Resistance intensity status of Anopheles gambiae s.l. species at KOLOKOPE, eastern plateau Togo: A potential site to assess new vector control tools

Malaria vector control in sub-Saharan Africa: complex trade-offs to combat the growing threat of insecticide resistance

Mass distribution of insecticide-treated nets (ITNs) has been a key factor in reducing malaria cases and deaths in sub-Saharan Africa. A shortcoming has been the over-reliance on pyrethroid insecticides, with more than 2·13 billion pyrethroid ITNs (PY ITNs) distributed in the past two decades, leading to widespread pyrethroid resistance. Progressive changes are occurring, with increased deployment of more effective pyrethroid-chlorfenapyr (PY-CFP) or pyrethroid-piperonyl butoxide (PY-PBO) ITNs in areas of pyrethroid resistance. In 2023, PY-PBO ITNs accounted for 58% of all ITNs shipped to sub-Saharan Africa. PY-PBO and PY-CFP ITNs are 30-37% more expensive than standard PY ITNs, equating to an additional US$132-159 million required per year in sub-Saharan Africa to fund the shift to more effective ITNs. Several countries are withdrawing or scaling back indoor residual spraying (IRS) programmes to cover the shortfall, which is reflected by the number of structures sprayed by the US President's Malaria Initiative decreasing by 30% from 5·67 million (2021) to 3·96 million (2023). Benin, located in West Africa, is a prime example of a country that ceased IRS in 2021 after 14 years of annual spraying. Our economic evaluation indicates that IRS in Benin cost $3·50 per person protected per year, around five times more per person protected per year compared with PY-PBO ($0·73) or PY-CFP ITNs ($0·76). Although costly to implement, a major advantage of IRS is the portfolio of at least three chemical classes for prospective resistance management. With loss of synergy to PBO developing rapidly, there is the danger of over-reliance on PY-CFP ITNs. As gains in global malaria control continue to reverse each year, current WHO projections estimate that key 2030 malaria incidence milestones will be missed by a staggering 89%. This Personal View explores contemporary malaria vector control trends in sub-Saharan Africa and cost implications for improved disease control and resistance management.

Physico-chemical characterization of Anopheles gambiae s.l. breeding sites and kdr mutations in urban areas of Cotonou and Natitingou, Benin

BACKGROUND

This study aimed to investigate the relationship between the physicochemical characteristics of An. gambiae s.s. and An. coluzzii breeding sites, the susceptibility profiles to commonly used insecticides in public health, and the underlying insecticide resistance mechanisms.

METHODS

Anopheles breeding sites surveys were conducted in Cotonou and Natitingou in September 2020, January and August 2021. Physicochemical properties and bacterial loads were determined in individual breeding sites. The WHO susceptibility assays were carried out using the female of the emerging adult mosquitoes. Anopheles species were identified through PCR techniques. Kdr L1014F/S, N1575Y and G119S mutations were investigated using TaqMan genotyping assays.

RESULTS

Molecular analysis showed that all mosquitoes analyzed in Cotonou were Anopheles coluzzii, while those of Natitingou were Anopheles gambiae s.s. Fecal coliforms were identified as playing a role in this distribution through their significant influence on the presence of An. coluzzii larvae. WHO susceptibility assay indicated a high level of resistance to deltamethrin in the two cities. The resistance levels to deltamethrin were higher in Cotonou (X2 = 31.689; DF = 1; P < 0.0001). There was a suspected resistance to bendiocarb in Cotonou, whereas the mosquito population in Natitingou was resistant. The kdr L1014F mutation was highly observed in both mosquito populations (frequence: 86-91%), while the Ace-1 mutation was found in a small proportion of mosquitoes. In Cotonou, salinity was the only recorded physicochemical parameter that significantly correlated with the resistance of Anopheles mosquitoes to deltamethrin (P < 0.05). In Natitingou, significant correlations were observed between the allelic frequencies of the kdr L1014F mutation and pH, conductivity, and TDS.

CONCLUSION

These results indicate a high level of pyrethroid resistance in the anopheles populations of both Cotonou and Natitingou. Moreover, this study report the involvement of abiotic factors influencing Anopheles susceptibility profile.

Development of rice farming: a cause of the emergence of multiple insecticide resistance in populations of Anopheles gambiae s.l and its impact on human health in Malanville, Bénin

Aim

The rise in rice production in the district of Malanville, Northen Benin, is a present concern, as it has resulted in the widespread usage of pesticides for crop protection. This could impact human health but also life cycle of Anopheles gambiae, the main vector of malaria.

Methods

Therefore, insecticide susceptibility bioassays were carried out on populations of An. gambiae s.l aged to 3-5 days old (two from areas where insecticide is highly used and other two areas of low insecticide use) and subjected to insecticide-impregnated papers (Permethrin 0.75%; deltamethrin 0.05%; DDT 4% and bendiocarb 0.1%) following WHO protocol. Polymerase Chain Reactions (PCRs) were used for the detection of Acethlylcholinestrase (Ace-1) and the knock down resistance (kdr) L1014F mutations in An. gambiae populations. Finally, indirect bioassays were conducted for the investigating on the factors affecting the life cycle of An. gambiae due to the use of pesticides.

Results

An. gambiae from the four sites were resistant to DDT (6 to 8% and 10 to 14% respectively from areas of high and low dose), pyrethroids (22 to 26% and 30 to 36% for permethrin, from areas of high and low dose respectively and 66 to 70% and 72 to 80% for deltamethrin, from high and low dose) but susceptible to carbamate. The kdr L1014F mutation was detected in An. gambiae populations (0.88 to 0.90 and 0.84 to 0.88 from high and low dose, respectively). The ace-1 was detected at low frequencies (<0.002). Bioassays on the impacts of the use of pesticides in the life cycle of An. gambiae showed that soil substrates with pesticides residues have a negative impact on the life cycle eggs of An. gambiae.

Conclusion

These findings confirmed the negative impacts of pesticides use in rice farming and its impacts on the life cycle of An. gambiae.

Insecticide resistance intensity and efficacy of synergists with pyrethroids in Anopheles gambiae (Diptera: Culicidae) from Southern Togo

BACKGROUND

This study was designed to provide insecticide resistance data for decision-making in terms of resistance management plans in Togo.

METHODS

The susceptibility status of Anopheles gambiae sensu lato (s.l.) to insecticides used in public health was assessed using the WHO tube test protocol. Pyrethroid resistance intensity bioassays were performed following the CDC bottle test protocol. The activity of detoxification enzymes was tested using the synergists piperonyl butoxide, S.S.S-tributlyphosphorotrithioate and ethacrinic acid. Species-specific identification of An. gambiae s.l. and kdr mutation genotyping were performed using PCR techniques.

RESULTS

Local populations of An. gambiae s.l. showed full susceptibility to pirimiphos methyl at Lomé, Kovié, Anié, and Kpèlè Toutou. At Baguida, mortality was 90%, indicating possible resistance to pirimiphos methyl. Resistance was recorded to DDT, bendiocarb, and propoxur at all sites. A high intensity of pyrethroid resistance was recorded and the detoxification enzymes contributing to resistance were oxidases, esterases, and glutathione-s-transferases based on the synergist tests. Anopheles gambiae sensu stricto (s.s.) and Anopheles coluzzii were the main species identified. High kdr L1014F and low kdr L1014S allele frequencies were detected at all localities.

CONCLUSION

This study suggests the need to reinforce current insecticide-based malaria control interventions (IRS and LLINs) with complementary tools.