First dengue virus detection in Aedes albopictus from Delhi, India: its breeding ecology and role in dengue transmission

Objective To report dengue virus and its disease transmission in Aedes albopictus in the National Capital Territory of Delhi, India. Methods Monthly Aedes surveys were carried out in 126 urban localities of Delhi in 2008 and 2009. Pools of all three species of Aedes mosquitoes were tested for Dengue virus (DENV) using an antigen‐capture enzyme‐linked immunosorbent assay. Results Aedes aegypti was the most prevalent species, breeding throughout the year. Aedes albopictus was found in 9.52% of surveyed localities including the central urban part of Delhi, in March and from August to October. Aedes albopictus and Aedes vittatus are adapting to breed in manmade containers in the urban areas of Delhi in addition to their natural habitats of bamboo bushes and rock pits. Of the 229 pools of Ae. aegypti and 34 pools of Ae. albopictus tested, 10.5% and 11.76% were positive for dengue virus, respectively. No dengue virus infection was recorded in Ae. vittatus. Conclusion This is the first report of dengue virus in Ae. albopictus from north India. Because DENV was detected in Ae. albopictus, which adapted to manmade containers, both its spread and transmission dynamics should be checked.     

First Report of Wenzhou sobemo-like virus 4 in Aedes albopictus (Diptera: Culicidae) in Latin America

Insect-specific viruses (ISVs) are viruses that replicate exclusively in arthropod cells. Many ISVs have been studied in mosquitoes as many of them act as vectors for human etiological agents, such as arboviruses. Aedes (Stegomyia) albopictus is an important potential vector of several arboviruses in Brazil, such as dengue (DENV), Zika (ZIKV) and chikungunya (CHIKV). The development of next-generation sequencing metagenomics has enabled the discovery and characterization of new ISVs. Ae. albopictus eggs were collected using oviposition traps placed in two urban parks in the city of São Paulo, Brazil. The Aedes albopictus females were divided into pools and the genetic material was extracted and processed for sequencing by metagenomics. Complete genomes of ISV Wenzhou sobemo-like virus 4 (WSLV4) were obtained in three of the four pools tested. This is the first detection of ISV WSLV4 in Ae. albopictus females in Latin America. Further studies on ISVs in Ae. albopictus are needed to better understand the role of this species in the dynamics of arbovirus transmission in the Americas.     

Distribution of Mosquito Larvae on Kosrae Island,Kosrae State,the Federated States of Micronesia

Surveys of mosquito larvae were carried out in six areas of Kosrae Island, Kosrae State, the Federated States of Micronesia in December 2009 and June 2012. A total of 962 larvae of six species were collected from 106 natural and artificial habitats. They were identified as Aedes aegypti, Ae. albopictus, Ae. marshallensis, Culex quinquefasciatus, Cx. annulirostris, and Cx. kusaiensis. This is the first report from Kosrae Island for three of these species—Ae. marshallensis, Cx. quinquefasciatus, and Cx. annulirostris. The most abundant species was Ae. albopictus, followed by Ae. marshallensis, and these two species were found in all areas. Relatively large numbers of Cx. quinquefasciatus and Cx. kusaiensis were found in five areas. Fewer Cx. annulirostris were found, and only in three areas. Aedes aegypti larvae were collected from a single habitat at Tafunsak in 2009. To prevent the outbreak of dengue fever, environmental management should focus on the destruction, alteration, disposal and recycling of containers that produce larger numbers of adult Aedes mosquitoes.     

First record of Ae. albopictus (Skuse 1894), in Central African Republic

Methods Mosquito aquatic stages were collected in domestic and peri‐domestic areas, and epidemic risk indexes (Breteau, Container) were calculated for each prospected location. Adult female mosquitoes were captured by human landing catches, while larvae were sampled by inspecting artificial and natural breeding sites in randomly selected premises. Results Seventy‐eight adults Aedes albopictus were collected in Bangui and Bayanga. Mosquito biting rate and abundance were, respectively, 0.33–1.70 bites/human/hour and 14.6% in Bangui and 0.04–0.16 and 0.4% in Bayanga. Larval sampling revealed a large diversity of water container harbouring the species in Bangui, Bayanga, Nola and Salo including unused containers, old tires, vehicle carcasses, buckets, barrels and stem of bamboo. The epidemic risk indices were erratic according to the location, ranging between 1.5–27.6 for Breteau and 1.3–47.1 for Container. Conclusion This is the first record of Ae. albopictus in two bioclimatic zones of CAR This observation emphasizes the need to further investigate its potential impact on dengue and chikungunya viruses transmission regarding their recent emergences in Africa (Côte d’Ivoire, Senegal, Mali, Somalia, Gabon, Cape Verde Islands).     

