New emerging Plasmodium falciparum genotypes in children during the transition phase from asymptomatic parasitemia to malaria.

Abstract

Abstract. Semi-immunity against Plasmodium falciparum occurs after many infections. In areas of high malaria transmission, the prevalence of asymptomatic parasite carriers increases with age. We investigated P. falciparum genotypes in a cohort of asymptomatic carriers who were followed until they became symptomatic. Blood spots on filter paper and blood smears were collected daily from 10 children in Lambaréné, Gabon. The parasite genotypes present on successive days were determined by a polymerase chain reaction using the polymorphic region of the merozoite surface antigen-2 for typing. The same parasite genotypes persisted in eight out of ten children and parasite densities were low throughout the asymptomatic phase indicating inhibition of parasite growth. Appearance of symptoms was associated with an increase in parasitemia and appearance of novel parasite genotypes. The results suggest that the parasites causing a clinical episode are those against which a child has not yet mounted an efficient protective immune response.

No change in parasite genotype during single episodes of Plasmodium falciparum malaria in Gabonese children

“…Magesa and coworkers reported similar results, with daily changes in both parasite density and genotypic pattern (Magesa et al 2002). However, in another study by our group, we demonstrated the unchanging pattern of parasites over time during the asymptomatic phase of infection, with the appearance of a new genotype coinciding with clinical symptoms (Kun et al 2002). These studies (Fa¨rnert et al 1997;Magesa et al 2002;Kun et al 2002), which were investigating untreated infections, are fundamentally different from the present study, which follows patients undergoing quinine treatment.…”

“…The genetic composition of the parasites in an individual throughout the course of infection was not well known, because most studies were cross-sectional surveys of parasites in the blood of infected people at a single time-point. Nevertheless, longitudinal studies on asymptomatic children in eastern Africa showed a daily variation in the P. falciparum population (Fa¨rnert et al 1997) while, in Gabonese children, there was a constant parasite profile throughout an asymptomatic infection (Kun et al 2002). In patients with falciparum malaria, studies on the genetic characteristics of the parasite are so far limited to the association between parasite genotype and disease severity (Robert et al 1996;Kun et al 1998) or the association between the complexity of the infection and susceptibility to malaria (Fa¨rnert et al 1999).…”

The silent threat: asymptomatic parasitemia and malaria transmission

“…It has been suggested that reinfection with new clones (to which the individual had not previously been exposed) could trigger an increase in parasite density and the development of symptoms [56], but other studies have demonstrated that symptoms can appear without any change in clonal diversity [55].…”

High Prevalence of Gametocyte Carriage among Individuals with Asymptomatic Malaria: Implications for Sustaining Malaria Control and Elimination Efforts in Ethiopia

“…It was believed that longterm asymptomatic carriage may represent a form of tolerance to the parasite in adults as well as children, building up their immune response, thereby protecting them from developing either a mild malarial attack or a more severe one by keeping their immunity effective. 3 On the other hand, asymptomatic carriage may represent a mode of entry to symptomatic malaria, as well as transmission, especially in young children. 4,5 Malaria is a major public health problem in Ethiopia, where ~68% of the population lives in malaria-risk areas.…”