Larval development of Aedes aegypti and Aedes albopictus in peri-urban brackish water and its implications for transmission of arboviral diseases.
ABSTRACT: Aedes aegypti (Linnaeus) and Aedes albopictus Skuse mosquitoes transmit serious human arboviral diseases including yellow fever, dengue and chikungunya in many tropical and sub-tropical countries. Females of the two species have adapted to undergo preimaginal development in natural or artificial collections of freshwater near human habitations and feed on human blood. While there is an effective vaccine against yellow fever, the control of dengue and chikungunya is mainly dependent on reducing freshwater preimaginal development habitats of the two vectors. We show here that Ae. aegypti and Ae. albopictus lay eggs and their larvae survive to emerge as adults in brackish water (water with <0.5 ppt or parts per thousand, 0.5-30 ppt and >30 ppt salt are termed fresh, brackish and saline respectively). Brackish water with salinity of 2 to 15 ppt in discarded plastic and glass containers, abandoned fishing boats and unused wells in coastal peri-urban environment were found to contain Ae. aegypti and Ae. albopictus larvae. Relatively high incidence of dengue in Jaffna city, Sri Lanka was observed in the vicinity of brackish water habitats containing Ae. aegypti larvae. These observations raise the possibility that brackish water-adapted Ae. aegypti and Ae. albopictus may play a hitherto unrecognized role in transmitting dengue, chikungunya and yellow fever in coastal urban areas. National and international health authorities therefore need to take the findings into consideration and extend their vector control efforts, which are presently focused on urban freshwater habitats, to include brackish water larval development habitats.
Project description:The mainly fresh water arboviral vector Aedes aegypti L. (Diptera: Culicidae) can also undergo pre-imaginal development in brackish water of up to 15 ppt (parts per thousand) salt in coastal areas. We investigated differences in salinity tolerance, egg laying preference, egg hatching and larval development times and resistance to common insecticides in Ae. aegypti collected from brackish and fresh water habitats in Jaffna, Sri Lanka. Brackish water-derived Ae. aegypti were more tolerant of salinity than fresh water-derived Ae. aegypti and this difference was only partly reduced after their transfer to fresh water for up to five generations. Brackish water-derived Ae. aegypti did not significantly discriminate between 10 ppt salt brackish water and fresh water for oviposition, while fresh water-derived Ae. aegypti preferred fresh water. The hatching of eggs from both brackish and fresh water-derived Ae. aegypti was less efficient and the time taken for larvae to develop into pupae was prolonged in 10 ppt salt brackish water. Ae. aegypti isolated from coastal brackish water were less resistant to the organophosphate insecticide malathion than inland fresh water Ae. aegypti. Brackish and fresh water-derived Ae. aegypti however were able to mate and produce viable offspring in the laboratory. The results suggest that development in brackish water is characterised by pertinent biological changes, and that there is restricted genetic exchange between coastal brackish and inland fresh water Ae. aegypti isolates from sites 5 km apart. The findings highlight the need for monitoring Ae. aegypti developing in coastal brackish waters and extending vector control measures to their habitats.
Project description:Dengue fever, chikungunya, and Zika are diseases caused by viruses transmitted by Aedes aegypti and Aedes albopictus. In Brazil, the number of human infections is high, but few studies are performed in mosquito vectors. This study aimed to investigate the presence of Zika, Dengue and Chikungunya viruses in Ae. aegypti and Ae. albopictus from the municipalities of Alto Alegre, Caxias, Codó, and São Mateus do Maranhão, located in the state of Maranhão, Northeast Brazil. The mosquitoes were collected with a mechanical aspirator, identified, triturated, and then submitted to RNA extraction and RT-qPCR. The positive samples were confirmed by virus isolation and genome sequencing. Three hundred and forty-eight Ae. aegypti (176 males and 172 females) and 12 Ae. albopictus (eight males and four females) were collected and tested. Ae. aegypti was the only vector positive in two municipalities-Codó, with detection of Chikungunya virus (CHIKV) belonging to the East-Central-South African genotype, and in Caxias, with detection of Dengue virus (DENV)-2 belonging to the Asian/American genotype. The detection of CHIKV and DENV-2 is evidence that those viruses are maintained in arthropod vectors, and shows the epidemiological risk in the area for chikungunya cases and a possible increase of severe dengue cases, associated with the occurrence of dengue hemorrhagic fever.