Evaluation of Aedes aegypti,Aedes albopictus,and Culex quinquefasciatus Mosquitoes Competence to Oropouche virus Infection

The emergence of new human viral pathogens and re-emergence of several diseases are of particular concern in the last decades. Oropouche orthobunyavirus (OROV) is an arbovirus endemic to South and Central America tropical regions, responsible to several epidemic events in the last decades. There is little information regarding the ability of OROV to be transmitted by urban/peri-urban mosquitoes, which has limited the predictability of the emergence of permanent urban transmission cycles. Here, we evaluated the ability of OROV to infect, replicate, and be transmitted by three anthropophilic and urban species of mosquitoes, Aedes aegypti, Aedes albopictus, and Culex quinquefasciatus. We show that OROV is able to infect and efficiently replicate when systemically injected in all three species tested, but not when orally ingested. Moreover, we find that, once OROV replication has occurred in the mosquito body, all three species were able to transmit the virus to immunocompromised mice during blood feeding. These data provide evidence that OROV is restricted by the midgut barrier of three major urban mosquito species, but, if this restriction is overcome, could be efficiently transmitted to vertebrate hosts. This poses a great risk for the emergence of permanent urban cycles and geographic expansion of OROV to other continents.     

High-Throughput Method for Detection of Arbovirus Infection of Saliva in Mosquitoes Aedes aegypti and Ae. albopictus

Vector competence refers to the ability of a vector to acquire, maintain, and transmit a pathogen. Collecting mosquito saliva in medium-filled capillary tubes has become the standard for approximating arbovirus transmission. However, this method is time-consuming and labor-intensive. Here we compare the capillary tube method to an alternative high-throughput detection method the collection of saliva on paper cards saturated with honey, with (FTA card) and without (filter paper) reagents for the preservation of nucleic acid for Aedes aegypti and Aedes albopictus mosquitoes infected with two emerging genotypes of the chikungunya virus (CHIKV). Model results showed that the Asian genotype CHIKV dissemination in the harvested legs of both Ae. aegypti and Ae. albopictus increased the odds of females having a positive salivary infection and higher salivary viral titers, while for the IOL genotype the same effect was observed only for Ae. aegypti. Of the three tested detection methods, the FTA card was significantly more effective at detecting infected saliva of Ae. aegypti and Ae. albopictus females than the capillary tube and filter paper was as effective as the capillary tube for the Asian genotype. We did not find significant effects of the detection method in detecting higher viral titer for both Asian and IOL genotypes. Our results are discussed in light of the limitations of the different tested detection methods.     

Association of human immune response to Aedes aegypti salivary proteins with dengue disease severity

Dengue viruses (DENV; family Flaviviridae, genus Flavivirus) are transmitted by Aedes aegypti mosquitoes and can cause dengue fever (DF), a relatively benign disease, or more severe dengue haemorrhagic fever (DHF). Arthropod saliva contains proteins delivered into the bite wound that can modulate the host haemostatic and immune responses to facilitate the intake of a blood meal. The potential effects on DENV infection of previous exposure to Ae. aegypti salivary proteins have not been investigated. We collected Ae. aegypti saliva, concentrated the proteins and fractionated them by nondenaturing polyacrylamide gel electrophoresis (PAGE). By the use of immunoblots, we analysed reactivity with the mosquito salivary proteins (MSP) of sera from 96 Thai children diagnosed with secondary DENV infections leading either to DF or DHF, or with no DENV infection, and found that different proportions of each patient group had serum antibodies reactive to specific Ae. aegypti salivary proteins. Our results suggest that prior exposure to MSP might play a role in the outcome of DENV infection in humans.     

Dengue vector prevalence and virus infection in a rural area in south India

We conducted a 2-year (1997-1999) longitudinal, entomological and virological study in three dengue endemic villages in Vellore district, Tamil Nadu, to understand the dynamics of dengue transmission. Aedes aegypti (Linn.), Ae. albopictus (Skuse) and Ae. vittatus (Bigot) were the prevalent vector species. Aedes aegypti was breeding throughout the year with a Breteau index ranging from 9.05 to 45.49. Aedes albopictus and Ae. vittatus were prevalent mainly in the rainy season. Small water holding containers (cemented tanks/cisterns) were the perennial breeding source of Ae. aegypti, and its abundance was significantly higher in semi-urbanized central areas than the peripheral areas of the villages. From 271 pools (4016 specimens) of adult females, eight dengue virus (DENV) isolates were obtained of which seven were from Ae. aegypti and one from Ae. albopictus. This is the first report of DENV isolation from Ae. albopictus in rural India. Infection rates in the two species were comparable. However, due to higher and perennial prevalence, Ae. aegypti is considered as primary vector with Ae. albopictus playing a secondary role. Despite circulation of all four serotypes (DENV 1-4) detected mainly during the transmission season, the high anthropophilic index of the vectors and their abundance, no human dengue case was reported, suggesting silent dengue transmission.     

