Numerous yeast forms of Histoplasma capsulatum in alveolar macrophages. The rrowhead points to a halo formed when there is retraction of the cytoplasm.

The organism gains entry into the body via inhalation of dust particles containing spores from bird droppings. Immunosuppression is not a requirement for infection. The disease is endemic in the Ohio and Mississippi river valleys.

From the slide collection of the late Dr. Charles Kuhn