Trends in multiplicity of Plasmodium falciparum infections among asymptomatic residents in the middle belt of Ghana

Akua Agyeman-Budu,Michael Wilson,Mohammed Adams,Brian Greenwood,Seth Owusu-Agyei,Dominic Dery,David Dosoo,Charles Brown,Kwaku P Asante,George Adjei

doi:10.1186/1475-2875-12-22

Abstract

BackgroundMalaria is the most important cause of mortality and morbidity in children living in the Kintampo districts in the middle part of Ghana. This study has investigated the multiplicity of infection (MOI) within asymptomatic residents of the Kintampo districts, and the influence of age and seasonality on MOI, by studying the distribution of the polymorphic Plasmodium falciparum antigen merozoite surface protein 2 (MSP2).MethodsDNA was extracted from an asymptomatic cohort of children and adults infected with P. falciparum during the period November 2003 to October 2004. Polymerase chain reaction was carried out and multiplicity of infection (MOI) was determined.ResultsChildren under 10 years of age had an average MOI of 2.3 while adults 18 years and above had an average MOI of 1.4. Children below five years had high and low average MOIs of 2.8 in the March/April survey and 0.9 in the May/June survey respectively. A similar trend in the monthly distribution of MOI was observed for the entire cohort. IC/3D7 strains outnumbered the FC27 strains throughout the year by a ratio of about 4:1 with the difference between the prevalence of the two strains being least marked in the March/April survey, at the beginning of the rainy season. MOI was not linked to the level of malaria transmission as measured by the entomological inoculation rate.Discussion/conclusionThe impact of interventions, introduced since this baseline study was carried out on the parasite diversity of asymptomatic residents will be the subject of further investigations.

Highlights

Malaria is the most important cause of mortality and morbidity in children living in the Kintampo districts in the middle part of Ghana
This study examined the distribution of multiplicity of infection (MOI) and parasite densities in children less than five years, during different months of the study year as well as the relationships between monthly malaria transmission and merozoite surface protein 2 (MSP2) allelic variants
The only obvious reason which may have led to the lower polymerase chain reaction (PCR) success rate in the sixth round can be attributed to the quality of samples received for analyses

Summary

Introduction

The recent reports from Kintampo have shown decreasing parasite densities with increasing age [5,6], amidst entomological inoculation rates (EIR) of 231–269 infective bites per person per year (ib/p/y) [7]. In these reports, EIR, which estimates the level of exposure of an individual to malaria-infected mosquitoes, was used to estimate the malaria transmission rate. In other malaria endemic areas, molecular studies have shown that the number of clones of malaria parasites co-infecting a single host is a useful indicator of transmission intensity, as well as a guide in determining the immune status of the host [8,9]. In holoendemic malarious areas high MOIs have not been related to clinical malaria among older children, [11,12,13] while in areas of lower transmission, positive relationships between high MOIs and clinical malaria have been observed [14,15,16]

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Conclusion