Project description:Aedes aegypti, the principle global vector of arboviral diseases, has been widely regarded to only lay eggs and undergo preimaginal development in fresh water collections. Recent observations however show that it has adapted to develop in anthropogenic brackish water habitats of up to 50% sea water in coastal areas in different continents. This adaptation is characterised by greater salinity tolerance in adult oviposition preference, larvae and changes in sizes of anal papillae. The physiological basis for salinity tolerance in either Ae. aegypti or any of the known salinity-tolerant species of Anopheles malaria vectors is not established. To address this knowledge gap which is of fundamental biological interest and important for control of major diseases we performed RNAseq analysis of gut, anal papillae, and rest of the carcass of Ae. aegypti collected in the field from brackish water (BW) and fresh water habitats (FW) and then maintained as laboratory colonies in BW and FW respectively. We also examined the cuticle structure of larvae, pupae and adult BW and FW Ae. aegypti by microscopy and performed proteomic analysis of the shed cuticles of fourth instar larvae (L4) when they transformed into pupae. The results show that major changes in cuticle structure and composition characterize, and may be the principal factor that permits, the adaptation of Ae. aegypti to brackish water.
Project description:Previous studies have shown that the negative effects of density of Ae. albopictus on Ae. aegypti exceed those of Ae. aegypti on Ae. albopictus for population growth, adult size, survivorship, and developmental rate. This competitive superiority has been invoked to explain the displacement of Ae. aegypti by Ae. albopictus in the southeastern USA. In Brazil, these species coexist in many vegetated suburban and rural areas. We investigated a related, but less-well-studied question: do effects of Ae. albopictus on Ae. aegypti larval development and survival occur under field conditions at realistic densities across multiple seasons in Brazil? We conducted additive competition experiments in a vegetated area of Rio de Janeiro where these species coexist. We tested the hypothesis that Ae. aegypti (the focal species, at a fixed density) suffers negative effects on development and survivorship across a gradient of increasing densities of Ae. albopictus (the associate species) in three seasons. The results showed statistically significant effects of both season and larval density on Ae. aegypti survivorship, and significant effects of season on development rate, with no significant season-density interactions. Densities of Aedes larvae in these habitats differed among seasons by a factor of up to 7x. Overall, Spring was the most favorable season for Ae. aegypti survivorship and development. Results showed that under natural conditions the negative competitive effects of Ae. albopictus on Ae. aegypti were expressed primarily as lower survivorship. Coexistence between Ae. aegypti and Ae. albopictus in vegetated areas is likely affected by seasonal environmental differences, such as detrital resource levels or egg desiccation, which can influence competition between these species. Interactions between these Aedes are important in Brazil, where both species are well established and widely distributed and vector dengue, Zika and chikungunya viruses.
Project description:Aedes aegypti and Aedes albopictus develop in the same aquatic sites where they encounter microorganisms that influence their life history and capacity to transmit human arboviruses. Some bacteria such as Wolbachia are currently being considered for the control of Dengue, Chikungunya and Zika. Yet little is known about the dynamics and diversity of Aedes-associated bacteria, including larval habitat features that shape their tempo-spatial distribution. We applied large-scale 16S rRNA amplicon sequencing to 960 adults and larvae of both Ae. aegypti and Ae. albopictus mosquitoes from 59 sampling sites widely distributed across nine provinces of Panama. We find both species share a limited, yet highly variable core microbiota, reflecting high stochasticity within their oviposition habitats. Despite sharing a large proportion of microbiota, Ae. aegypti harbours higher bacterial diversity than Ae. albopictus, primarily due to rarer bacterial groups at the larval stage. We find significant differences between the bacterial communities of larvae and adult mosquitoes, and among samples from metal and ceramic containers. However, we find little support for geography, water temperature and pH as predictors of bacterial associates. We report a low incidence of natural Wolbachia infection for both Aedes and its geographical distribution. This baseline information provides a foundation for studies on the functions and interactions of Aedes-associated bacteria with consequences for bio-control within Panama.
