Which option best summarizes the pathogenic behavior of C. burnetii after inhalation?

Which option best summarizes the pathogenic behavior of C. burnetii after inhalation?

• A. It is killed rapidly by neutrophils
• B. It replicates only outside host cells
• C. It causes disease only in humans
• D. It survives intracellularly within host cells such as monocytes

Answer: (D)

Intracellular survival inside monocytes/macrophages is the hallmark of how this organism behaves after inhalation. Coxiella burnetii is an obligate intracellular bacterium, meaning it must live and replicate within host cells. After being inhaled, it is taken up by alveolar macrophages and then persists inside the phagolysosome, where the acidic environment actually supports its replication rather than killing it. This intracellular niche protects it from extracellular immune defenses and allows it to disseminate via the bloodstream to organs like the liver and spleen. It’s not quickly destroyed by neutrophils, and it does not replicate outside cells, and its disease isn’t limited to humans, so the best description of its pathogenic behavior after inhalation is that it survives intracellularly within host cells such as monocytes.

Intracellular survival inside monocytes/macrophages is the hallmark of how this organism behaves after inhalation. Coxiella burnetii is an obligate intracellular bacterium, meaning it must live and replicate within host cells. After being inhaled, it is taken up by alveolar macrophages and then persists inside the phagolysosome, where the acidic environment actually supports its replication rather than killing it. This intracellular niche protects it from extracellular immune defenses and allows it to disseminate via the bloodstream to organs like the liver and spleen. It’s not quickly destroyed by neutrophils, and it does not replicate outside cells, and its disease isn’t limited to humans, so the best description of its pathogenic behavior after inhalation is that it survives intracellularly within host cells such as monocytes.