What Is Psittacosis?

  • Dr Kinza Asim Master of Science in Medical Research, University of Leicester, UK

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Introduction

Psittacosis (also known as parrot fever) is a disease that affects humans who come into contact with affected birds. The disease is caused by Chlamydia psittaci and is usually transmitted by breathing in the dust of bird faecal matter. It is important to remember that most birds that are infected with Chlamydia psittaci will not show any symptoms, so adequate care needs to be taken when handling domesticated or wild birds.  Human-to-human transmission of the disease has been reported, but it is thought to be very rare. It has also been found that some people can be asymptomatic carriers (they show no symptoms of the disease but are still infected with Chlamydia psittaci).2 

Historical background

In the 1930s, there were lots of outbreaks of psittacosis, causing widespread death. Respiratory diseases were associated with the importation of parrots. It was then discovered that the pattern of infection was directly related to people who had come into contact with birds infected with Chlamydia psittaci, and this is a reported case of zoonosis when an animal transmits a bacteria to humans.1  

Clinical manifestations

  • Cough 
  • Difficulty breathing 
  • Fever and chills 
  • Headache 

Severity and complications

There is a huge spectrum when it comes to the severity of symptoms. Some people may have very mild or no symptoms at all, and others may have severe breathing difficulty due to psittacosis infection. If left untreated, complications such as inflammation of the heart and/or the brain can occur. Hepatitis is also another common complication of psittacosis.7

Epidemiology

There are a greater number of cases in tropical climates; however, the condition can be found across the globe. “A 1982 survey, C. psittaci was isolated from 20-50% of necropsied pet birds in California and Florida.”8 High-risk groups for psittacosis are people who work with birds in the parrot family. Also, people who process turkey and other birds are at a greater risk of getting psittacosis. 

The global spread of the disease is directly related to areas that have a higher incidence of infected bird species. Types of birds associated with C.psittaci:

  • Turkeys, pigeons, and ducks
  • Parrots and parakeets
  • Cockatiels and canaries

Diagnosis

A clinical evaluation of presenting symptoms is first required to determine whether a patient has psittacosis. Unfortunately, many symptoms of psittacosis will overlap with other respiratory diseases, and as such, further laboratory tests will be required for a definitive diagnosis. These fall into two main categories: serologic testing and polymerase chain reaction (PCR). Usually, people show symptoms within 10 days; however, the incubation period can be up to 4 weeks.9 C. psittaci is a Gram-negative bacteria, which means that we can use Gram staining to help decide on whether there is a diagnosis of psittacosis. 

Methods used to determine a diagnosis of psittacosis

  • Giemsa staining for Chlamydia psittaci5
  • Serology - testing for antibodies against Chlamydia psittaci in the serum of the patient is useful to determine if the person has antibodies to the bacteria. However, this is not always very useful as the patient may have antibodies to the bacteria, but not be in a current active infection. Therefore, molecular testing can be used in conjunction with serology testing to confirm a diagnosis alongside a comprehensive clinical history of the patients working with avian populations.
  • ELISA is a type of serological testing used in clinical laboratories to test for psittacosis infection11,12
  • Staining with methyl green and neutral red - this is considered a better method than Giemsa staining6
  •  Microimmunofluorescence - Fluorescent antibodies can also be used to determine whether there are inclusions of psittacosis 
  • PCR - this is a molecular test that can be done on respiratory swabs that have been placed in a liquid. The liquid is then tested for the presence of the bacteria. PCR has a very high sensitivity, and samples can also be batched for quicker turnaround times on results. The downside of PCR testing in psittacosis diagnosis is that the equipment is not available in all clinical diagnostic laboratories.

Genotyping 

In order to map the spread of different strains of the bacteria, scientists will use genotyping methods to determine the different strains of psittacosis.11 These methods include:

  • MLST
  • PCR-RFLP
  • DNA microarrays 
  • Next-generation DNA sequencing11

Treatment and management

The main treatment option for psittacosis is antibiotics. The two main groups of antibiotics that work in patients with psittacosis are macrolides and tetracyclines. It is usually not recommended to use tetracyclines in children younger than 8 years of age. Severe respiratory symptoms should initially be treated with doxycycline. Prompt treatment with antibiotics is essential to reduce the likelihood of complications and exacerbation of symptoms. Management of severe symptoms may include breathing support if the lungs have become inflamed. Another main symptom is fever, and as such, paracetamol can be given to reduce the patient's temperature.3

