Histoplasmosis

Histoplasmosis is an inhalational fungal infection acquired when soil or organic material contaminated with bird or bat droppings is disturbed. The clinical question is not simply whether exposure occurred. It is whether the patient can contain the yeast after inhalation: intact T-cell immunity usually limits disease to an asymptomatic or self-limited pulmonary illness, while advanced HIV, transplantation, TNF inhibition, or other impaired cellular immunity can permit dissemination to the marrow, liver, spleen, adrenal glands, and central nervous system. For a Canadian NP, the useful starting point is an exposure-and-immunity assessment. Ask what material was aerosolized, when the exposure occurred, and whether the patient has a condition or medication that weakens cellular immunity. Then match the illness pattern to the likely phenotype, choose tests with appropriate sensitivity and timing, and treat according to severity, site, pregnancy status, and drug-safety constraints.