Allelic diversity of merozoite surface protein 2 gene of P falciparum among children in Osogbo, Nigeria

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Abstract

The genetic diversity of Plasmodium falciparum (P falciparum) infections in humans is implicated in the pathogenesis of malaria. This study provides the first estimate of the genetic diversity and genotype multiplicity of Plasmodium falciparum infection in children with uncomplicated P falciparum malaria in Osogbo, Nigeria. One hundred and one isolates were used for analysis of parasite population polymorphism and genotyped by nested-PCR of merozoite surface protein 2 (MSP2) block 3. Amplicons were obtained for all the 101 genotyped samples in MSP2 PCR with 9 alleles varying in size between 300 and 800 base pair. Thirty-three (31.7%) samples had FC27 allele while 27 (26.7%) had 3D7 allele and 35 (34.7%) had mixed alleles (3D7+FC27). The Multiplicity of Infection (MOI) in the population was 1.6. Children in the age group of > 4-8 years had the highest number of different genotypes in their samples (1.8). The number of MSP2 bands per isolate was lower in the older age group (1.3) but the difference was not statistically significant. Children with parasite density range 5001-10 000 had the highest MOI of 2 while those with parasite density range 1000-5000 had the lowest of1.5. In conclusion, the present study shows that the field isolates are highly diverse in respect ofMSP2 and multiplicity of infection was neither age nor parasite density dependent in the study population.

Translated abstract

La diversidad genética de las infecciones por Plasmodium falciparum en los humanos se halla implícita en la patogénesis de la malaria. Este estudio proporciona un primer estimado de la diversidad genética y multiplicidad del genotipo de la infección por Plasmodium falciparum en los niños con malaria por P falciparum malaria sin complicaciones en Osogbo, Nigeria. Ciento un aislados fueron usados para el análisis del polimorfismo de la población parasitaria, y genotipificados mediante reacción en cadena de la polimerasa (RCP) anidada de la proteína de superficie del merozoíto 2 (MSP2) bloque 3. Se obtuvieron amplicones para las 101 muestras genotipificadas con RCP de MSP2, con 9 alelos variando en tamaño entre 300 y 800 par de bases. Treinta y tres (31.7%) muestras tenían el alelo FC27 mientras 27 (26.7%) tenían el alelo 3D7 y 35 (34.7%) tenían alelos mezclado (3D7+FC27). La multiplicidad de infección (MOI) en la población fue 1.6. Los niños en el grupo etario de > 4-8 años tenían el número más alto de genotipos diferentes en sus muestras (1.8). El número de bandas de MSP2 por aislado era más bajo en el grupo etario de mayor edad (1.3) pero la diferencia no era estadísticamente significativa. Los niños con un rango de densidad parasitaria 5001-10 000 tenían el MOI más alto equivalente a 2, mientras aquéllos con rango de densidad parasitaria 1000-5000 tenían el MOI más bajo equivalente a 1.5. En conclusión, el presente estudio muestra que los aislados de campo son altamente diversos con respecto al MSP2, y que la multiplicidad de la infección no depende ni de la edad ni de la densidad parasitaria de la población en estudio.

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Daily dynamics of Plasmodium falciparum subpopulations in asymptomatic children in a holoendemic area.

I Rooth, Anders Björkman, G Snounou … (1997)

Plasmodium falciparum is the major cause of malaria morbidity and mortality in the world. Biologic and antigenic diversity is a characteristic of this parasite and infections can consist of several genetically diverse parasites. The daily dynamics of these parasite subpopulations were investigated in asymptomatic children in rural Tanzania. Fingerprick blood samples were collected on 14 consecutive days from 20 children. Parasite densities were detected by light microscopy and genotyping of P. falciparum was done using a nested polymerase chain reaction (PCR) assay targeting polymorphic regions on the merozoite surface protein-1 (MSP-1), MSP-2, and glutamine-rich protein (GLURP) genes. In the eight children harboring P. falciparum throughout the study period, infections were found to be highly complex with daily changes in both parasite density and genotypic pattern. A nonrandom. 48-hr periodicity in these fluctuations suggests that P. falciparum infections consist of inherently synchronous subpopulations of parasites. These findings have important biologic and epidemiologic implications since one blood sample may only partly reflect the whole parasite population in an infected individual.

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No influence of age on infection complexity and allelic distribution in Plasmodium falciparum infections in Ndiop, a Senegalese village with seasonal, mesoendemic malaria.

J Trape, G Snounou, D. Fontenille … (1998)

We have shown previously that in Dielmo, a Senegalese village with intense perennial Plasmodium falciparum transmission, the infection complexity and the distribution of some allelic types harbored by asymptomatic carriers was age-dependent. We report here an investigation of these parameters in Ndiop, a village located 5 km from Dielmo, where malaria is mesoendemic and seasonal, and where immunity is acquired at a very low rate, as indicated by the lifelong distribution of P. falciparum clinical attacks. Blood was collected from 143 and 125 inhabitants, including 122 individuals sampled in both surveys, during two cross-sectional surveys at one-month intervals during the 1994 transmission season. Plasmodium falciparum parasites were genotyped for three polymorphic single copy genes. Genetic diversity was very large, with 17, 43, and nine distinct alleles detected for the merozoite surface protein-1 (MSP-1), MSP-2, and glutamate-rich protein loci, respectively. These figures, similar to those previously observed in Dielmo, indicate that the parasite genetic diversity is not directly related to the inoculation rate, at least in the range of transmission intensity studied here. The complexity of the asymptomatic infections (average number of distinct genotypes per isolate) was more than two-fold lower in Ndiop than in Dielmo and importantly, did not decrease with age. Likewise, the allele distribution was not influenced by age, contrasting with the observations made in Dielmo. This indicates that the number of parasite types per isolate and the influence of age on complexity and allele distribution depend on the level of endemicity, consistent with the interpretation that they reflect acquired anti-parasite immunity.