classical histoplasmosis

What are the synonyms of histoplasmosis?

Small form histoplasmosis, Darling's disease, reticuloendothelial cytomycosis.

What organism causes histoplasmosis?

Histoplasma capsulatum var. capsulatum.

What is the teleomorph of Histoplasma capsulatum var. capsulatum?

Ajellomyces capsulatus.

What type of parasite is Histoplasma capsulatum in host tissue?

Facultative intracellular parasite of macrophages.

What kind of structure connects the daughter and mother yeast cells of Histoplasma capsulatum?

A narrow attachment point.

What unique morphological feature surrounds the yeast cells in tissue?

A clear halo around darker-staining central material.

Which animals are important vectors of histoplasmosis?

Birds (black birds, sea gulls, starlings, pigeons) and bats.

Where in the environment is Histoplasma capsulatum commonly isolated from?

Soil in bat caves, bird roosts, chicken houses, and pigeon-inhabited silos.

Which agar is used to culture Histoplasma capsulatum at 25°C?

Sabouraud agar with chloramphenicol but without cycloheximide.

Which agar is used to culture the yeast phase at 37°C?

Brain heart infusion agar with blood or blood agar.

What forms of conidia are seen in the mycelial phase of H. capsulatum at 25°C?

Small, round microconidia and large thick-walled macroconidia with knob-like projections.

What is the primary mode of infection for histoplasmosis?

Inhalation of spores of the dimorphic fungus.

Can histoplasmosis be transmitted from animal to animal?

No, Histoplasma capsulatum is not contagious.

What clinical form does histoplasmosis most commonly take?

Pulmonary form.

Which domestic species is particularly susceptible to histoplasmosis?

Dogs.

Which laboratory animal is highly susceptible to histoplasmosis?

Mice.

What kind of lesions are typically seen in the lungs of infected animals?

Epithelioid and giant cell granulomas.

Which organ systems may histoplasmosis invade beyond the lungs?

Adrenal glands, bone marrow, gastrointestinal tract, liver, lymph nodes, spleen.

What may help disseminate histoplasma in the host?

Macrophages carrying the organisms to different body sites.

What determines the clinical form of histoplasmosis in the host?

Host immunity and the number of spores inhaled.

What are some severe signs of disseminated histoplasmosis?

Hepatomegaly, splenomegaly, anemia, leucopenia.

What is a characteristic symptom of chronic pulmonary histoplasmosis?

Cavities in the apex or subapical regions of the lungs.

What is a notable histological feature in stained tissue sections of histoplasmosis?

Organisms within macrophages with a clear halo.

Why is the skin test not reliable for detecting active histoplasmosis?

It remains positive for life and may interfere with serological tests.

Which test is considered confirmatory for histoplasmosis?

Complement fixation test.

Which tests are useful for screening histoplasmosis?

Latex agglutination test and fluorescent antibody test.

Which test may show two bands indicating active or past infection?

Immunodiffusion test.

What is the primary drug of choice for treating histoplasmosis?

Amphotericin B.

Which other drugs may be effective against histoplasmosis?

Ketoconazole, sulfonamides, ethylvallinate.

How long after infection do antibody titers from complement fixation fall off?

Gradually and disappear by nine months.

What complicates serological testing in histoplasmosis?

Cross-reactivity with antigens of other systemic fungal pathogens.

What are some common clinical signs in symptomatic pulmonary histoplasmosis?

Fever, night sweats, weight loss, hemoptysis.

What may happen to lesions over time in histoplasmosis?

Lesions tend to become calcified.

Which parts of the world are most commonly affected by histoplasmosis?

America, parts of Africa and Asia.

In the United States, where is histoplasmosis most prevalent?

Midwest and much of the eastern half.

What is a clinical feature of histoplasmosis affecting the tongue and eyes?

Nodules on the tongue and ocular involvement.

Can histoplasmosis cause reproductive issues?

Yes, abortion has been reported.

What is the appearance of the yeast cells in tissue under the microscope?

Small oval yeast cells with or without buds and a surrounding clear halo.

What types of specimens may be used to detect Histoplasma in diagnosis?

CSF, biopsies, bone marrow, lymph nodes, or buffy coat.

What histological stains are used to visualize Histoplasma in tissue?

Gomori methenamine silver or Periodic acid-Schiff (PAS) stains.

Where are the yeast cells of Histoplasma capsulatum usually located in tissue?

Within macrophages.

Why is complement fixation preferred over skin testing for diagnosis?

Skin testing interferes with serology and doesn't indicate active disease.

What is a limitation of the complement fixation test in histoplasmosis?

Cross-reactivity with other systemic fungal pathogens.