Project description:Background:Refillable water containers are commonly used in rural areas of Lao PDR, and they act as Aedes mosquito breeding sites. Aedes aegypti and Ae. albopictus mosquitos are transmission vectors for the dengue virus, which causes dengue fever. Methods:Two isolated rural villages in the central part of Lao PDR were selected as study sites. In the intervention village, domestic water containers were continuously treated with a long-lasting matrix release formulation, containing pyriproxyfen, named SumiLarv®2MR. In the control village, entomological activity was monitored, but no intervention was performed. Baseline data were collected in both villages during the late rainy season (October 2017) then distributed SumiLarv®2MR disks in intervention village. This data was compared with data collected during the intervention periods in the dry season (February 2018), rainy season (July 2018 and 2019), and late rainy season (September 2018) in the region. Results:Compared with the baseline data (20.24%), the percentage of water containers infested with Ae. aegypti larvae was significantly decreased in the treated village, especially in the rainy seasons in July 2018 (4.11%; P < 0.001) and July 2019 (2.46%; P < 0.001), while the percentage of water containers infested with Ae. albopictus larvae did not decrease significantly in prevalence. No reduction in the frequency of Aedes species was seen in the control village. The Ae. albopictus liked to breed in small habitats (the median water volume of its habitats was 5?L and 10?L in the control and treated village, respectively, while the equivalent values for Ae. aegypti were 30?L and 50?L, respectively). Conclusion:The treatment of refillable water storage containers in a rural village with SumiLarv®2MR disks led to significant reductions in the Ae. aegypti population. However, the Ae. albopictus population did not decrease in either the control or treated village. This discrepancy was due to differences in habitat-seeking behaviors and preferred breeding sites such as types of water, water container, and water volume, then led to the differences in results of mosquito prevalence after SumiLarv®2MR disk treatments. The SumiLarv®2MR disk treatment was proven to be effective against the primary dengue-virus vector mosquitoes, Ae. aegypti.
Project description:The rapid expansion of Zika virus (ZIKV), following the recent outbreaks of Chikungunya virus, overwhelmed the public health infrastructure in many countries and alarmed many in the scientific community. Aedes aegypti (L.) (Diptera: Culicidae) and Aedes albopictus (Skuse) (Diptera: Culicidae) have previously been incriminated as the vectors of these pathogens in addition to dengue virus. In our study, we challenged low generation Ae. aegypti (Chiapas, Mexico) and Ae. albopictus (North Carolina, Mississippi), with three strains of ZIKV, Puerto Rico (GenBank: KU501215), Honduras (GenBank: KX694534), and Miami (GenBank: MF988743). Following an oral challenge with 107.5 PFU/ml of the Puerto Rico strain, we observed high infection and dissemination rates in both species (95%). We report estimated transmission rates for both species (74 and 33%, for Ae. aegypti (L.) (Diptera: Culicidae) and Ae. albopictus (Skuse) (Diptera: Culicidae), respectively), and the presence of a probable salivary gland barrier in Ae. albopictus to Zika virus. Finally, we calculated vectorial capacity for both species and found that Ae. albopictus had a slightly lower vectorial capacity when compared with Ae. aegypti.Second Language Abstract: La rápida expansión del virus Zika, poco después de las epidemias de chikungunya, rebaso la infraestructura de salud pública en muchos países y sorprendió a muchos en la comunidad científica. Notablemente, Aedes aegypti y Aedes albopictus transmiten estos patógenos además del virus del dengue. En este estudio se expusieron con tres cepas americanas de virus Zika a grupos de Aedes aegypti y Aedes albopictus de generación reciente. Encontramos altos porcentajes de infección y diseminación en ambas especies (95%). Se reporta, la transmisión viral en ambas especies (74 y 33%, para Aedes aegypti and Aedes albopictus, respectivamente) y una probable barrera a nivel de glándulas salivarías. Finalmente, calculamos la capacidad vectorial para ambas especies.
