Intraerythrocytic parasitosis in humans with Entopolypoides species (family Babesiidae). Association with hepatic dysfunction and serum factors inhibiting lymphocyte response to phytohemagglutinin.

We have observed two cases of human infection with intraerythrocytic protozoa. The organisms appeared to be in the Entopolypoides group, which had not previously been associated with human infection. One patient was asplenic. Both patients had hepatic dysfunction, and their serum samples contained blocking factors that interfered in vitro with the stimulation of normal lymphocytes by phytohemagglutinin. It appears that in humans, as well as in experimental animals, host factors are important in resistance to infection by intraerythrocytic parasites. These factors include the presence of a spleen and cell-mediated and humoral immunities. Possibly similar infections will be observed in patients with other impairments of T-cell function, such as those induced by malignancy, thymic dysfunction, or immunosuppressive drugs.