A man with chills, fever, and headache is thought to have “atypical” pneumonia. History reveals that he raises chickens, and that approximately 2 weeks ago he lost a large number of them to an undiagnosed disease. Which of the following is the most likely diagnosis of this man’s condition?
**Core Concept**
The man's symptoms, combined with his history of raising chickens and a recent outbreak of a disease in his flock, suggest a zoonotic infection, specifically a disease caused by a pathogen that can be transmitted from animals to humans. In this case, the likely pathogen is a bacterium that causes a type of atypical pneumonia.
**Why the Correct Answer is Right**
The most likely diagnosis is **Avian Chlamydophila psittaci** infection, also known as Psittacosis. This bacterium is typically found in birds, including chickens, and can be transmitted to humans through inhalation of dust or dander contaminated with the bacteria. The symptoms of Psittacosis, such as chills, fever, and headache, are consistent with the man's presentation. The incubation period of Psittacosis is approximately 5-14 days, which matches the timeline of the man's exposure to the disease in his chicken flock.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a zoonotic pathogen, and the symptoms do not match those of a typical bacterial or viral pneumonia. **Option B:** This option is incorrect because Legionnaires' disease is a type of atypical pneumonia caused by Legionella bacteria, which is typically acquired through inhalation of contaminated water droplets, not through contact with animals. **Option C:** This option is incorrect because Histoplasmosis is a fungal infection caused by inhaling spores of the fungus Histoplasma capsulatum, which is typically found in bird and bat droppings.
**Clinical Pearl / High-Yield Fact**
When evaluating a patient with atypical pneumonia, it is essential to consider zoonotic pathogens, particularly if the patient has a history of exposure to animals or has recently handled animals. This is a classic exam trap, as many students may default to more common causes of atypical pneumonia without considering the broader differential diagnosis.
**Correct Answer:** C.