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Blood smears from 13 patients infected with Babesia microti were reviewed to define the range of morphologic characteristics of the organism. Organisms resembling rings of Plasmodium falciparum were the predominant forms in all patients' blood smears. Babesia microti and Plasmodium spp. may be differentiated by the presence of pigment deposits in erythrocytes parasitized with mature stages of Plasmodium.

Parasitologic, serologic, and epidemiologic studies were done during 1967 in Calion, Arkansas (population 544). Infection with Entamoeba histolytica was found to be endemic but was segregated along racial lines. Twenty-two (9.9%) black compared with only one (0.6%) white had E. histolytica demonstrated in one stool examination; only two blacks had symptoms suggestive of amebiasis. No positive amebiasis indirect hemaggulination titers were found in 135 white residents. In contrast, 41 (17.9%) blacks had positive titers. Age, sex, and geographic location were not associated with stool or seropositivity. Within the black population, clustering of stool and seropositivity occurred. Significantly higher rates of stool and seropositivity were seen in households with crowding and poor sanitation as evidenced by lack of indoor toilet facilities. The presence of contaminated water supplies did not correlate with stool or seropositivity. The probable importance of person-to-person transmission is suggested by the observed clustering of infection within households with crowding and unsanitary conditions. The absence of evidence for transmission by food or water further supports this hypothesis.