Contrasting effects of the alkaloid ricinine on the capacity of Anopheles gambiae and Anopheles coluzzii to transmit Plasmodium falciparum

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Résumé

Background: Besides feeding on blood, females of the malaria vector Anopheles gambiae sensu lato readily feed on
natural sources of plant sugars. The impact of toxic secondary phytochemicals contained in plant-derived sugars on
mosquito physiology and the development of Plasmodium parasites remains elusive. The focus of this study was to
explore the influence of the alkaloid ricinine, found in the nectar of the castor bean Ricinus communis, on the ability of
mosquitoes to transmit Plasmodium falciparum.
Methods: Females of Anopheles gambiae and its sibling species Anopheles coluzzii were exposed to ricinine through
sugar feeding assays to assess the effect of this phytochemical on mosquito survival, level of P. falciparum infection
and growth rate of the parasite.
Results: Ricinine induced a significant reduction in the longevity of both Anopheles species. Ricinine caused acceleration in the parasite growth rate with an earlier invasion of the salivary glands in both species. At a concentration
of 0.04 g l−1 in An. coluzzii, ricinine had no effect on mosquito infection, while 0.08 g l−1 ricinine-5% glucose solution
induced a 14% increase in An. gambiae infection rate.
Conclusions: Overall, our findings reveal that consumption of certain nectar phytochemicals can have unexpected
and contrasting effects on key phenotypic traits that govern the intensity of malaria transmission. Further studies will
be required before concluding on the putative role of ricinine as a novel control agent, including the development of
ricinine-based toxic and transmission-blocking sugar baits. Testing other secondary phytochemicals in plant nectar will
provide a broader understanding of the impact which plants can have on the transmission of vector-borne diseases.

Mots-clés

Plasmodium falciparum, Anopheles coluzzii, Anopheles gambiae, Ricinine, Malaria transmission, Transmission-blocking strategies