High Plasmodium infection intensity in naturally infected malaria vectors in Africa

• Published in: International journal for parasitology 2020-10, Vol.50 (12), p.985-996
• Main Authors: Bompard, Anais, Da, Dari F., Yerbanga, Serge R., Morlais, Isabelle, Awono-Ambéné, Parfait H., Dabiré, Roch K., Ouédraogo, Jean Bosco, Lefèvre, Thierry, Churcher, Thomas S., Cohuet, Anna
• Format: Article
• Language: English
• Subjects: Life Sciences; Malaria; Oocyst load; Single-feed infection load; Sporozoite rate; Transmission dynamics; Transmission-blocking vaccines; Wild mosquitoes
• ISSN: 0020-7519; 1879-0135
• DOI: 10.1016/j.ijpara.2020.05.012

[Display omitted] •A year-long analysis of malaria parasite transmission in highly endemic areas was undertaken.•The oocyst load in mosquitoes was higher than expected (average 10 oocysts/mosquitoes).•Using a transmission model we found the number of oocysts per infectious blood meal.•This number (single-feed infection load) varied with season from three to 24 oocysts.•Malaria prevalence in humans can be used to approximate the single-feed infection load. The population dynamics of human to mosquito malaria transmission in the field has important implications for the genetics, epidemiology and control of malaria. The number of oocysts in oocyst-positive mosquitoes developing from a single, naturally acquired infectious blood meal (herein referred to as a single-feed infection load) greatly influences the efficacy of transmission blocking interventions but still remains poorly documented. During a year-long analysis of malaria parasite transmission in Burkina Faso we caught and dissected wild malaria vectors to assess Plasmodium oocyst prevalence and load (the number of oocysts counted in mosquitoes with detectable oocysts) and the prevalence of salivary gland sporozoites. This was compared with malaria endemicity in the human population, assessed in cross-sectional surveys. Data were analysed using a novel transmission mathematical model to estimate the per bite transmission probability and the average single-feed infection load for each location. The observed oocyst load and the estimated single-feed infection load in naturally infected mosquitoes were substantially higher than previous estimates (means ranging from 3.2 to 24.5 according to seasons and locations) and indicate a strong positive association between the single-feed infection load and parasite prevalence in humans. This work suggests that highly infected mosquitoes are not rare in the field and might have a greater influence on the epidemiology and genetics of the parasite, and on the efficacy of novel transmission blocking interventions.