Influences of Haemoglobin-As genotype on asymptomatic plasmodium infections in children in Nchelenge District,Luapula province, Zambia
Chianzu, Graham Pumulo
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Background: It is approximated that about 50% of malaria infections are asymptomatic in areas where malaria is endemic. In these areas, transmission is intense and consistent over time. As a result, most adults who live in these endemic areas possess partial immunity to malaria due to recurrent infections. Infants and children unfortunately, usually do not acquire this partial immunity early in life until they are exposed to malaria infection for a long time. These asymptomatic individuals continue transmitting the disease to others and provide a long-lasting reservoir for the malaria vector. It has been noted that there has been a higher prevalence of haemoglobin S in highly malaria endemic areas, especially in sub-Saharan Africa. And it has been reported that haemoglobin AS heterozygote [HbAS; sickle-cell trait] protects against severe disease & death due to Plasmodium falciparum. The aim of the study was to establish the effects of Sickle cell genotypes on asymptomatic malaria infection among children in Nchelenge district. Method: Malaria parasites were counted per 200 white blood cells [WBCs] on Giemsa-stained thick blood films, in determining parasitaemia & parasite density we calculated assuming a mean WBC count of 8000/μL. Malaria was defined as any parasitaemia plus fever. Samples from all participants with RDT positive, and blood smear negative and all positive blood smears [for parasite identification] were subjected to PCR. DNA was extracted from dried blood spots by Chelex DNA extraction, and submicroscopic infections were ascertained by nested PCR assays including commercial negative and positive controls. We extracted DNA using a QIAGEN kit and haemoglobin was typed by polymerase chain reaction-restriction fragment length polymorphism. Results: Microscopically visible parasitaemia was present in 35.9% (83) of the children, at overall geometric mean parasite density (4435.4/μL; 95%CI, 3292.5-5975.1/ μL). By PCR, P. falciparum occurred in 89% (104/116) while 11% (12/116) were other species of malaria. The HbAS trait was present in 24.4% (56/230) of the children, while 71.7% (165/230) had a normal haemoglobin genotype (HbAA). HbSS occurred in 3.9% (9/230) of the children. Children with HbAS had reduced parasite densities as compared to those with HbAA. Conclusion: In conclusion, our data showed that sickle cell trait (HbAS) protects against high parasitaemia, parasite density [P. falciparum] and anaemia in children, through the enhancement of the acquired and innate immunity, which inhibits parasite proliferation.