Spatial distribution of insecticide resistant Check update populations of Aedes aegypti and Ae. albopictus and first detection of V410L mutation in Ae. aegypti from Cameroon

Background:Dengue(DENV),chikungunya(CHIKV)and Zika virus(ZIKV),are mosquito-borne viruses of medical importance in most tropical and subtropical regions.Vector control,primarily through insecticides,remains the primary method to prevent their transmission.Here,we evaluated insecticide resistance profles and identifed important underlying resistance mechanisms in populations of Aedes aegypti and Ae.albopictus from six different regions in Cameroon to pesticides commonly used during military and civilian public health vector control operations.Methods:Aedes mosquitoes were sampled as larvae or pupae between August 2020 and July 2021 in six locations across Cameroon and reared until the next generation,G1.Ae.aegypti and Ae.albopictus adults from G1 were tested following World Health Organization(WHO)recommendations and Ae.aegypti GO adults screened with real time melting curve qPCR analyses to genotype the F1534C,V1016l and V410L Aedes kdr mutations.Piperonyl butoxide(PBO)assays and real time qPCR were carried out from some cytochrome p450 genes known to be involved in metabolic resistance.Statistical analyses were performed using Chi-square test and generalized linear models.Results:Loss of susceptibility was observed to all insecticides tested.Mortality rates from tests with 0.25%permethrin varied from 24.27%to 85.89%in Ae.aegypti and from 17.35%to 68.08%in Ae.albopictus.Mortality rates for 0.03%deltamethrin were between 23.30%and 88.20%in Ae.aegypti and between 69.47%and 84.11%in Ae.albopictus.We found a moderate level of resistance against bendiocarb,with mortality rates ranging from 69.31%to 90.26%in Ae.aegypti and from 86.75%to 98.95%in Ae.albopictus.With PBO pre-exposure,we found partial or fully restored suscepti bility to pyrethroids and bendiocarb.The genes Cyp9M6F88/87 and Cyp9J10 were overexpressed in Ae.aegypti populations from Douala sites resistant to permethrin and deltamethrin.Cyp6P12 was highly expressed in alphacypermethrin and permethrin resistant Ae.albopictus samples.F1534C and V1016l mutations were detected in A.aegypti mosquitoes and for the first time V410L was reported in Cameroon.Conclusions:This study revealed that Ae.aegypti and Ae albopictus are resistant to multiple insecticide classes with multiple resistance mechanisms implicated.These findings could guide insecticide use to control arbovirus vectors in Cameroon.

Contrasting resistance patterns to type Ⅰ and Ⅱ pyrethroids in two major arbovirus vectors Aedes aegypti and Aedes albopictus in the Republic of the Congo, Central Africa

Background:In the Republic of Congo,with two massive outbreaks of chikungunya observed this decade,little is known about the insecticide resistance profile of the two major arbovirus vectors Aedes aegypti and Aedes albopictus.Here,we established the resistance profile of both species to insecticides and explored the resistance mechanisms to help Congo to better prepare for future outbreaks.Methods:Immature stages o f Ae.aegypti and Ae.albopictus were sampled in May 2017 in eight cities of the Republic of the Congo and reared to adult stage.Larval and adult bioassays,and synergist(piperonyl butoxide[PBO])assays were carried out according to WHO guidelines.F1534C mutation was genotyped in field collected adults in both species and the polymorphism of the sodium channel gene assessed in Ae.oegypti.Results:All tested populations were susceptible to temephos after larval bioassays.A high resistance level was observed to 4%DDT in both species countrywide(21.9-88.3% mortality).All but one population(Ae.oegypti from Ngo)exhibited resistance to type I pyrethroid,permethrin,but showed a full susceptibility to type II pyrethroid(deltamethrin)in almost all locations.Resistance was also reported to 1% propoxur in Ae.aegypti likewise in two Ae.albopictus populations(Owando and Ouesso),and the remaining were fully susceptible.All populations of both species were fully susceptible to 1%fenitrothion.A full recovery of susceptibility was observed in Ae.oegypti and Ae.albopictus when pre-exposed to PBO and then to propoxur and permethrin respectively.The F1534C kdr mutation was not detected in either species.The high genetic variability of the portion of sodium channel spanning the F1534C in Ae.aegypti further supported that knockdown resistance probably play no role in the permethrin resistance.Conclusions:Our study showed that both Aedes species were susceptible to organophosphates(temephos and fenitrothion),while for other insecticide classes tested the profile of resistance vary according to the population origin.These findings could help to implement better and efficient strategies to control these species in the Congo in the advent of future arbovirus outbreaks.

First detection of F1534C knockdown resistance mutation in Aedes aegypti(Diptera:Culicidae)from Cameroon

Background: Aedes borne viral diseases,notably dengue,are increasingly reported in Cameroon with Aedes aegypti being a major vector.Data on insecticide resistance of this vector and underlying mechanisms needed for outbreak preparedness remain scarce in Cameroon.Here,we present the nationwide distribution of insecticide resistance in Ae.aegypti and investigate the potential resistance mechanisms involved.Methods:: Immature stages of Ae.aegypti were collected between March and July 2017 in 13 locations across Cameroon and reared until G1/G2/G3 generation.Larval,adult bioassays,and piperonyl butoxide(PBO)synergist assays were carried out according to World Health Organization guidelines.F1534C mutation was genotyped using allele specific polymerase chain reaction in field collected adults(Go)and the polymorphism of the sodium channel gene was assessed.Theχ2 test was used to compare the mortality rate between bioassays with insecticides only and bioassays after preexposure to PBO synergist.Results: Larval bioassay revealed that all the three populations tested with temephos were susceptible.Adult bioassays showed a good level of susceptibility toward both pyrethroids tested,0.25%permethrin and 0.05%deltamethrin,with six out of 10 populations susceptible.However,two populations(Douala and Edéa)were resistant(deltamethrin[73.2–92.5%mortality],permethrin[2.6–76.3%mortality]).The resistance to 4%dichlorodiphenyltrichloroethane was observed in four out of 10 populations tested(16.8–87.1%mortality).Resistance was also reported to carbamates including 0.1%propoxur(60.8–87.1%mortality)and to 0.1%bendiocarb(82.9%mortality).All populations tested were fully susceptible to 1%fenitrothion.A partial recovery of susceptibility was observed in the pyrethroid resistant population of Douala after pre-exposed to PBO suggesting the implication of cytochrome P450 monoxygenases permethrin resistance.Genotyping and sequencing detected the F1534C kdr mutation in the two pyrethroid resistant locations of Edéa and Douala,with allelic frequency of 3.3%and 33.3%respectively.However,the high genetic diversity of the sodium channel gene supports the recent introduction of this mutation in Cameroon.Conclusions: This study revealed the contrasting resistance profiles to insecticides of Ae.aegypti populations in Cameroon suggesting that,instead of a unique nationwide control approach,a regionally adapted strategy will be needed to control this vector.The localised distribution of the F1534C kdr mutation supports this region-specific control strategy.