Hereditary ovalocytosis and reduced susceptibility to malaria in Papua New Guinea

Abstract

Ovalocytosis, an hereditary condition in which most erythrocytes are oval in shape, is a polymorphism that occurs in up to 20% or more of the population in Papua New Guinea and Malaysia. Due to the geographical correlation of the trait with endemic malaria, the possibility of a selective advantage in resistance to malaria has been raised. In a study of 202 individuals with greater than or equal to 50% oval red cells matched by age, sex and village of residence with controls having less than or equal to 30% oval cells, ovalocytic subjects had blood films negative for Plasmodium vivax (P = 0.009), for P. falciparum (P = 0.044), and for all species of malaria parasites (P = 0.013), more often than controls. Among individuals parasitaemic at any time there were no clear differences in density of parasitaemia. However, in children 2 to 4 years old, parasite densities of both species were lower in ovalocytic subjects than in controls (0.01 less than P less than 0.025). The differential susceptibility to malaria infection suggested by this study has implications for the evaluation of interventions, including possible future vaccine field trials, in populations where high-frequency ovalocytosis is present.

Population genetics of malaria resistance in humans

“…For example, the frequency of the deletion was 0.146 in a sample of healthy Papua New Guinea children whereas it was not present in any of the children with cerebral malaria (Genton et al, 1995 see also;Allen et al, 1999). Carriers also appear to be at lower risk of infection by both P. vivax and P. falciparum (Cattani et al, 1987; however, see Kimura et al, 2002).…”

Evolutionary and Historical Aspects of the Burden of Malaria

“…Ovalocytosis occurs at high frequencies (up to 20%) in the highly malarious lowlands of New Guinea but virtually disappears in the malaria-free highlands. Carriers of the trait are at reduced risk of infection with P. falciparum and, especially, P. vivax malaria (26).…”

Ability of Plasmodium falciparum to invade Southeast Asian ovalocytes varies between parasite lines

“…On the other hand, SAO individuals are fully susceptible to severe malaria anemia and clinical uncomplicated malaria. 18 Although early studies, conducted before the presence of the SAO trait could be determined unambiguously by polymerase chain reaction (PCR), suggested that SAO individuals exhibit some degree of protection against prevalence of malaria parasites or against high-density P falciparum infections, [20][21][22] later studies demonstrated that SAO individuals suffer high-density infections by P falciparum and this trait only has minor effects, if any, on the prevalence and density of P falciparum infections. 18,23 Our recent finding that SAO infected RBCs (IRBCs) have altered adherence properties compared with normal IRBCs (A.C., M. Mellombo, C.S.…”