Severe Chlamydophila psittaci pneumonia rapidly diagnosed by detection of antigen in sputum with an immunochromatography assay

Severe psittacosis progressing to suspected organizing pneumonia and the role of corticosteroids

Background

Psittacosis is a systemic disease usually with respiratory involvement, caused by the obligate intracellular bacterium Chlamydia psittaci. Exposure to birds, the main zoonotic reservoir, is a major risk factor for infection. The spectrum of disease is highly variable, ranging from subclinical infection to severe pneumonia requiring mechanical ventilation. There is limited data on psittacosis progressing to organizing pneumonia and management of such cases.

Case presentation

A 63-year-old man was referred to a rural hospital with 11 days of fevers to 39 °C, myalgia, lethargy and several days of dry cough. After initial treatment with benzylpenicillin and doxycycline for left lower pneumonia found on CXR, the patient deteriorated with extensive bilateral consolidation on chest CT requiring mechanical ventilation. Atypical pneumonia screening was negative, however, exposure to a sick bird prior to symptom onset triggered testing for C. psittaci which was positive. Doxycycline was recommenced with minimal benefit, and organizing pneumonia was later suspected. The patient slowly improved with a weaning course of corticosteroids started after 19 days and was discharged from hospital. He unfortunately was re-admitted and died several months later.

Conclusion

Severe pneumonia is a rare, but potentially life-threatening complication of psittacosis. We present a case of psittacosis which progressed to suspected organizing pneumonia despite appropriate antibiotics, and subsequent treatment with corticosteroids. This case suggests it may be useful to consider corticosteroids early in therapy for patients with severe psittacosis. Our paper underlines the need for further research to determine the best management of severe psittacosis to improve patient outcomes.

Comparative analysis of Chlamydia psittaci genomes reveals the recent emergence of a pathogenic lineage with a broad host range

Chlamydia psittaci is an obligate intracellular bacterium. Interest in Chlamydia stems from its high degree of virulence as an intestinal and pulmonary pathogen across a broad range of animals, including humans. C. psittaci human pulmonary infections, referred to as psittacosis, can be life-threatening, which is why the organism was developed as a bioweapon in the 20th century and is listed as a CDC biothreat agent. One remarkable recent result from comparative genomics is the finding of frequent homologous recombination across the genome of the sexually transmitted and trachoma pathogen Chlamydia trachomatis. We sought to determine if similar evolutionary dynamics occurred in C. psittaci. We analyzed 20 C. psittaci genomes from diverse strains representing the nine known serotypes of the organism as well as infections in a range of birds and mammals, including humans. Genome annotation revealed a core genome in all strains of 911 genes. Our analyses showed that C. psittaci has a history of frequently switching hosts and undergoing recombination more often than C. trachomatis. Evolutionary history reconstructions showed genome-wide homologous recombination and evidence of whole-plasmid exchange. Tracking the origins of recombinant segments revealed that some strains have imported DNA from as-yet-unsampled or -unsequenced C. psittaci lineages or other Chlamydiaceae species. Three ancestral populations of C. psittaci were predicted, explaining the current population structure. Molecular clock analysis found that certain strains are part of a clonal epidemic expansion likely introduced into North America by South American bird traders, suggesting that psittacosis is a recently emerged disease originating in New World parrots.

Chlamydia psittaci is classified as a CDC biothreat agent based on its association with life-threatening lung disease, termed psittacosis, in humans. Because of the recent remarkable findings of frequent recombination across the genome of the human sexually transmitted and ocular trachoma pathogen Chlamydia trachomatis, we sought to determine if similar evolutionary dynamics occur in C. psittaci. Twenty C. psittaci genomes were analyzed from diverse strains that may play a pathogenic role in human disease. Evolution of the strains revealed genome-wide recombination occurring at a higher rate than for C. trachomatis. Certain strains were discovered to be part of a recent epidemic clonal expansion originating in South America. These strains may have been introduced into the United States from South American bird traders, suggesting that psittacosis is a recently emerged disease originating in New World parrots. Our analyses indicate that C. psittaci strains have a history of frequently switching hosts and undergoing recombination.

Development potential of rifalazil and other benzoxazinorifamycins

Rifalazil and other benzoxazinorifamycins (new chemical entities [NCEs]) are rifamycins that contain a distinct planar benzoxazine ring. Rifalazil has excellent antibacterial activity, high intracellular levels and high tissue penetration, which are attributes that favour its use in treating diseases caused by the obligate intracellular pathogens of the genus Chlamydia. Recent studies have shown that rifalazil has efficacy in the treatment of human sexually transmitted disease caused by Chlamydia trachomatis. The extraordinary potency of rifalazil and other NCEs, such as ABI-0043, extends to the related microorganism, C. pneumoniae, a respiratory pathogen that can disseminate and persist chronically in the vasculature, resulting in increased plaque formation in animal studies. A pivotal clinical trial with rifalazil has been initiated for the treatment of peripheral arterial disease. Other opportunities include gastric ulcer disease caused by Helicobacter pylori and antibiotic-associated colitis caused by infection with Clostridium difficile in the colon. The NCEs could prove to be valuable as follow-on compounds in these indications, as rifampin replacements in antibacterial combination therapy or as stand-alone topical antibacterials (e.g., to treat acne). Neither rifalazil nor NCEs appear to induce the cytochrome P450 3A4, an attribute of rifampin that can result in adverse events due to drug-drug interactions.