Chlamydophila psittaci

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colspan=2 style="text-align: center; background-color: transparent" | Chlamydophila psittaci
colspan=2 style="min-width:15em; text-align: center; background-color: transparent" | Scientific classification
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colspan=2 style="text-align: center; background-color: transparent" | Binomial name
Chlamydophila psittaci (Lillie 1930) Everett et al. 1999

Chlamydophila psittaci is a species of bacteria that belongs to the family Chlamydiaceae. It is an obligate intracellular pathogen, meaning it can only reproduce within the cells of a host organism. C. psittaci is primarily known for causing psittacosis, also known as parrot fever, which is a zoonotic infectious disease that can be transmitted from birds to humans.

Taxonomy and Classification

Chlamydophila psittaci was originally classified under the genus Chlamydia, but was reclassified into the genus Chlamydophila in 1999. This reclassification was based on genetic and phenotypic differences that warranted a distinction from other Chlamydia species. However, recent taxonomic revisions have suggested merging Chlamydophila back into Chlamydia.

Morphology and Life Cycle

C. psittaci is a small, gram-negative bacterium that exhibits a unique biphasic developmental cycle. It exists in two forms:

• Elementary bodies (EBs): These are the infectious form of the bacterium, which are metabolically inactive and can survive outside host cells. EBs are responsible for the transmission of the bacterium from one host to another.

• Reticulate bodies (RBs): Once inside a host cell, EBs transform into RBs, which are metabolically active and capable of replication. RBs divide by binary fission within a membrane-bound vacuole called an inclusion.

The cycle concludes when RBs convert back into EBs, which are then released from the host cell to infect new cells.

Epidemiology

C. psittaci is primarily associated with birds, particularly psittacine birds such as parrots, parakeets, and cockatiels. However, it can also infect a wide range of avian species, including pigeons, ducks, and turkeys. Human infection typically occurs through inhalation of aerosolized particles from dried bird droppings, feathers, or respiratory secretions.

Clinical Manifestations

In humans, C. psittaci infection can range from mild flu-like symptoms to severe pneumonia. Common symptoms include:

• Fever
• Chills
• Headache
• Muscle aches
• Dry cough
• Shortness of breath

In severe cases, complications such as endocarditis, hepatitis, and encephalitis may occur.

Diagnosis

Diagnosis of psittacosis can be challenging due to its nonspecific symptoms. Laboratory tests used for diagnosis include:

• Polymerase chain reaction (PCR) assays to detect bacterial DNA
• Serological tests to identify antibodies against C. psittaci
• Culture of the bacterium from respiratory secretions or tissue samples

Treatment

The primary treatment for psittacosis is antibiotic therapy. Tetracyclines, such as doxycycline, are the antibiotics of choice. In cases where tetracyclines are contraindicated, macrolides such as azithromycin may be used.

Prevention

Preventive measures focus on reducing exposure to infected birds. These include:

• Proper handling and care of pet birds
• Regular cleaning and disinfection of bird cages
• Use of protective equipment when handling birds or cleaning bird habitats

See Also

• Chlamydia (genus)
• Zoonosis
• Pneumonia

References

• Everett, K. D. E., Bush, R. M., & Andersen, A. A. (1999). Emended description of the order Chlamydiales, proposal of Parachlamydiaceae fam. nov. and Simkaniaceae fam. nov., each containing one monotypic genus, revised taxonomy of the family Chlamydiaceae, including a new genus and five new species, and standards for the identification of organisms. International Journal of Systematic Bacteriology, 49(2), 415-440.
• Longbottom, D., & Coulter, L. J. (2003). Animal chlamydioses and zoonotic implications. Journal of Comparative Pathology, 128(4), 217-244.