Prevention strategies

Occupational safety when working with domesticated birds, or birds for human consumption, is important to reduce the transmission of the bacteria to humans. The reporting and surveillance of any outbreaks are important to enable a reduction in the transmission of the bacteria.  One of the important facts about C. psittaci is that it has an inactive elementary body (EB) and also a reticulate body (RB). This means that the bacteria can survive outside of a host (for example, in faecal droppings). Essentially this life cycle of having an inactive and active form means that you can’t grow C. psittaci in standard bacterial growth medium, and as such alternative culture methods are required.10

Containment strategies

Containment strategies and outbreak control measures involve preventing overcrowding of birds and ensuring cages are kept clean as the droppings transmit the bacteria. It is also important to use solid bases in the cage to prevent faecal matter from going from one cage to the next. It is also important to isolate any birds that are showing symptoms of being unwell in any way to reduce the likelihood of more animals becoming infected.4

Awareness and education

There is a connection between animal and human health. To prevent human disease, we also need to prevent the disease in the avian population. Therefore, the role of veterinary medicine in psittacosis prevention is important to reduce the likelihood of a zoonotic infection. Collaborative approaches for disease control between different agencies are also important for maintaining health in both humans and birds. Future challenges involve emerging strains and variants that are resistant to antibiotic therapy. 

Vaccine development 

There is currently no vaccine for psittacosis, however, if a vaccine were to be made commercially available this would reduce the likelihood of people becoming infected with the bacteria. Ideally, people who come into close contact with birds could become vaccinated, preventing onward disease transmission (even though person-to-person transmission is rare). 

Conclusion

In conclusion, psittacosis is a disease caused by the transmission of psittacosis bacteria from animals to humans. Preventing the disease is associated with maintaining good levels of h hygiene when handling infected birds, and usually, the condition can be managed with antibiotic treatment. It is important to have prompt treatment due to the likelihood of complications if the infection remains untreated such as inflammation of the heart. It is important to raise awareness so that people handling birds are aware of the possibility of psittacosis infection and ways to prevent infections from occurring, such as reducing overcrowding of birds. 

References

  1. Weston KM, Polkinghorne A, Branley JM. Psittacosis contagion in 1930: an old story in a new era of zoonotic disease. Microbes Infect. 2023;25(4):105076. doi:10.1016/j.micinf.2022.105076
  2. Zhang Z., Zhou H., Cao H., Ji J., Zhang R., Li W., et al. Human-to-human transmission of Chlamydia psittaci in China, 2020: an epidemiological and aetiological investigation. Lancet Microbe. 2022;(3):e512–e520
  3. https://www.cdc.gov/pneumonia/atypical/psittacosis/hcp/diagnosis-treatment-prevention.html#:~:text=Chlamydia%20psittaci%20are%20sensitive%20to,due%20to%20reported%20macrolide%20failures.
  4. Balsamo G, Maxted AM, Midla JW, Murphy JM, Wohrle R, Edling TM, et al. Compendium of Measures to Control Chlamydia psittaci Infection Among Humans (Psittacosis) and Pet Birds (Avian Chlamydiosis), 2017. Journal of Avian Medicine and Surgery. 2017 Sep;31(3):262–82.
  5. Pearson JE, Gustafson GA, Senne DA, Peterson LA. Isolation and identification of Chlamydia psittaci from pet birds. J Am Vet Med Assoc. 1989;195(11):1564-1567.
  6. Woodland RM, Malam J, Darougar S. A rapid method for staining inclusions of Chlamydia psittaci and Chlamydia trachomatis. J Clin Pathol. 1982;35(6):642-644. doi:10.1136/jcp.35.6.642
  7. Samra Z, Pik A, Guidetti-Sharon A, Yona E, Weisman Y. Hepatitis in a family infected by Chlamydia psittaci. J R Soc Med. 1991;84(6):347-348. doi:10.1177/014107689108400614
  8. https://www.nj.gov/agriculture/divisions/ah/diseases/psittacosis.html
  9. “Avian Chlamydiosis.” In Whiteman and Bickford’s Avian Disease Manual, 4th ed. Edited by B.R. Charlton et al. Kennett Square, Pa: American Association of Avian Pathologists, 1996, pp. 68-71.
  10. AbdelRahman, Y.M.; Belland, R.J. The chlamydial development cycle. FEMS Microbiol. Rev. 2016, 29, 949–959. 
  11. World Organization for Animal Health (OIE). Manual of diagnostic tests and vaccines for terrestrial animals [online]. Paris: OIE; 2015. Avian chlamydiosis. Available at: http://www.oie.int/fileadmin/Home/eng/Health_standards/tah m/2.03.01_AVIAN_CHLAMYD.pdf. Accessed 21/11/2023
  12. Lewis VJ, Thacker WL, Mitchell SH. Enzyme-linked immunosorbent assay for chlamydial antibodies. J Clin Microbiol. 1977;6(5):507-510. doi:10.1128/jcm.6.5.507-510.1977

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