BackgroundThe Asian tiger mosquito, Aedes albopictus, is one of the 100 worst invasive species in the world and the vector for several arboviruses including dengue, Zika and chikungunya viruses. Understanding the population spatial genetic structure, migration, and gene flow of vector species is critical to effectively preventing and controlling vector-borne diseases. Little is known about the population structure and genetic differentiation of native Ae. albopictus in China. The aim of this study was to examine the patterns of the spatial genetic structures of native Ae. albopictus populations, and their relationship to dengue incidence, on a large geographical scale.MethodsDuring 2016–2018, adult female Ae. albopictus mosquitoes were collected by human landing catch (HLC) or human-bait sweep-net collections in 34 localities across China. Thirteen microsatellite markers were used to examine the patterns of genetic diversity, population structure, and gene flow among native Ae. albopictus populations. The correlation between population genetic indices and dengue incidence was also examined.ResultsA total of 153 distinct alleles were identified at the 13 microsatellite loci in the tested populations. All loci were polymorphic, with the number of distinct alleles ranging from eight to sixteen. Genetic parameters such as PIC, heterozygosity, allelic richness and fixation index (FST) revealed highly polymorphic markers, high genetic diversity, and low population genetic differentiation. In addition, Bayesian analysis of population structure showed two distinct genetic groups in southern-western and eastern-central-northern China. The Mantel test indicated a positive correlation between genetic distance and geographical distance (R2 = 0.245, P = 0.01). STRUCTURE analysis, PCoA and GLS interpolation analysis indicated that Ae. albopictus populations in China were regionally clustered. Gene flow and relatedness estimates were generally high between populations. We observed no correlation between population genetic indices of microsatellite loci in Ae. albopictus populations and dengue incidence.ConclusionStrong gene flow probably assisted by human activities inhibited population differentiation and promoted genetic diversity among populations of Ae. albopictus. This may represent a potential risk of rapid spread of mosquito-borne diseases. The spatial genetic structure, coupled with the association between genetic indices and dengue incidence, may have important implications for understanding the epidemiology, prevention, and control of vector-borne diseases.
Aedes albopictus is a vector of over 20 arboviruses that has spread throughout the world, mainly in the second half of the twentieth century. Approximately 50–100 million people are infected with dengue virus (DENV) transmitted by Aedes mosquitoes each year, leading to heavy economic burdens for both governments and individuals, among countless other negative consequences. Understanding the vector competence of vector species is critical for effectively preventing and controlling vector-borne diseases. Accordingly, in this study, vector competence was evaluated by quantitative analysis of DENV-2 loads in mosquito tissues (midguts, heads, and salivary glands) and whole mosquitoes through real-time quantitative polymerase chain reaction (RT-qPCR) analysis. Wolbachia and the expression of immune-associated genes (Rel1, Rel2, Dicer2, and STAT) in mosquitoes were also detected by RT-qPCR to explore their impact on vector competence. The amount of DENV-2 in the mosquito midguts, heads, and salivary glands from southern-western China were found to be lower than those from eastern-central-northern China. The DENV-2 loads in whole mosquitoes showed a negative correlation with Rel1 gene (r = -0.285, P = 0.011) and STAT gene expression levels (r = -0.289, P = 0.009). In terms of Wolbachia strains, the density of the wAlbB strain was found to be significantly higher than that of the wAlbA strain in the eight Ae. albopictus populations, and the relative density of the wAlbB strain in mosquitoes from southern-western China was higher than those from eastern-central-northern China. The relative density of the wAlbB strain showed a negative correlation with the mean loads of DENV-2 in the heads (r = -0.729, P = 0.040), salivary glands (r = -0.785, P = 0.021), and whole mosquitoes (r = -0.909, P = 0.002). Thus, there are lower DENV-2 loads in the mosquitoes from southern-western China, which may be related to the innate immunity of mosquitoes as affected by Rel1 in the Toll pathway, STAT in the JAK-STAT pathway, and the relative density of the wAlbB strain.
