Histoplasma capsulatum

• common in the Midwest

• associated with bird and bat droppings

• asymptomatic infection is the rule

Histoplasmosis typical case presentation

• 60-yo farmer decides to move a small chicken house

• several days later, develops fever, cough, SOB

• reticulonodular pulmonary infiltrate with a moderate-to-severe illness and a prolonged recovery

Appearance

• fluffy white mold in culture

• conidia show up as tubercles/spikes on the mycelia

• the actual infectious form is the microconidia

Histopathology

• silver stain: the fungi are dividing inside macrophages

• punctate appearance inside the macrophages

• PAS stain: narrow-neck budding of fungi

Geographical distribution

• most intensely endemic around the Ohio river valley—states include OH, TN, AK, IN

• however, you can get it anywhere in the South or in Texas

• you can get it even in CA, though this is very uncommon

Endemic in the Americas

• not as highly endemic in Central and South America, but still endemic

Clinical manifestations

• acute pulmonary

• chronic pulmonary

• disseminated

• fibrosing mediastinitis (very rare)

Disseminated disease

• occurs primarily in the immunocompromised

• most commonly, GI tract, miliary disease, spleen, liver, adrenal glands, CNS

Mucocutaneous dissemination

• tongue lesion

• ankle lesion

GI dissemination

• look like bowel cancers on X-ray

• upon scoping, trabeculated lesions

Disseminated histo

• immunosuppression is already present in 2/3 of those affected

  • steroids, 1970s

  • AIDS, 1980s

  • TNF inhibitors for Rx arthritis, 2000s

• FUO (fever of unknown origin)

• RE tissues

• focal lesions

Detection of circulating antigen in the urine

• second-generation antigen test is more predictive than the old one

• more true positives, fewer false negatives

Histology of a lung from a patient on Etanercept, a TNF inhibitor

• diffuse pulmonary infiltrate

• the infection is very common in the central and eastern US

Category: Microbiology Notes