Chronic Pneumonias and Fungal Infections

Chronic Pneumonias

• Chronic pneumonia is often synonymous with 4 classic fungal or granulomatous pulmonary infections.
• If you see pulmonary granulomas, think of a chronic process that often takes years.

Histoplasmosis, Coccidiodomycosis, Blastomycosis

• These infections are caused by dimorphic fungi and can occur in normal hosts or those who are immunocompromised.
• Epidemiology: geographic distribution is key, with Histoplasma found in the Ohio and central Mississippi River valleys, Coccidiodomycosis found in the SW and far western regions of the US, and Blastomycosis found in areas that overlap with those in which Histoplasmosis is found.
• Morphology:
  • Histoplasma: round to oval, small yeast forms (2-5 µm in diameter)
  • Coccidiodomycosis: thick-walled, nonbudding spherules (20-60 µm), often filled with small endospores
  • Blastomycosis: round to oval yeast forms (5-25 µm) that reproduce by characteristic broad-based budding
• Presentation and pathology are very similar to TB, with acute primary pulmonary infection, chronic cavitary pulmonary infection, disseminated miliary infection, and identification of yeast forms (silver stains).
• Clinical symptoms resemble those of a "flulike" illness, and can be self-limited, but may develop into disseminated disease in infants or immunocompromised adults.

Infections in Immunocompromised Patients

• CMV Mononucleosis:
  • In healthy individuals, often asymptomatic, with most patients recovering without sequelae
  • In immunocompromised patients, can cause necrotizing interstitial pneumonia, retinitis, and GI ulcerations
  • Common in AIDS patients and transplant recipients
• Pneumocystis carinii:
  • Previously classified as a protozoon, now considered a fungus
  • Opportunistic infection in AIDS, often with CMV reactivation
  • Diagnosis: stains, PCR, and identification of organisms in induced sputum or bronchoalveolar lavage fluid
  • Clinical picture: fever, dry cough, dyspnea, hypoxia, and bilateral perihilar and basilar nodular infiltrates on chest X-ray
• Opportunistic Fungal Infections:
  • Candidiasis:
    • Most common disease-causing fungus
    • Pseudohyphae are an important diagnostic clue
    • Clinical features: involve the mouth, skin, and deep organs, with thrush, esophagitis, vaginitis, and skin infections
  • Cryptococcosis:
    • Opportunistic infection, especially in AIDS or hematolymphoid malignancies
    • Thick, gelatinous capsule and reproduces by budding
    • Clinical features: range from florid proliferation to granulomatous reaction
  • Aspergillosis:
    • Hyphae are septate
    • Invasive pulmonary aspergillosis: multifocal necrotizing pneumonia, may invade blood vessels, and disseminate with vasculitis, occlusion, and infarction
    • Aspergilloma: growing in existing cavities, especially in TB and bronchiectasis
  • Mucormycosis:
    • Caused by Zygomycetes (Rhizopus and Mucor)
    • Hyphae are nonseptate and branch at right angles
    • Clinical features: patients with DKA develop fulminant invasive rhinocerebral mucormycosis, and may also affect the lungs, with localized cavity or miliary disease

Tuberculosis

• WHO: the most common cause of death resulting from a single infectious agent
• TB is an ancient infectious disease caused by Mycobacterium tuberculosis (MTB)
• Infects one third of the world population, with 8-10 million new cases and 1.5 million deaths per year
• Underprivileged populations are most affected, with poverty, overcrowding, poor personal and public hygiene, and poor nutrition contributing to transmission
• Optimal conditions for transmission include poverty, overcrowding, and poor nutrition
• Both progressive 1º and 2º TB can result in systemic seeding, causing life-threatening forms of disease, such as miliary tuberculosis and tuberculous meningitis