgG level (procedure)
Chlamydia psittaci IgA level (procedure)
Chlamydia psittaci IgM level (procedure)
Chlamydia psittaci antibody level (procedure)
Microbial antibody titer by immunofluorescence method (procedure)
Polymerase chain reaction analysis for genomic fingerprinting (procedure)
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5 References

  1. Centers for Disease Control and Prevention. National Notifiable Diseases Surveillance System (NNDSS). Psittacosis/Ornithosis (Chlamydophila psittaci) 2010 Case Definition.
  2. Beeckman DSA, Vanrompay DCG. Zoonotic Chlamydophila psittaci infections from a clinical perspective. Clin Microbiol Infect 2009;15:11-17.
  3. Raso TF, Ferreira V L, Timm LN, Abreu FTM. Psittacosis domiciliary outbreak associated with monk parakeets (Myiopsitta monachus) in Brazil: need for surveillance and control. Journal of Medical Microbiology case reports 2014 doi: Microbiology Society
  4. Branley JM, Weston KM, England J, Dwyer DE, Sorrell T. C. Clinical features of endemic community-acquired psittacosis. New Microbes and New Infections 2014;2 (1):7-12.
  5. Pandeli V, Ernest D. A case of fulminant psittacosis. Crit Care Resusc 2006; 8: 40-42.
  6. Birkhead JS, Apostolov K. Endocarditis caused by psittacosis agent. British Heart Journal 1974; 36: 728-731.
  7. Cowie J, Chidley K, Hughes P. Neurological complications in psittacosis: a case report and literature review. Respiratory Medicine 1995; 89(9):637-38.
  8. Jorgensen JH, Pfaller MA, Carroll KC, Funke G, Landry ML, Richter SS et al. Manual of Clinical Microbiology, 11th Edition, ASM Press, Washington, D.C.
  9. Wallensten A, Fredlund H, Runehagen A. Multiple human-to-human transmission from a severe case of psittacosis, Sweden, January–February 2013. Euro Surveill 2014;19(42).
  10. Telfer BL, Moberley SA, Hort KP, Branley JM, Dwyer DE, Muscatello DJ et al. Probable psittacosis outbreak linked to wild birds. Emerg Infect Dis 2005; 11(3): 391–397.
  11. Rehn M, Ringberg H, Runehagen A, Herrmann B, Olsen B, Petersson AC et al. Unusual increase of psittacosis in southern Sweden linked to wild bird exposure, January to April 2013. Euro Surveill 2013;18(19).
  12. Williams J, Tallis G, Dalton C, et al. Community outbreak of psittacosis in a rural Australian town. Lancet 1998;351:1697-99.
  13. Schuller M, Sloots TP, James GS, Halliday CL, Carter IJW. In: PCR for Clinical Microbiology. An Australian and International Perspective. Springer, 2010.
  14. Laroucau K, Thierry S, Vorimore F, Blanco K, et al. High resolution typing of Chlamydophila psittaci by multilocus VNTR analysis (MLVA). Infect Genet Evol 2008;8:171-81.