Malaria vector species composition and entomological indices following indoor residual spraying in regions bordering Lake Victoria, Tanzania

Abstract

Background Vector control through long-lasting insecticidal nets (LLINs) and focal indoor residual spraying (IRS) is a major component of the Tanzania national malaria control strategy. In mainland Tanzania, IRS has been conducted annually around Lake Victoria basin since 2007. Due to pyrethroid resistance in malaria vectors, use of pyrethroids for IRS was phased out and from 2014 to 2017 pirimiphos-methyl (Actellic® 300CS) was sprayed in regions of Kagera, Geita, Mwanza, and Mara. Entomological surveillance was conducted in 10 sprayed and 4 unsprayed sites to determine the impact of IRS on entomological indices related to malaria transmission risk. Methods WHO cone bioassays were conducted monthly on interior house walls to determine residual efficacy of pirimiphos-methyl CS. Indoor CDC light traps with or without bottle rotator were hung next to protected sleepers indoors and also set outdoors (unbaited) as a proxy measure for indoor and outdoor biting rate and time of biting. Prokopack aspirators were used indoors to capture resting malaria vectors. A sub-sample of Anopheles was tested by PCR to determine species identity and ELISA for sporozoite rate. Results Annual IRS with Actellic® 300CS from 2015 to 2017 was effective on sprayed walls for a mean of 7 months in cone bioassay. PCR of 2016 and 2017 samples showed vector populations were predominantly Anopheles arabiensis (58.1%, n = 4,403 IRS sites, 58%, n = 2,441 unsprayed sites). There was a greater proportion of Anopheles funestus sensu stricto in unsprayed sites (20.4%, n = 858) than in sprayed sites (7.9%, n = 595) and fewer Anopheles parensis (2%, n = 85 unsprayed, 7.8%, n = 591 sprayed). Biting peaks of Anopheles gambiae sensu lato (s.l.) followed periods of rainfall occurring between October and April, but were generally lower in sprayed sites than unsprayed. In most sprayed sites, An. gambiae s.l. indoor densities increased between January and February, i.e., 10–12 months after IRS. The predominant species An. arabiensis had a sporozoite rate in 2017 of 2.0% (95% CI 1.4–2.9) in unsprayed sites compared to 0.8% (95% CI 0.5–1.3) in sprayed sites (p = 0.003). Sporozoite rates were also lower for An. funestus collected in sprayed sites. Conclusion This study contributes to the understanding of malaria vector species composition, behaviour and transmission risk following IRS around Lake Victoria and can be used to guide malaria vector control strategies in Tanzania.

Influence of Indoor Residual Spay on An. Gambiae S.L. and An. Funestus Abundance, Resting Behavior and Community Perception on Irs Intervention In Kagera-Tanzania

“…funestus were collected indoors, despite the fact that, Missenyi district was IRS sprayed. Our findings contrast with the previous finding conducted in the lake zone Tanzania by Kakilla and others [30] which reported very low An. funestus indoor density in most sites including Missenyi district in the as evidenced by monthly mosquito collection for a period of one year in 2017.…”

“…gambiae s.l. was collected in Missenyi district post-spray with pirimiphos-methyl [30]. This disparity could be due to rapid species shift as a result of LLINs and IRS interventions implementation [36,37].…”

“…funestus in Missenyi (indoor residual sprayed district) protection and Karagwe (non-indoor residual sprayed district) in Kagera, Tanzania. Missenyi district was sprayed with pirimiphos-methyl in 2016 and 2017 with 93.7% coverage [30]. Pirimiphos-methyl (Actellic® 300CS) has been reported to have a residual efficacy beyond 9 months on oil paint wall surfaces post-IRS [31].…”

Laboratory and Greenhouse Performance of Five Commercial Light Traps for Capturing Mosquitoes in China

“…In malaria-endemic Africa, indoor control methods for the malaria vector Anopheles mosquitoes are mainly by indoor residual spraying (IRS), which usually requires implementation by professional pest control operators (Bouckenooghe et al 2019, Hamre et al 2020, Kakilla et al 2020, Lees et al 2020, Hien et al 2021. Mosquito incense and aerosols are traditional mosquito control methods in home environments in dengue-endemic Southeast Asia and southern China.…”

Laboratory and Field Performance of Five Cheap Commercial Light Traps for Capturing Mosquitoes In China

“…In malaria-endemic Africa, indoor control methods for the malaria vector Anopheles mosquitoes are mainly indoor residual spraying (IRS), which usually requires implementation by professional pest control personnel [10,11,12,13,14]. Mosquito incense and aerosols are traditional mosquito control methods in the home environment in dengue-endemic Southeast Asia and southern China.…”