Showing papers by "Shinji Kasai published in 2021"

A first, naturally occurring substitution at the second pyrethroid receptor of voltage-gated sodium channel of Aedes aegypti.

Abstract: BACKGROUND Aedes aegypti is a remarkably effective mosquito vector of epidemiologically important arboviral diseases including dengue fever, yellow fever and Zika The present spread of resistance against pyrethroids, the primary insecticides used for mosquito control, in global populations of this species is of great concern The voltage-gated sodium channel (VGSC) in the nervous system is the known target site of pyrethroids in insects Past studies have revealed several amino-acid substitutions in this channel that confer pyrethroid resistance, which are known as knockdown resistance (kdr) mutations RESULTS This study investigated a laboratory colony of Ae aegypti, MCNaeg, established from larvae collected in Rio de Janeiro, Brazil in 2016 The MCNaeg colony showed strong resistance against pyrethroids without laboratory selection Of the two VGSC gene haplotypes present within this colony, one harbored three known kdr mutations, V410L, V1016I, and F1534C, and the other harbored only the known F1534C mutation In latter haplotype, we also found novel amino-acid substations including V253F Previous molecular modeling and electrophysiological studies suggest that this residue serves a pyrethroid-sensing site in the second receptor, PyR2 Our genetical analysis showed that the haplotype harboring V253F and F1534C is associated with equal or slightly stronger resistance than the other triple kdr haplotype to both Type I and Type II pyrethroids CONCLUSION The novel substitution V253F is potentially involved in pyrethroid resistance in Ae aegypti Further studies are needed to elucidate the role of this substitution in the pyrethroid susceptibility of VGSC © 2021 The Authors Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry

Determining vector competence of Aedes aegypti from Ghana in transmitting dengue virus serotypes 1 and 2.

Abstract: Dengue virus (DENV) is a mosquito-borne arbovirus transmitted by Aedes mosquitoes, but is not endemic in all areas where this vector is found. For example, the relatively sparse distribution of cases in West Africa is generally attributed to the refractory nature of West African Aedes aegypti (Ae. aegypti) to DENV infection, and particularly the forest-dwelling Ae. aegypti formosus. However, recent studies have shown these mosquitoes to be competent vectors within some West African countries that have suffered outbreaks in the past, such as Senegal. There is however little information on the vector competence of the Ae. aegypti in West African countries such as Ghana with no reported outbreaks. This study examined the vector competence of 4 Ae. aegypti colonies from urban, semi-urban, and two rural locations in Ghana in transmitting DENV serotypes 1 and 2, using a single colony from Vietnam as control. Midgut infection and virus dissemination were determined by quantitative reverse transcription polymerase chain reaction (qRT-PCR), while the presence and concentration of DENV in the saliva of infectious mosquitoes was determined by the focus forming assay. There were significant differences in the colonies’ susceptibility to virus infection, dissemination, and transmission. All examined Ghanaian mosquitoes were refractory to infection by DENV serotype 2, while some colonies exhibited potential to transmit DENV serotype 1. None of the tested colonies were as competent as the control group colony. These findings give insight into the possible risk of outbreaks, particularly in the urban areas in the south of Ghana, and highlight the need for continuous surveillance to determine the transmission status and outbreak risk. This study also highlights the need to prevent importation of different DENV strains and potential invasion of new highly vector-competent Ae. aegypti strains, particularly around the ports of entry.

Novel CONCOMITANT mutations L932F and I936V in the Voltage-Gated Sodium Channel and Its Association With Pyrethroid Resistance in Culex quinquefasciatus (Diptera: Culicidae).

Abstract: Highly residual pyrethroids such as permethrin have been used for controlling mosquitoes that transmit infectious diseases. However, the selective pressure from such insecticides may result in cross-resistance against other pyrethroids used for household insecticides. In this study, we investigated the susceptibility of Culex quinquefasciatus Say collected from Brazil and Myanmar to permethrin in addition to four types of household pyrethroids. Both strains exhibited high resistance against all pyrethroids tested, indicating cross-resistance. Furthermore, we detected the knockdown resistance (kdr) mutations L932F+I936V in the voltage-gated sodium channel gene (VGSC) in the Brazilian strain. Notably, the L932F+I936V haplotype has previously been observed in in silico data, but it should be detected not directly from living insects. In comparison, a common kdr mutation, L1014F, was detected from the Myanmar strain. Although L1014F was also detected from the Brazilian strain, the allele frequency was too low to affect resistance. Both strains harbored the resistance-associated haplotypes of the cytochrome P450 gene, CYP9M10. The Brazilian strain demonstrated comparable resistance against pyrethroids as that of the Myanmar strain even when a cytochrome P450 inhibitor, piperonyl butoxide was added to the bioassay. Our results suggested that the L932F+I936V mutations confer the Brazilian strain of Cx. Quiquefasciatus with resistance at a comparable level to that conferred by the well-recognized kdr mutation L1014F in the Myanmar strain. The identification of unexplored mutations may improve the diagnosis and understanding of resistance of this medically important species.