Dynamics of Plasmodium falciparum alleles in children with normal haemoglobin and with sickle cell trait in western Uganda

Abstract number: 1732_42

Kiwanuka G., Joshi H., Isharaza W., Eschrich K.

This is the first study to characterise Plasmodium falciparum population in relation to haemoglobin type in western Uganda.

General objective: To investigate the composition of P. falciparum in children aged 3 months to 15 years in Western Uganda and characterise the genotype of P. falciparum with the longest duration of carriage in sickle cell trait. Specific objectives: To study the allelic variants of P. falciparum in children aged 3 months to 15 years reporting at Mbarara University Teaching Hospital and Kagando Hospital, in western Uganda; to analyse the duration of carriage of specific parasite genotypes in relation to the type of haemoglobin of the children; to characterise P. falciparum harboured by asymptomatic malaria carriers with sickle cell trait; to investigate the effect of turnover of P. falciparum genotypes on parasite density.

Methods: Microscopic identification of malaria parasites and estimation of parasitaemia was done using Giemsa-stained thick and thin blood films. Haemoglobin phenotype was determined by electrophoresis of blood samples on cellulose acetate membrane in alkaline buffer. Nested PCR using specific primers for merozoite surface protein (MSP) 1 and 2 allelic families was used to genotype P. falciparum in 291 isolates collected from children in two districts Mbarara and Kasese.

Results: Extensive genetic diversity was detected among symptomatic children in Mbarara (20 MSP1; 31 MSP2 alleles) and Kasese (19 MSP1; 30 MSP2 alleles). Multiplicity of infection (MOI) with MSP2, a high polymorphic genetic marker, was higher in Kagando than in Mbarara being 2.1 and 2.7 genotypes/PCR positive-sample, respectively. The difference in MOI in children in the two districts was statistically significant (MSP1 P < 0.0001; MSP2 P = 0.036). Clear differences in the distribution of individual alleles of FC27, IC and RO33 were apparent in the study areas. A deletion of a 12-amino acid sequence in RO33 160 bp allele yielded RO33 130 bp, which predominated in symptomatic children in Mbarara. About 13% of asymptomatic children in Kisinga, Kasese carried HbAS. MOI was age-dependent and higher in children with HbAS than with HbAA. Haemoglobin type influenced the distribution of FC27-type alleles among asymptomatic children Kagando.

Conclusion:P. falciparum polymorphism is extensive in western Uganda, and most of the infections are composed of multi-clonal infections. HbAS increases MOI and is important in development of naturally acquired immunity.