17 research outputs found
Enhanced Zika virus susceptibility of globally invasive Aedes aegypti populations
The drivers and patterns of zoonotic virus emergence in the human population are poorly understood. The mosquito Aedes aegypti is a major arbovirus vector native to Africa that invaded most of the worldâs tropical belt over the past four centuries, after the evolution of a âdomesticâ form that specialized in biting humans and breeding in water storage containers. Here, we show that human specialization and subsequent spread of A. aegypti out of Africa were accompanied by an increase in its intrinsic ability to acquire and transmit the emerging human pathogen Zika virus. Thus, the recent evolution and global expansion of A. aegypti promoted arbovirus emergence not solely through increased vectorâhost contact but also as a result of enhanced vector susceptibility
Potentiel du moustique Aedes malayensis comme vecteur dâarbovirus en Asie du Sud-Est
Many emerging arthropod-borne viruses (arboviruses) such as dengue virus (DENV) and yellow fever virus (YFV) originated in sylvatic cycles and have emerged among humans through spillover transmission by mosquito species that âbridgeâ sylvatic and human transmission cycles. These bridge vectors can also mediate âspillbackâ transmission of arboviruses from humans into novel sylvatic cycles. This PhD focused on Aedes malayensis, a mosquito species widely distributed in South East Asia, to assess its potential as an arbovirus vector. We identified Ae. malayensis for the first time in Laos during mosquito surveys conducted in a forested area of the Nakai Nam Theun National Protected Area (NNT NPA). Using field-based human-baited traps, we found that Ae. malayensis engaged in human-biting behavior and therefore could act as bridge vector in the NNT NPA. In laboratory conditions, this sylvatic population of Ae. malayensis displayed a relatively low vector competence for DENV and YFV and a lack of detectable attraction to human odor. However, vector competence assays and a human-baited trap survey showed that a peridomestic Ae. malayensis population in Singapore was competent for YFV and engaged in contact with humans. Overall, this PhD work highlighted that ancillary vectors should not be overlooked to fully assess the risk of arbovirus emergence.De nombreux virus transmis par les arthropodes (arbovirus), tels que ceux de la dengue (DENV) et de la fiĂšvre jaune (YFV), circulaient Ă lâorigine dans des cycles selvatiques et ont Ă©mergĂ© chez lâHomme via des moustiques « bridge vectors » qui connectent les cycles de transmission selvatiques et humains. Ces « bridge vectors » peuvent aussi par transfert inverse Ă©tablir de nouveaux cycles selvatiques. Cette thĂšse a Ă©valuĂ© le potentiel de vecteur dâarbovirus dâun moustique rĂ©pandu en Asie du sud-est, Aedes malayensis. Nous avons identifiĂ© Ae. malayensis pour la premiĂšre fois au Laos lors de captures de moustiques dans une forĂȘt de la rĂ©serve de Nakai Nam Theun. En utilisant des piĂšges Ă appĂąts humains sur le terrain, nous avons observĂ© quâAe. malayensis pouvait piquer lâHomme et donc potentiellement agir comme « bridge vector ». En laboratoire, cette population selvatique dâAe. malayensis a montrĂ© une faible compĂ©tence vectorielle relative pour DENV et YFV, et une absence dâattraction dĂ©tectable pour lâodeur humaine. Cependant, des tests de compĂ©tence vectorielle et de piĂšges Ă appĂąts humains ont rĂ©vĂ©lĂ© quâune population pĂ©ri-domestique dâAe. malayensis Ă Singapour Ă©tait compĂ©tente pour YFV et entrait en contact avec lâHomme. Au final, ce travail de doctorat a soulignĂ© lâimportance de ne pas nĂ©gliger les vecteurs secondaires dans lâĂ©valuation du risque dâĂ©mergence des arbovirus
New records and updated checklist of mosquitoes (Diptera: Culicidae) from Lao People's Democratic Republic, with special emphasis on adult and larval surveillance in Khammuane Province
International audienceA list of mosquitoes from the Nakai Nam Theun National Protected Area along the Nam Theun, Nam Mon, Nam Noy, and Nam On rivers, Nakai District, Khammuane Province, Lao People's Democratic Republic (Lao PDR) is presented. Fifty-four mosquito taxa were identified, including 15 new records in the Lao PDR. A fragment of the mtDNA cytochrome c oxidase subunit I (COI) gene, barcode region, was generated for 34 specimens, and together with four specimens already published, it represented 23 species in eight genera. In addition, an updated checklist of 170 mosquito taxa from Lao PDR is provided based on field collections from Khammuane Province, the literature, and specimens deposited in the Smithsonian Institution, National Museum of Natural History (SI-NMNH), Washington, DC, U.S.A. This paper provides additional information about the biodiversity of mosquito fauna in Lao PDR
