A case-control study in northern Liberia of Plasmodium falciparum malaria in haemoglobin S and β-thalassaemia traits

Abstract

A case-control study was carried out on 558 patients with malaria attending a hospital in Yekepa, northern Liberia; 94 patients (16–8%) were aged at least ten years, probably because of a low level of protective immunity in town dwellers due to malaria control. The proportion of sickle cell traits (1·8%) among the patient group was lower than in the population (7·2%) served by the hospital (χ², 21·455, 1 df P<0·001). A stratified analysis showed the relative risk for Plasmodium falciparum malaria in sickle cell trait over normal homozygotes, as 0·29 (upper 95%) confidence interval, 0·56). For β-thalassaemia trait, the proportion among patients was 5·5% as against 9·0% in the general population (χ², 6·158, 1 df 0·025>P>0·010). Stratified analysis gave a weighted relative risk for β-thalassaemia heterozygotes of 0·49 (upper 95% confidence interval, 0·74). Although there were four β-thalassaemia traits in the 10–14 year stratum with moderate to high parasitaemias, we consider that the overall results are consistent with relative resistance against P. falciparum malaria of both sickle cell and β-thalassaemia heterozygotes in this population. No conclusions were possible from this investigation with regard to HbC and the malaria hypothesis. We found no evidence that P. falciparum malaria elevates HbA₂ concentrations into the β-thalassaemia range.