The colonies seen growing on the blood agar in the upper image on the right are gray-white and have a delicate cob-web appearance. The lactophenol blue mount (lower image) reveals delicate background hyphae (thus the cob-web appearance of the colonies) and the production of macroconidia with a conspicuous prickly surface, characteristic of Histoplasma capsulatum.
Histoplasmosis is a systemic disease, mostly of the reticuloendothelial system. It may manifest itself in the bone marrow, lungs, liver, and/or spleen. The primary indication of infection in children is hepatosplenomegaly. In adults, it most often occurs as pulmonary disease.
Histoplasmosis can be transmitted through the guano of bats and birds, particularly chickens and blackbirds. It could be contracted by individuals who frequent caves in endemic areas such as Kentucky and other states in the lower Missouri and Mississippi river valleys or who are in contact with soil containing bird guano.
Specimens sent to the laboratory may include bronchial alveolar lavage (BAL), if it is pulmonary disease, or biopsy material from the diseased organ. H. capsulatum may be observed in bone marrow or even intracellularly in white blood cells in peripheral blood (usually monocytes or neutrophils).