Epidemiology

The distribution of histoplasmosis is quite different from that of coccidioidomycosis. Figure 23.27 shows the distribution of histoplasmosis in the United States, but the disease also occurs in tropical and temperate zones scattered around the world. Cave explorers, spelunkers, are at risk for contracting the disease because many caves contain soil enriched with bat droppings. Most cases of histoplasmosis in the United States have occurred in the Mississippi and Ohio River drainage area and in South Atlantic states. Skin tests reveal that millions of people living in these areas have been infected.

Table 23.14 Coccidioidomycosis

Symptoms

Incubation period Causative agent Pathogenesis

Epidemiology

Prevention and treatment

Fever, cough, chest pain, loss of appetite and weight; less frequently, painful nodules on extremities, pain in joints; skin, mucous membranes, brain, and internal organs sometimes involved

2 days to 3 weeks

Coccidioides immitis, a dimorphic fungus

After lodging in lung, arthrospores develop into spheres that mature and discharge endospores, each of which then develops into another sphere; inflammatory response damages tissue; hypersensitivity to fungal antigens causes painful nodules and joint pain

Inhalation of airborne C. immitis spores with dust from soil growing the organism. Occurs only in certain semi-arid regions of the Western Hemisphere

Dust control methods such as grass planting and watering.Treatment: amphotericin B and fluconazole

Macrophage nucleus Macrophage

Macrophage nucleus Macrophage

H. capsulatum

H. capsulatum

Figure 23.27 Geographic Distribution of Histoplasma capsulatum in the United States as Revealed by Positive Skin Tests Human histoplasmosis has been reported in more than 40 countries besides the United States, including Argentina, Italy, South Africa, and Thailand.

10 mm

Figure 23.27 Geographic Distribution of Histoplasma capsulatum in the United States as Revealed by Positive Skin Tests Human histoplasmosis has been reported in more than 40 countries besides the United States, including Argentina, Italy, South Africa, and Thailand.

10 mm

10 mm

Figure 23.26 Histoplasma capsulatum (a)Yeast-phase organisms packing the cytoplasm of a macrophage. (b) Mold phase, showing large conidia with projecting knobs.

10 mm

Figure 23.26 Histoplasma capsulatum (a)Yeast-phase organisms packing the cytoplasm of a macrophage. (b) Mold phase, showing large conidia with projecting knobs.

Table 23.15 Histoplasmosis

Symptoms

Mild respiratory symptoms; less frequently, fever, chest pain, cough, chronic sores

Incubation period

5 to 8 days

Causative agent

Histoplasma capsulatum, a dimorphic fungus

Pathogenesis

Spores inhaled, change to yeast phase, multiply in macrophages; granulomas form; disease spreads in individuals with AIDS or other immunodeficiencies

Epidemiology

The fungus prefers to grow in soil contaminated by bird or bat droppings, especially in Ohio and Mississippi River valleys, and in the U.S. Southeast. Spotty distribution in many other countries around the world. Spelunkers are at risk of infection

Prevention and treatment

Avoidance of soils contaminated with chicken, bird, or bat droppings.Treatment: amphotericin B and itraconazole for serious infections

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