Fungal pneumonia pathophysiology

Fungi typically enter the lung with inhalation of their spores, though they can reach the lung through the bloodstream if other parts of the body are infected. Also, fungal pneumonia can be caused by reactivation of a latent infection. Once inside the alveoli, fungi travel into the spaces between the cells and also between adjacent alveoli through connecting pores. This invasion triggers the immune system to respond by sending white blood cells responsible for attacking microorganisms (neutrophils) to the lungs. The neutrophils engulf and kill the offending organisms but also release cytokines which result in a general activation of the immune system. This results in the fever, chills, and fatigue that is commonly seen in bacterial and fungal pneumonia. The neutrophils and fluid leaked from surrounding blood vessels fill the alveoli and result in impaired oxygen transportation.

Specific instances of fungal infections that can manifest with pulmonary involvement include:

• Pneumocystis jirovecii pneumonia
• Histoplasmosis, which has primary pulmonary lesions and hematogenous dissemination
• Coccidioidomycosis, which begins with an often self-limited respiratory infection (also called “Valley fever” or “San Joaquin fever”)
• Pulmonary blastomycosis
• Sporotrichosis – primarily a lymphocutaneous disease, but can involve the lungs as well
• Cryptococcosis – contracted through inhalation of soil contaminated with the yeast, it can manifest as a pulmonary infection and as a disseminated one
• Aspergillosis, resulting in invasive pulmonary aspergillosis
• Candidiasis – rarely has pulmonary manifestations in immunocompromised patients.

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