title: Experimental study of the relationship between Plasmodium gametocyte density and infection success in mosquitoes; implications for the evaluation of malaria transmission-reducing interventions.
abstract: The evaluation of transmission reducing interventions (TRI) to control malaria widely uses membrane feeding assays. In such assays, the intensity of Plasmodium infection in the vector might affect the measured efficacy of the candidates to block transmission. Gametocyte density in the host blood is a determinant of the infection success in the mosquito, however, uncertain estimates of parasite densities and intrinsic characteristics of the infected blood can induce variability. To reduce this variation, a feasible method is to dilute infectious blood samples. We describe the effect of diluting samples of Plasmodium-containing blood samples to allow accurate relative measures of gametocyte densities and their impact on mosquito infectivity and TRI efficacy. Natural Plasmodium falciparum samples were diluted to generate a wide range of parasite densities, and fed to Anopheles coluzzii mosquitoes. This was compared with parallel dilutions conducted on Plasmodium berghei infections. We examined how blood dilution influences the observed blocking activity of anti-Pbs28 monoclonal antibody using the P. berghei/Anopheles stephensi system. In the natural species combination P. falciparum/An. coluzzii, blood dilution using heat-inactivated, infected blood as diluents, revealed positive near linear relationships, between gametocyte densities and oocyst loads in the range tested. A similar relationship was observed in the P. berghei/An. stephensi system when using a similar dilution method. In contrast, diluting infected mice blood with fresh uninfected blood dramatically increases the infectiousness. This suggests that highly infected mice blood contains inhibitory factors or reduced blood moieties, which impede infection and may in turn, lead to misinterpretation when comparing individual TRI evaluation assays. In the lab system, the transmission blocking activity of an antibody specific for Pbs28 was confirmed to be density-dependent. This highlights the need to carefully interpret evaluations of TRI candidates, regarding gametocyte densities in the P. berghei/An. stephensi system.
authors.affiliation: Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, Bobo Dioulasso 01 01 BP 545, Burkina Faso; Institut de Recherche pour le Développement, unité MIVEGEC (UM1-UM2-CNRS 5290-IRD 224), 911 avenue Agropolis, Montpellier Cedex 5 34394, France.
authors.forename: Dari F
authors.initials: DF
authors.lastname: Da
authors.affiliation: Department of Infectious Disease Epidemiology, Imperial College London, London, United Kingdom.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Churcher
authors.affiliation: Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, Bobo Dioulasso 01 01 BP 545, Burkina Faso.
authors.forename: Rakiswendé S
authors.initials: RS
authors.lastname: Yerbanga
authors.affiliation: Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, Bobo Dioulasso 01 01 BP 545, Burkina Faso.
authors.forename: Bienvenue
authors.initials: B
authors.lastname: Yaméogo
authors.affiliation: Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, Bobo Dioulasso 01 01 BP 545, Burkina Faso; Institut de Recherche pour le Développement, unité MIVEGEC (UM1-UM2-CNRS 5290-IRD 224), 911 avenue Agropolis, Montpellier Cedex 5 34394, France.
authors.forename: Ibrahim
authors.initials: I
authors.lastname: Sangaré
authors.affiliation: Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, Bobo Dioulasso 01 01 BP 545, Burkina Faso.
authors.forename: Jean Bosco
authors.initials: JB
authors.lastname: Ouedraogo
authors.affiliation: Division of Cell and Molecular Biology, Imperial College London, London, United Kingdom; The Jenner Institute, University of Oxford, Roosevelt Drive, Oxford OX3 7DQ, United Kingdom.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Sinden
authors.affiliation: Division of Cell and Molecular Biology, Imperial College London, London, United Kingdom.
authors.forename: Andrew M
authors.initials: AM
authors.lastname: Blagborough
authors.affiliation: Institut de Recherche en Sciences de la Santé, Direction Régionale, 399 avenue de la liberté, Bobo Dioulasso 01 01 BP 545, Burkina Faso; Institut de Recherche pour le Développement, unité MIVEGEC (UM1-UM2-CNRS 5290-IRD 224), 911 avenue Agropolis, Montpellier Cedex 5 34394, France. Electronic address: anna.cohuet@ird.fr.
authors.forename: Anna
authors.initials: A
authors.lastname: Cohuet
mesh_terms: D000818:Animals; D000852:Anopheles / Q000469:parasitology*; D002353:Carrier State / Q000469:parasitology; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007303:Insect Vectors / Q000469:parasitology*; D008288:Malaria / Q000469:parasitology / Q000635:transmission; D016778:Malaria, Falciparum / Q000469:parasitology / Q000635:transmission*; D051379:Mice; D010962:Plasmodium berghei / Q000254:growth & development*; D010963:Plasmodium falciparum / Q000254:growth & development*
keywords: Anopheles; Dilution; Gametocyte density; Infection success; Plasmodium; Transmission blocking interventions