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VECTOR CONTROL - Full susceptibility of Anopheles gambiae sensu lato against pirimiphos-methyl across Burkina Faso (2019)

Summary: After signs of reduced insecticide efficacy in controlling Anopheles gambiae sensu lato (s.l) in Burkina Faso, researchers conducted a study and determined that while there was resistance to deltamethrin, they found no resistance to pirimiphos-methyl (PPM), the active ingredient in Actellic® 300CS insecticide. 

In Burkina Faso, malaria prevention relies on long-lasting insecticidal nets (LLIN). Several million of these LLINs have been provided through mass distribution campaigns in the last decade. Additional measures have included indoor residual spraying (IRS) with bendiocarb, which was introduced in 2010 in Diébougou in southwestern Burkina Faso as part of a pilot programme terminated in 2011.1 In 2017, USAID initiated a second phase of IRS in three regions of Burkina Faso for four years. However, during entomological follow-ups, a decrease in the susceptibility of Anopheles gambiae s.l to Actellic 300CS was reported in some areas.2 

In response, researchers led by Dr. Moussa Guelbeogo, launched a study to investigate the reports. They evaluated the susceptibility of Anopheles gambiae s.l. against 11 villages treated with PPM, the active ingredient in Actellic 300CS, and 12 villages treated with deltamethrin, in three different areas: the Cascades region, the southwestern region and the northern region of Burkina Faso. The trial was performed in 2019 during malaria’s high transmission season. Mosquito larvae from several sites within each location were pooled and tests were conducted on hatched adult populations according to the World Health Organization’s (WHO) standard tube assay protocol (test of 1x, 5x, 10x of discriminating dose, n=6, 25 female mosquitoes (3-5d) per tube, one-hour exposure, 24-hour observation; WHO 2016; “Kisumu” as reference). Filter papers impregnated with either PPM or deltamethrin were provided by USM/WHO (Malaysia) and Syngenta (Switzerland).

The results showed a low mortality of all collected populations of Anopheles gambiae s.l against deltamethrin (mean mortality rate: 17% at the discriminating dose of 0.05%, 54% at 5x, and still only 78% mean mortality at the 10x concentration of 0.5%) indicating a high level of resistance against deltamethrin in all three tested areas of Burkina Faso (Figure 1). This confirms the previous observation of this level of resistance of Anopheles gambiae s.l populations to pyrethroids across the country (Namountougou et al., 2019: 10-38% mortality). Additionally, in 2010, resistance against deltamethrin was reported from four different regions in Burkina Faso (Badolo et al., 2012: 78-86% mortality).

The mean mosquito mortality from all sites against PPM was 99.8% when exposed to the standard discriminating dose of 0.25%. This strongly indicates no resistance against Actellic 300CS (Figure 2). The result aligns with previous studies in Burkina Faso (Namountougou et al., 2019: 100% mortality) and in Benin (Salako et al., 2019: 100% mortality). 

No differences between the two sources of impregnated filter papers (USM, Syngenta) were detected with the insecticides (data not shown here). 

Figure 1: 24-hour mortality of Anopheles gambiae s.l. tested against three concentrations of deltamethrin: 0.05%, 0.25% and 0.5%

Figure 2: 24-hour mortality of Anopheles gambiae s.l. tested against PPM at the discriminating dose of 0.25%. The higher concentrations (5x and 10x) were not tested.

3Badolo A et al., (2012) Three years of insecticide resistance monitoring in Anopheles gambiae in Burkina Faso: resistance on the rise? Malar J. 2012 Jul 16; 11:232.
4Namountougou M et al. (2019).  Insecticide resistance mechanisms in Anopheles gambiae complex populations from Burkina Faso, West Africa. Acta Trop. 2019 Sep;197:105054.
5Salako AS et al., (2019) Efficacy of Actellic 300 CS-based indoor residual spraying on key entomological indicators of malaria transmission in Alibori and Donga, two regions of northern Benin. Parasit Vectors. 2019 Dec 30;12(1):612


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