Low Transmission of Chikungunya Virus by <i>Aedes aegypti</i> from Vientiane Capital, Lao PDR
In 2012â2013, chikungunya virus (CHIKV) was the cause of a major outbreak in the southern part of Lao Peopleâs Democratic Republic (Lao PDR). Since then, only a few imported cases, with isolates belonging to different lineages, were recorded between 2014 and 2020 in Vientiane capital and few autochthonous cases of ECSA-IOL lineage were detected in the south of the country in 2020. The CHIKV epidemiological profile contrasts with the continuous and intensive circulation of dengue virus in the country, especially in Vientiane capital. The studyâs aim was to investigate the ability of the local field-derived Aedes aegypti population from Vientiane capital to transmit the Asian and ECSA-IOL lineages of CHIKV. Our results revealed that, for both CHIKV lineages, infection rates were low and dissemination rates were high. The transmission rates and efficiencies evidenced a low vector competence for the CHIKV tested. Although this population of Ae. aegypti showed a relatively modest vector competence for these two CHIKV lineages, several other factors could influence arbovirus emergence such as the longevity and density of female mosquitoes. Due to the active circulation of CHIKV in Southeast Asia, investigations on these factors should be done to prevent the risk of CHIKV emergence and spread in Lao PDR and neighboring countries
Risk of arbovirus emergence via bridge vectors: case study of the sylvatic mosquito Aedes malayensis in the Nakai district, Laos
International audienceMany emerging arboviruses of global public health importance, such as dengue virus (DENV) and yellow fever virus (YFV), originated in sylvatic transmission cycles involving wild animals and forest-dwelling mosquitoes. Arbovirus emergence in the human population typically results from spillover transmission via bridge vectors, which are competent mosquitoes feeding on both humans and wild animals. Another related, but less studied concern, is the risk of 'spillback' transmission from humans into novel sylvatic cycles. We colonized a sylvatic population of Aedes malayensis from a forested area of the Nakai district in Laos to evaluate its potential as an arbovirus bridge vector. We found that this Ae. malayensis population was overall less competent for DENV and YFV than an urban population of Aedes aegypti. Olfactometer experiments showed that our Ae. malayensis colony did not display any detectable attraction to human scent in laboratory conditions. The relatively modest vector competence for DENV and YFV, combined with a lack of detectable attraction to human odor, indicate a low potential for this sylvatic Ae. malayensis population to act as an arbovirus bridge vector. However, we caution that opportunistic blood feeding on humans by sylvatic Ae. malayensis may occasionally contribute to bridge sylvatic and human transmission cycles
A peridomestic Aedes malayensis population in Singapore can transmit yellow fever virus
International audienceThe case-fatality rate of yellow fever virus (YFV) is one of the highest among arthropod-borne viruses (arboviruses). Although historically, the Asia-Pacific region has remained free of YFV, the risk of introduction has never been higher due to the increasing influx of people from endemic regions and the recent outbreaks in Africa and South America. Singapore is a global hub for trade and tourism and therefore at high risk for YFV introduction. Effective control of the main domestic mosquito vector Aedes aegypti in Singapore has failed to prevent re-emergence of dengue, chikungunya and Zika viruses in the last two decades, raising suspicions that peridomestic mosquito species untargeted by domestic vector control measures may contribute to arbovirus transmission. Here, we provide empirical evidence that the peridomestic mosquito Aedes malayensis found in Singapore can transmit YFV. Our laboratory mosquito colony recently derived from wild Ae. malayensis in Singapore was experimentally competent for YFV to a similar level as Ae. aegypti controls. In addition, we captured Ae. malayensis females in one human-baited trap during three days of collection, providing preliminary evidence that host-vector contact may occur in field conditions. Finally, we detected Ae. malayensis eggs in traps deployed in high-rise building areas of Singapore. We conclude that Ae. malayensis is a competent vector of YFV and re-emphasize that vector control methods should be extended to target peridomestic vector species
Cell-Fusing Agent Virus Reduces Arbovirus Dissemination in Aedes aegypti Mosquitoes In Vivo.
