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.
The prevalence of typhoid in the Papua New Guinea (PNG) highlands region increased rapidly in the mid-1980s, and now remains endemic. In this study ribotyping has been used to examine the number and types of Salmonella enterica serovar Typhi strains present during the 1977-1996 period. The ribotyping banding pattern results were based on Cla I and Eco RV digests. The 57 PNG isolates were divided into 11 different ribotypes. Comparison of ribotypes using coefficient of similarity values revealed a diverse group of ribotypes. Several strains appear to be endemic in PNG For instance, ribotypes 1, 2 and 3 were most commonly found among PNG isolates and isolates with these ribotypes have been cultured over a period of at least 11 years (1985-1996). Ribotype 3 was also observed in isolates from Malaysia and Thailand. Also found in PNG were ribotypes 4, 5, 6, 7, 8, 9, 16 and 17. The ribotyping suggests that serovar Typhi strains present in PNG include unique strains of serovar Typhi and also strains that are common to other countries.