This stamp was part of the U.S. pledge to support the World Health Organization (WHO) in its campaign to eliminate malaria. Various human races have developed genetic defenses against malaria. African and Mediterranean peoples have genes for altered hemoglobin, on which the parasite that causes malaria thrive. People having one normal hemoglobin gene and one altered gene lessen their chances of acquiring malaria. Unfortunately, people who inherit two altered genes are subject either to sickle-cell disease or thalassemia.