Togetherness among Plasmodium falciparum gametocytes: interpretation through simulation and consequences for malaria transmission.
Previous experimental gametocyte infections of Anopheles arabiensis on 3 volunteers naturally infected with Plasmodium falciparum were conducted in Senegal. They showed that gametocyte counts in the mosquitoes are, like macroparasite intakes, heterogeneous (overdispersed). They followed a negative binomial distribution, the overdispersion coefficient seeming constant (k = 3.1). To try to explain this heterogeneity, we used an individual-based model (IBM), simulating the behaviour of gametocytes in the human blood circulation and their ingestion by mosquitoes. The hypothesis was that there exists a clustering of the gametocytes in the capillaries. From a series of simulations, in the case of clustering the following results were obtained: (i) the distribution of the gametocytes ingested by the mosquitoes followed a negative binomial, (ii) the k coefficient significantly increased with the density of circulating gametocytes. To validate this model result, 2 more experiments were conducted in Cameroon. Pooled experiments showed a distinct density dependency of the k-values. The simulation results and the experimental results were thus in agreement and suggested that an aggregation process at the microscopic level might produce the density-dependent overdispersion at the macroscopic level. Simulations also suggested that the clustering of gametocytes might facilitate fertilization of gametes.
Gaillard
F O
FO
Institut de Recherche pour le Développement (IRD), UR 79, Geodes, Bondy, France.
Boudin
C
C
Chau
N P
NP
Robert
V
V
Pichon
G
G
D000330:Aedes / Q000469:parasitology*; D000818:Animals; D016010:Binomial Distribution; D003198:Computer Simulation; D005260:Female; D005718:Gametogenesis / Q000502:physiology; D006801:Humans; D007303:Insect Vectors / Q000469:parasitology*; D016778:Malaria, Falciparum / Q000469:parasitology / Q000635:transmission*; D008297:Male; D008954:Models, Biological; D010963:Plasmodium falciparum / Q000254:growth & development*