RS13 - Respiratory Fungal Infections

What organism causes histoplasmosis?

Histoplasma capsulatum.

What type of fungus is Histoplasma capsulatum?

Dimorphic: mold at room temperature and budding yeast at 37°C.

Where is Histoplasma capsulatum most prevalent in the US?

Midwest and southeastern US (Ohio and Mississippi River valleys).

What environment is Histoplasma associated with?

Soil with high nitrogen content associated with bird and bat droppings.

How is histoplasmosis acquired?

Inhalation of mycelial fragments and microconidia from soil.

What percentage of Histoplasma infections are symptomatic?

Approximately 5% result in symptomatic disease.

How does Histoplasma survive in the host?

Grows within unactivated macrophages.

What immune response controls Histoplasma infection?

Effective T cell-mediated immunity.

What happens if host defenses are impaired in histoplasmosis?

Progressive, potentially fatal pulmonary or disseminated disease.

How is acute pulmonary histoplasmosis treated if not improving after 1 month?

Itraconazole for 6-12 weeks.

What is used to treat disseminated histoplasmosis?

Amphotericin B.

What is presumed ocular histoplasmosis syndrome (POHS)?

Atrophic chorioretinal scars, peripapillary atrophy, absence of vitritis caused by hematogenous spread of H. capsulatum.

What organism causes coccidioidomycosis (Valley Fever)?

Coccidioides immitis.

Where is coccidioidomycosis endemic in the US?

Southwestern US (Southern California, Nevada, Arizona, New Mexico, Texas).

How is coccidioidomycosis transmitted?

Inhalation of spores from soil.

What percentage of coccidioidomycosis infections are asymptomatic?

50-66%.

What complication can develop from coccidioidomycosis pulmonary infection?

Pulmonary cavitation and chronic fibrotic pneumonic process.

Who is most at risk for extrapulmonary dissemination of coccidioidomycosis?

Immunocompromised patients.

What organism causes Pneumocystis pneumonia (PCP)?

Pneumocystis jirovecii.

Who is most susceptible to Pneumocystis pneumonia?

Patients with HIV/AIDS and low CD4 counts.

How is Pneumocystis pneumonia treated?

Trimethoprim-sulfamethoxazole (Bactrim, co-trimoxazole).

Why are typical antifungals not effective for Pneumocystis jirovecii?

Fungus differs in its cell wall and membrane and is not responsive to usual antifungal drugs like fluconazole or itraconazole.

What organism causes aspergillosis?

Aspergillus species (A. fumigatus most common).

Who is most susceptible to invasive aspergillosis?

Severely immunocompromised or neutropenic patients.

What are the forms of aspergillosis?

Allergic reactions, colonization ("fungal ball"), limited invasive infection, frankly invasive pulmonary infection.

Which form of aspergillosis is most severe?

Frankly invasive pulmonary infection.

What are symptoms of invasive aspergillosis?

Fever, pulmonary infiltrates, chest pain, coughing up blood.

What is the mortality rate of invasive aspergillosis?

Up to 70%.

How is aspergillosis treated?

Voriconazole (preferred) or amphotericin B.

Where does aspergillus typically colonize?

Obstructed paranasal sinuses, bronchi, preformed pulmonary cavities.

What is the most frequent respiratory fungal infection in AIDS patients?

Pneumocystis pneumonia.