Project description:BACKGROUND:The presence of the recently introduced primary dengue virus vector mosquito Aedes aegypti in Nepal, in association with the likely indigenous secondary vector Aedes albopictus, raises public health concerns. Chikungunya fever cases have also been reported in Nepal, and the virus causing this disease is also transmitted by these mosquito species. Here we report the results of a study on the risk factors for the presence of chikungunya and dengue virus vectors, their elevational ceiling of distribution, and climatic determinants of their abundance in central Nepal. METHODOLOGY/PRINCIPAL FINDINGS:We collected immature stages of mosquitoes during six monthly cross-sectional surveys covering six administrative districts along an altitudinal transect in central Nepal that extended from Birgunj (80 m above sea level [asl]) to Dhunche (highest altitude sampled: 2,100 m asl). The dengue vectors Ae. aegypti and Ae. albopictus were commonly found up to 1,350 m asl in Kathmandu valley and were present but rarely found from 1,750 to 2,100 m asl in Dhunche. The lymphatic filariasis vector Culex quinquefasciatus was commonly found throughout the study transect. Physiographic region, month of collection, collection station and container type were significant predictors of the occurrence and co-occurrence of Ae. aegypti and Ae. albopictus. The climatic variables rainfall, temperature, and relative humidity were significant predictors of chikungunya and dengue virus vectors abundance. CONCLUSIONS/SIGNIFICANCE:We conclude that chikungunya and dengue virus vectors have already established their populations up to the High Mountain region of Nepal and that this may be attributed to the environmental and climate change that has been observed over the decades in Nepal. The rapid expansion of the distribution of these important disease vectors in the High Mountain region, previously considered to be non-endemic for dengue and chikungunya fever, calls for urgent actions to protect the health of local people and tourists travelling in the central Himalayas.
Project description:Temperature-food interactions in the larval environment can affect life history and population growth of container mosquitoes Aedes aegypti (L.) and Aedes albopictus Skuse, the primary vectors of chikungunya and dengue viruses. We used Ae. aegypti, Ae. albopictus, and dengue-1 virus (DENV-1) from Florida to investigate whether larval rearing temperature can alter the effects of larval food levels on Ae. aegypti and Ae. albopictus life history and DENV-1 infection and vertical transmission. Although we found no effect of larval treatments on survivorship to adulthood, DENV-1 titer, or DENV-1 vertical transmission, rates of vertical transmission up to 16-24% were observed in Ae. albopictus and Ae. aegypti, which may contribute to maintenance of this virus in nature. Larval treatments had no effect on number of progeny and DENV-1 infection in Ae. aegypti, but the interaction between temperature and food affected number of progeny and DENV-1 infection of the female Ae. albopictus parent. The cooler temperature (24°C) yielded the most progeny and this effect was accentuated by high food relative to the other conditions. Low and high food led to the highest (?90%) and lowest (?65%) parental infection at the cooler temperature, respectively, whereas intermediate infection rates (?75-80%) were observed for all food conditions at the elevated temperature. These results suggest that temperature and food availability have minimal influence on rate of vertical transmission and a stronger influence on adults of Ae. albopictus than of Ae. aegypti, which could have consequences for dengue virus epidemiology.
Project description:We assessed risk factors for vectors of dengue and chikungunya viruses near a new hydroelectric project, Nam Theun 2, in Laos. Immature stages of Aedes aegypti were found only in sites within 40 km of the urban provincial capital, but Aedes albopictus was found throughout. Aedes aegypti pupae were most common in water storage jars (odds ratio [OR] = 4.72) and tires (OR = 2.99), and Ae. albopictus pupae were associated with tires in 2009 (OR = 10.87) and drums, tires, and jars in 2010 (drums OR = 3.05; tires OR = 3.45, jars OR = 6.59). Compared with water storage vessels, containers used for hygiene, cooking, and drinking were 80% less likely to harbor Ae. albopictus pupae in 2010 (OR = 0.20), and discarded waste was associated with a 3.64 increased odds of infestation. Vector control efforts should focus on source reduction of water storage containers, particularly concrete jars and tires.