International audienceAedes aegypti mosquitoes are the main vectors of arthropod-borne viruses (arboviruses) of public health significance, such as the flaviviruses dengue virus (DENV) and Zika virus (ZIKV). Mosquitoes are also the natural hosts of a wide range of viruses that are insect specific, raising the question of their influence on arbovirus transmission in nature. Cell-fusing agent virus (CFAV) was the first described insect-specific flavivirus, initially discovered in an A. aegypti cell line and subsequently detected in natural A. aegypti populations. It was recently shown that DENV and the CFAV strain isolated from the A. aegypti cell line have mutually beneficial interactions in mosquito cells in culture. However, whether natural strains of CFAV and DENV interact in live mosquitoes is unknown. Using a wild-type CFAV isolate recently derived from Thai A. aegypti mosquitoes, we found that CFAV negatively interferes with both DENV type 1 and ZIKV in vitro and in vivo. For both arboviruses, prior infection by CFAV reduced the dissemination titer in mosquito head tissues. Our results indicate that the interactions observed between arboviruses and the CFAV strain derived from the cell line might not be a relevant model of the viral interference that we observed in vivo. Overall, our study supports the hypothesis that insect-specific flaviviruses may contribute to reduce the transmission of human-pathogenic flaviviruses. IMPORTANCE The mosquito Aedes aegypti carries several arthropod-borne viruses (arboviruses) that are pathogenic to humans, including dengue and Zika viruses. Interestingly , A. aegypti is also naturally infected with insect-only viruses, such as cell-fusing agent virus. Although interactions between cell-fusing agent virus and den-gue virus have been documented in mosquito cells in culture, whether wild strains of cell-fusing agent virus interfere with arbovirus transmission by live mosquitoes was unknown. We used an experimental approach to demonstrate that cell-fusing agent virus infection reduces the propagation of dengue and Zika viruses in A. ae-gypti mosquitoes. These results support the idea that insect-only viruses in nature can modulate the ability of mosquitoes to carry arboviruses of medical significance and that they could possibly be manipulated to reduce arbovirus transmission
Population genetics of Aedes albopictus (Diptera: Culicidae) in its native range in Lao Peopleâs Democratic Republic
International audienceBackgroundThe Asian tiger mosquito, Aedes ( Stegomyia ) albopictus (Skuse) is an important worldwide invasive species and can be a locally important vector of chikungunya, dengue and, potentially, Zika. This species is native to Southeast Asia where populations thrive in both temperate and tropical climates. A better understanding of the population structure of Ae. albopictus in Lao PDR is very important in order to support the implementation of strategies for diseases prevention and vector control. In the present study, we investigated the genetic variability of Ae. albopictus across a north-south transect in Lao PDR.MethodsWe used variability in a 1337-bp fragment of the mitochondrial cytochrome c oxidase subunit 1 gene ( cox 1), to assess the population structure of Ae. albopictus in Lao PDR. For context, we also examined variability at the same genetic locus in samples of Ae. albopictus from Thailand, China, Taiwan, Japan, Singapore, Italy and the USA.ResultsWe observed very high levels of genetic polymorphism with 46 novel haplotypes in Ae. albopictus from 9 localities in Lao PDR and Thailand populations. Significant differences were observed between the Luangnamtha population and other locations in Lao PDR. However, we found no evidence of isolation by distance. There was overall little genetic structure indicating ongoing and frequent gene flow among populations or a recent population expansion. Indeed, the neutrality test supported population expansion in Laotian Ae. albopictus and mismatch distribution analyses showed a lack of low frequency alleles, a pattern often seen in bottlenecked populations. When samples from Lao PDR were analyzed together with samples from Thailand, China, Taiwan, Japan, Singapore, Italy and the USA, phylogenetic network and Bayesian cluster analysis showed that most populations from tropical/subtropical regions are more genetically related to each other, than populations from temperate regions. Similarly, most populations from temperate regions are more genetically related to each other, than those from tropical/subtropical regions.ConclusionsAedes albopictus in Lao PDR are genetically related to populations from tropical/subtropical regions (i.e. Thailand, Singapore, and California and Texas in the USA). The extensive gene flow among locations in Lao PDR indicates that local control is undermined by repeated introductions from untreated sites
Recent African strains of Zika virus display higher transmissibility and fetal pathogenicity than Asian strains
The global emergence of Zika virus (ZIKV) revealed the unprecedented ability for a mosquito-borne virus to cause congenital birth defects. A puzzling aspect of ZIKV emergence is that all human outbreaks and birth defects to date have been exclusively associated with the Asian ZIKV lineage, despite a growing body of laboratory evidence pointing towards higher transmissibility and pathogenicity of the African ZIKV lineage. Whether this apparent paradox reflects the use of relatively old African ZIKV strains in most laboratory studies is unclear. Here, we experimentally compare seven low-passage ZIKV strains representing the recently circulating viral genetic diversity. We find that recent African ZIKV strains display higher transmissibility in mosquitoes and higher lethality in both adult and fetal mice than their Asian counterparts. We emphasize the high epidemic potential of African ZIKV strains and suggest that they could more easily go unnoticed by public health surveillance systems than Asian strains due to their propensity to cause fetal loss rather than birth defects