Susceptibility to vivax malaria in Ethiopia.

Plasmodium vivax prevalence rates for Nilotic and Hamitic-Semitic residents of an Ethiopian town were compared. Over a ten-year period, 8,316 blood films from Nilotes were examined and 59 P. vivax infections (0.7%) were diagnosed. In 1,630 films from Hamito-Semites, 75 probable P. vivax infections (4.6%) were found. The problem of morphological differentiation between P. vivax and P. ovale was evaded by combining the two diagnoses. P. vivax/ovale infection rates for Hamitic-Semitic subjects were higher than for Nilotic subjects in all age groups. It was concluded that the two populations are inately different in susceptibility to patient infection with vivax malaria.