Abstract
BackgroundThe sterile insect technique (SIT) is a vector control strategy relying on the mass release of sterile males into wild vector populations. Current sex separation techniques are not fully efficient and could lead to the release of a small proportion of females. It is therefore important to evaluate the effect of irradiation on the ability of released females to transmit pathogens. This study aimed to assess the effect of irradiation on the survival and competence of Anopheles arabiensis females for Plasmodium falciparum in laboratory conditions.MethodsPupae were irradiated at 95 Gy of gamma-rays, and emerging females were challenged with one of 14 natural isolates of P. falciparum. Seven days post-blood meal (dpbm), irradiated and unirradiated-control females were dissected to assess the presence of oocysts, using 8 parasite isolates. On 14 dpbm, sporozoite dissemination in the head/thorax was also examined, using 10 parasites isolates including 4 in common with the 7 dpbm dissection (oocyst data). The survivorship of irradiated and unirradiated-control mosquitoes was monitored.ResultsOverall, irradiation reduced the proportion of mosquitoes infected with the oocyst stages by 17% but this effect was highly inconsistent among parasite isolates. Secondly, there was no significant effect of irradiation on the number of developing oocysts. Thirdly, there was no significant difference in both the sporozoite infection rate and load between the irradiated and unirradiated-control mosquitoes. Fourthly, irradiation had varying effects on female survival with either a negative effect or no effect.ConclusionsThe effect of irradiation on mosquito competence strongly varied among parasite isolates. Because of such isolate variability and, the fact that different parasite isolates were used to collect oocyst and sporozoite data, the irradiation-mediated reduction of oocyst prevalence was not confirmed for the sporozoite stages. Our data indicate that irradiated female An. arabiensis could contribute to malaria transmission, and highlight the need for perfect sexing tools, which would prevent the release of females as part of SIT programmes.
Highlights
The sterile insect technique (SIT) is a vector control strategy relying on the mass release of sterile males into wild vector populations
This study aimed to evaluate the effect of a sterilizing dose of gamma-rays from a Caesium-137 source on mosquito competence using the parasite P. falciparum, responsible for causing the most severe form of human malaria, and the mosquito An. arabiensis, a major vector of P. falciparum in Africa
Experiment 1: Effect of irradiation on An. arabiensis competence for P. falciparum Oocyst prevalence and intensity at day 7 post‐blood meal Irradiation reduced the proportion of infected mosquitoes by 16.8% (180 infected unirradiated-control mosquitoes/378 = 47.6%; and 152 infected irradiated mosquitoes/383 = 39.6%; likelihood ratio tests (LRT) χ21 = 5.2, P = 0.02; Fig. 1a)
Summary
The sterile insect technique (SIT) is a vector control strategy relying on the mass release of sterile males into wild vector populations. Since 2015 global progress has stalled, and several African countries are currently experiencing an increase in malaria incidence [3] The reasons for these recent increases are unclear but current vector control techniques are showing some limitations. SIT relies on the massive production of sterile males by irradiation or chemical treatment and introduction into wild insect populations in order to reduce the number of adults in subsequent generations [8,9,10] With repeated release, this approach has proven successful in eliminating some agricultural pest species [11], and has shown to be promising in suppressing or reducing the density of disease vectors from islands [12] or from relatively isolated areas such as urban settings [13]. It allowed the elimination of two partially isolated populations of Aedes albopictus in Guangzhou, China, when used in combination with the incompatible insect technique [14]
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