The resistance factor to Plasmodium vivax in blacks.

The authors showed that the Plasmodium vivax parasite requires the Fya/Fyb Duffy antigen/chemokine receptor on the surface of red blood cells for penetration of human red blood cells. Because most African and American blacks have the FyFy genotype they are resistant to infection by P. vivax.

(Thanks to Juan Weiss for this reference and its interpretation.)