A cohort study of Plasmodium falciparum infection dynamics in Western Kenya Highlands

Abstract

BackgroundThe Kenyan highlands were malaria-free before the 1910s, but a series of malaria epidemics have occurred in the highlands of western Kenya since the 1980s. Longitudinal studies of the genetic structure, complexity, infection dynamics, and duration of naturally acquired Plasmodium falciparum infections are needed to facilitate a comprehensive understanding of malaria epidemiology in the complex Kenyan highland eco-epidemiological systems where malaria recently expanded, as well as the evaluation of control measures.MethodsWe followed a cohort of 246 children residing in 3 villages at altitudes 1430 - 1580 m in western Kenya. Monthly parasitological surveys were undertaken for one year, yielding 866 P. falciparum isolates that were analyzed using 10 microsatellite markers.ResultsInfection complexity and genetic diversity were high (HE = 0.787-0.816), with ≥83% of infections harboring more than one parasite clone. Diversity remained high even during the low malaria transmission season. There was no significant difference between levels of genetic diversity and population structure between high and low transmission seasons. Infection turn-over rate was high, with the average infection duration of single parasite genotypes being 1.11 months, and the longest genotype persistence was 3 months.ConclusionsThese data demonstrate that despite the relatively recent spread of malaria to the highlands, parasite populations seem to have stabilized with no evidence of bottlenecks between seasons, while the ability of residents to clear or control infections indicates presence of effective anti-plasmodial immune mechanisms.

The evolution of drug resistance and the curious orthodoxy of aggressive chemotherapy

“…A substantial body of epidemiological evidence is consistent with crowding effects within infections, whereby the population densities of individual genotypes are suppressed when other genotypes are present (15,16,(23)(24)(25)(26)(27)(28)(29)(30)(31). For example, parasite densities are unrelated to the number of clones per host, and high turnover rates are observed in mixed-genotype infections.…”

The fitness of drug‐resistant malaria parasites in a rodent model: multiplicity of infection

“…However, correlational field data are consistent with suppression of parasite genotypes when other genotypes are present (e.g. Daubersies et al, 1996;Mercereau-Puijalon, 1996;Smith et al, 1999;Bruce et al, 2000;Hastings, 2003;Talisuna et al, 2006;Bousema et al, 2008;Farnert, 2008;Harrington et al, 2009;Baliraine et al, 2010). Additionally, there is considerable direct experimental evidence for crowding in rodent malaria models (e.g.…”

“…One important complexity which we did not study here is the situation where multi-genotype infections arise from multiple infectious bites days or weeks apart. A turn-over of different parasite clones has frequently been observed in the field (Daubersies et al, 1996;Bruce et al, 2000;Farnert, 2008;Baliraine et al, 2010). The dynamics following such super-infections may result in different competitive outcomes, whereby competition may be more intense for genotypes that infect later on in the infection (de Roode et al, 2005a).…”

Progress towards understanding the ecology and epidemiology of malaria in the western Kenya highlands: Opportunities and challenges for control under climate change risk

“…Furthermore no differences were found in the gene mutation frequency between asymptomatic and symptomatic cases (Zhong et al, 2008). Analysis of 10 microsatellite markers from P. falciparum samples obtained from the highlands of western Kenya indicated high genetic diversity in the population and lack of any bottlenecks (Baliraine et al, 2010). …”