A 70 y.o. farmer presents with high fever and cough
He recently acquired six chickens and ducks.
what is in your differential?
Our patient had an atypical pneumonia caused by Chlamydia psittaci . A large epidemic occurred in the 1930s which was traced to Argentinian parrots. While it was named for parrots, it occurs in many animals including dogs, cats, horses and wallabies . It is a Gram negative intracellular parasite.
argentinian green parrots were sold in the UK and US
Remember the types of Chlamydia that cause human disease
C. psittaci causes ornithosis after exposure to an infected bird. The clinical presentation can range from asymptomatic infection to a fulminant toxic syndrome. The most common presentation is fever.
C pneumoniae causes an atypical pneumonia usually in children or adolescents. Most people are exposed to C pneumoniae in their lifetime. Approximately one-half of the population has C pneumoniae antibodies by age 20 years, and an estimated 80% of adults older than age 60 years have these antibodies. Most people recover in seven to ten days after infection It presents with fever cough and lower respiratory tract infection. Extrapulmonary symptoms are also possible with reactive arthritis, erythema nodosum , thyroiditis and Guillain Barre syndrome. Rarely myocarditis and encephalitis occur. While chlamydia accounts for only 1% of community acquired pneumonia cases this may be because it is underdiagnosed.
C. trachomatis -is the cause of sexually transmitted diseases. It can however, cause pneumonia in children and eye infections in developing countries. It is a leading cause of infectious blindness in Africa.
trachoma begins on the conjunctiva which lines the eyelid
it progresses to the cornea where it can cause blindness
In our patient Chlamydia psittaci was found in his alveolar lavage fluid through targeted next-generation sequencing testing for respiratory pathogens . This technique sequences all nucleic acids in a sample allowing for the detection of known, unexpected, or emerging pathogens. This is much faster than culturing a sample. In this case outer membrane protein A was detected in poultry feces which was identical to the specimen from the patient.
Our patient was treated with doxycycline and moxifloxacin and recovered. In the US both macrolides and doxcycline are recommended.
THE DIFFERENTIAL
The differential for atypical pneumonia includes mycoplasma pneumoniae, legionella, Francisella tularensis and Coxiella burnetii. Fungal pneumonia or viral pneumonia should also be considered.
FUN FACTS
The term psittacosis is derived from the Greek word for parrot, psittakos and was first used in 1892 to describe a febrile illness in humans. Ornithosis is the term used to describe the same disease in nonpsittacine birds, like chickens.
In Africa chlamydia trachomatis is spread by Musca sorbens a species of fly that feeds on ocular and nasal discharge to obtain their nutrients. In areas with poor sanitation is is difficult to eradiate the fly.
Zeng Z, Han T, Huang L, Lin Z, Liu W, Liu J, Wu S, Xiao F. A Case of Psittacosis - Putian City, Fujian Province, China, April 2025. China CDC Wkly. 2025 Jul 18;7(29):985-986. doi: 10.46234/ccdcw2025.166. PMID: 40832062; PMCID: PMC12360314.
Huang WF, Wang FG, Cai QQ, Xu HL, Hong DW, Wu H, et al .Epidemiological and clinical characteristics of psittacosis among cases with complicated or atypical pulmonary infection using metagenomic next-generation sequencing: a multi-center observational study in China. Ann Clin Microbiol Antimicrob. 2023;22(1):80.
Ageed A, Khan M. Eliminating trachoma in Africa: the importance of environmental interventions. Cureus 2024 Jan 16;16(1)::e52358. doi:10.7759/cureus.52358
https://webeye.ophth.uiowa.edu/eyeforum/atlas/pages/trachoma.html#gsc.tab=0
Thylefors B, Dawson CR, Jones BR, West SK, Taylor HR. A simple system for the assessment of trachoma and its complications. Bull World Health Org, 1987; 65: 477-483.