Aedes albopictus (Ae. albopictus), an important vector of dengue virus (DENV), is distributed worldwide. Identifying host proteins involved in flavivirus replication in Ae. albopictus and determining their natural antiviral mechanisms are critical to control virus transmission. Revealing the key proteins related to virus replication and exploring the host-pathogen interaction are of great significance in finding new pathways of the natural immune response in Ae. albopictus. Isobaric tags for relative and absolute quantification (iTRAQ) was used to perform a comparative proteomic analysis between the midgut of Ae. albopictus infected with DENV and the control. 3,419 proteins were detected, of which 162 were ≥ 1.2-fold differentially upregulated or ≤ 0.8-fold differentially downregulated (p < 0.05) during DENV infections. Differentially expressed proteins (DEPs) were mainly enriched in ubiquitin ligase complex, structural constituent of cuticle, carbohydrate metabolism, and lipid metabolism pathways. We found that one of the DEPs, a putative pupal cuticle (PC) protein could inhibit the replication of DENV and interact with the DENV-E protein. In addition, the result of immunofluorescence (IF) test showed that there was co-localization between ubiquitin carboxyl-terminal hydrolase (UCH) protein and the DENV-E protein, and virus infection reduced the level of this protein. iTRAQ-based proteomic analysis of the Ae. albopictus midgut identified dengue infection-induced upregulated and downregulated proteins. The interaction between the PC and UCH proteins in the midgut of Ae. albopictus might exert a natural antiviral mechanism in mosquito.
Background: As a vector of over 20 arboviruses, Aedes albopictus has spread throughout the world mostly since the second half of the twentieth century, and it is now found on every continent except Antarctica. Approximately 50-100 million people are infected with dengue virus (DENV) transmitted by Aedes mosquitoes each year, leading to a heavy economic burden on both governments and individuals. Understanding the population genetics and vector competence of vector species is critical to effectively preventing and controlling vector-borne diseases. The aim of this study was to examine the genetic structure and vector competence for dengue virus type 2 (DENV-2) of Ae. albopictus populations across China and their relationship.Methods: From July to September in 2019, Ae. albopictus eggs were collected by using ovitraps in 8 localities across China and reared to adults in laboratory. The mitochondrial gene cytochrome c oxidase subunit 1 (cox1) were used to examine the patterns of genetic diversity and population structure among native Ae. albopictus populations. The vector competence was detected by quantitative analysis of DENV-2 virus titer in mosquito tissues (midguts, heads and salivary glands) through qRT-PCR. The correlation between population genetic indices and DENV-2 loads in the mosquitoes’ tissues was also examined.Results: A total of 20 haplotypes of mtDNA cytochrome c oxidase subunit 1 (cox1) were identified in the 120 specimens from the eight tested populations. The dominate haplotype H01 was detected in seven geographic populations of mainland China. Genetic parameters such as haplotype diversity (Hd), nucleotide diversity (π), and fixation index (FST) revealed the population diversity decreasing from south to north, and low population genetic differentiation. STRUCTURE analysis indicated that Ae. albopictus populations in southern China were clustered. In addition, The Mantel test indicated a positive correlation between genetic distance and geographical distance (R2 = 0.364, P = 0.003). We observed no correlation between population genetic indices of cox1 in Ae. albopictus populations and DENV-2 virus loads. However, the southern populations had the low DENV-2 virus loads generally.Conclusion: Conventional genetic markers such as cox1 may not reflect genetic differences in mosquitoes’ vector competence in different regions. The fact of lower DENV-2 loads in southern populations may be associated with the stable immunity system established in mosquitoes due to the long-term prevalence of dengue disease in these areas. The genetic structure and vector competence of Ae. albopictus populations in this study may have implications for understanding the epidemiology, prevention and control of vector-borne diseases.
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