Introduction
Aedes albopictus
(Skuse) is an important vector of arboviral diseases, including dengue, chikungunya and Zika virus disease. Monitoring insecticide resistance and mechanisms by which the mosquito develops resistance is crucial to minimise disease transmission.
Aim
To determine insecticide resistance status and mechanisms in
Ae. albopictus
from different geographical regions.
Methods
We sampled 33 populations of
Ae. albopictus
from Asia, Europe and South America, and tested these for susceptibility to permethrin, a pyrethroid insecticide. In resistant populations, the target site for pyrethroids, a voltage-sensitive sodium channel (
Vssc
) was genotyped. Three resistant sub-strains, each harbouring a resistance allele homozygously, were established and susceptibilities to three different pyrethroids (with and without a cytochrome P450 inhibitor) were assayed.
Results
Most populations of
Ae. albopictus
tested were highly susceptible to permethrin but a few from Italy and Vietnam (4/33), exhibited high-level resistance. Genotyping studies detected a knockdown resistance (
kdr
) allele V1016G in
Vssc
for the first time in
Ae. albopictus
. Two previously reported
kdr
alleles, F1534C and F1534S, were also detected. The bioassays indicated that the strain homozygous for the V1016G allele showed much greater levels of pyrethroid resistance than other strains harbouring F1534C or F1534S.
Conclusion
The V1016G allele was detected in both
Asian and Italian
Ae. albopictus
populations, thus a spread of this allele beyond Italy in Europe cannot be ruled out. This study emphasises the necessity to frequently and regularly monitor the V1016G allele in
Ae. albopictus
, particularly where this mosquito species is the main vector of arboviruses.
BackgroundJars, tanks, and drums provide favorable rearing/breeding sites for Aedes aegypti in Vietnam. However, the use of insecticides to control mosquitoes at such breeding sites has not been approved in Vietnam since they are also often sources of drinking water, making larval vector control difficult. Mosquito nets pre-treated with long-lasting insecticide treated nets (LLITNs) form an effective measure for malaria control. We examined changes in the abundance of immature Aedes aegypti to evaluate the efficacy of covering ceramic jars with lids comprising one type of LLITN, Olyset® Net, in inhibiting oviposition by adult females, and to evaluate the effect of treating other breeding containers, such as flower vases, inside and around the outside of houses with a slow-release pyriproxyfen formulation to kill pupae.MethodsWe selected 313 households for the trial and 363 households for the control in Tan Chanh, Long An province, Vietnam. In the trial area, Olyset® Net lids were used to cover five major types of water container (ceramic jars, cylindrical concrete tanks, other concrete tanks, plastic drums, and plastic buckets), while pyriproxyfen was used to treat flower vases and ant traps. We also monitored dengue virus transmission by measuring anti-dengue IgM and IgG levels in healthy residents in both control and trial areas to estimate the effectiveness of Olyset® Net at controlling the dengue vector, Aedes aegypti.ResultsThe container-index and house-index for immature Ae. aegypti fell steeply one month after treatment in the trial area. Lids with Olyset® Net that fit container openings clearly seemed to reduce the presence of immature Ae. aegypti as the density of pupae decreased 1 month after treatment in the trial area. Pyriproxyfen was also effective at killing pupae in the water containers in the trial area. Although the dengue seroconversion rate was not influenced by Olyset® Net, it was lower in two-five year old children when compared to older children and adults in both control and trial areas.ConclusionsOur study showed that the treatment by Olyset® Net and pyriproxyfen had a strong negative effect on the prevalence of immature Ae. aegypti, which persisted for at least 5 months after treatment.
Tick identification is important in control of tick-born diseases because tick-borne pathogens are often transmitted by specific tick species. In this study, we determined partial DNA sequences of the mitochondrial 16S rDNA gene (mt-rrs) for ticks including 7 genera and 39 species, and these ticks were allocated to 113 sequence types. Of the 39 species of ticks, 36 species (92.3%) were distinguishable by phylogenetic analysis of mt-rrs. This result suggests that species identification of ticks based on mt-rrs is a viable alternative to morphological identification. In order to establish a DNA database for identification of ixodid and argasid ticks in Japan, we deposited all sequence data in GenBank (from AB819156 to AB819268).
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