Plasmodium falciparum merozoite surface protein 1 block 2 gene polymorphism in field isolates along the slope of mount Cameroon: a cross - sectional study

Abstract

Background: Malaria remains a major global health burden despite the intensification of control efforts, due partly to the lack of an effective vaccine. Information on genetic diversity in natural parasite populations constitutes a major impediment to vaccine development efforts and is limited in some endemic settings. The present study characterized diversity by investigating msp1 block 2 polymorphisms and the relationship between the allele families with ethnodemographic indices and clinical phenotype.

Method: Individuals with asymptomatic parasitaemia (AP) or uncomplicated malaria (UM) were enrolled from rural, semi-rural and semi-urban localities at varying altitudes along the slope of mount Cameroon. P. falciparum malaria parasitaemic blood screened by light microscopy was depleted of leucocytes using CF11 cellulose columns and the parasite DNA genotyped by nested PCR.

Results: Length polymorphism was assessed in 151 field isolates revealing 64 (5) and 274 (22) distinct recombinant and major msp1 allelic fragments (genotypes) respectively. All family specific allelic types (K1, MAD20 and RO33) as well as MR were observed in the different locations, with K1 being most abundant. Eighty seven (60 %) of individuals harbored more than one parasite clone, with a significant proportion (p = 0.009) in rural compared to other settings. AP individuals had higher (p = 0.007) K1 allele frequencies but lower (p = 0.003) mean multiplicity of genotypes per infection (2.00 ± 0.98 vs. 2.56 ± 1.17) compared to UM patients.

Conclusions: These results indicate enormous diversity of P. falciparum in the area and suggests that allele specificity and complexity may be relevant for the progression to symptomatic disease.

Fig. 1

Map of the study area. Localities on the slope of Mt. Cameroon included in the survey are indicated by blue triangles

Fig. 2

Banding pattern of msp1 block 2 alleles in asymptomatic and symptomatic P. falciparum infections along the slope of mount Cameroon. A = K1, B = MAD20; C = RO33; D = MR; M = 1 kb plus molecular weight marker; 1 – 11 = selected samples; N = negative control

Fig. 3

Fragment size polymorphisms (A1 and A2) and allele frequencies (B1 and B2) of msp1 block 2 allele families in participants with uncomplicated malaria (UM) and asymptomatic parasitaemia (AP) respectively