Abundant Aedes (Stegomyia) aegypti aegypti mosquitoes in the 2014 dengue outbreak area of Mozambique

In early 2014, dengue cases were reported from northern Mozambique, 30 years after the last outbreak. We identified potential dengue vector species in three northern towns, Pemba, Nampula and Nacala, and one southern town, Maputo, during the outbreak in April 2014. A major dengue vector species, Aedes (Stegomyia) aegypti, was found in all these towns. The dominant vector subspecies in the northern towns was Aedes aegypti aegypti, while Ae. aegypti formosus was dominant in Maputo. Considering the high proportion of Ae. aegypti aegypti and its high vector competence, the findings from this study suggest that Ae. aegypti aegypti was responsible for the outbreak in northern Mozambique.     

Short communication: first record of Aedes albopictus in Gabon, Central Africa

The Asian tiger mosquito Aedes albopictus is an important arbovirus vector. Originating in East Asia, the species has been introduced to the Americas, the Indo-Pacific and Australasian regions as well as Europe and Africa, mostly during the past 30 years and probably by transportation in used tires. We report Ae. albopictus for the first time from Gabon (Libreville). In addition, the yellow fever mosquito Ae. aegypti ssp. formosus and 16 other culicid species were detected throughout the city, four of which are also new records for Gabon.     

Chikungunya Virus Infection

Chikungunya virus (CHIKV) is an alphavirus transmitted by mosquitoes, mostly Aedes aegypti and Aedes albopictus. After half a century of focal outbreaks of acute febrile polyarthralgia in Africa and Asia, the disease unexpectedly spread in the past decade with large outbreaks in Africa and around the Indian Ocean and rare autochthonous transmission in temperate areas. This emergence brought new insights on its pathogenesis, notably the role of the A226V mutation that improved CHIKV fitness in Ae. albopictus and the possible CHIKV persistence in deep tissue sanctuaries for months after infection. Massive outbreaks also revealed new aspects of the acute stage: the high number of symptomatic cases, unexpected complications, mother-to-child transmission, and low lethality in debilitated patients. The follow-up of patients in epidemic areas has identified frequent, long-lasting, rheumatic disorders, including rare inflammatory joint destruction, and common chronic mood changes associated with quality-of-life impairment. Thus, the globalization of CHIKV exposes countries with Aedes mosquitoes both to brutal outbreaks of acute incapacitating episodes and endemic long-lasting disorders.     

Is routine dengue vector surveillance in central Brazil able to accurately monitor the Aedes aegypti population? Results from a pupal productivity survey

Objective To assess how well the Aedes aegypti infestation rapid survey, Levantamento Rapido de Indice para Aedes aegypti (LIRAa), is able to accurately estimate dengue vector densities and target the most important breeding sites in Goiania, Brazil. Methods In February 2009, a pupal productivity survey was conducted in 2 districts of the city of Goiania, central Brazil. The results were compared to those of LIRAas conducted in the same districts during the months before and after the pupal productivity survey. Results In the pupal productivity survey, 2 024 houses were surveyed and 2 969 water‐holding containers were inspected. Discarded small water containers most frequently contained immature Ae. aegypti. The most pupal‐productive containers were elevated water tanks, roof gutters and water holding roofs. Combined, these three containers accounted for <40% of all positive containers but produced >70% of all pupae. In the two districts where the pupal productivity survey was conducted, the house indices were 5.1 and 4.6 and the Breteau indices were 5.9 and 6.0. In contrast, the two LIRAs conducted in the same two districts resulted in an average house index of 1.5 and Breteau index of 2.5, with discarded items identified as the most frequently infested container type. Conclusion Both the LIRAa and the pupal productivity survey identified discarded items as being most frequently infested with immature stages of Ae. aegypti, but the pupal productivity survey showed that elevated containers produced the greatest proportion of Ae. aegypti pupae (a proxy measure of adult vector density) and that the values of the Stegomyia indices were substantially underestimated by LIRAa. Although both surveys differ considerably in terms of sampling method and manpower, in the case of this study the LIRAa did not accurately identify or target the containers that were the most important to adult mosquito production.     

Geographic Partitioning of Dengue Virus Transmission Risk in Florida

Dengue viruses (DENVs) cause the greatest public health burden globally among the arthropod-borne viruses. DENV transmission risk has also expanded from tropical to subtropical regions due to the increasing range of its principal mosquito vector, Aedes aegypti. Focal outbreaks of dengue fever (dengue) in the state of Florida (FL) in the USA have increased since 2009. However, little is known about the competence of Ae. aegypti populations across different regions of FL to transmit DENVs. To understand the effects of DENV genotype and serotype variations on vector susceptibility and transmission potential in FL, we orally infected a colony of Ae. aegypti (Orlando/ORL) with low passage or laboratory DENV-1 through -4. Low passage DENVs were more infectious to and had higher transmission potential by ORL mosquitoes. We used these same DENVs to examine natural Ae. aegypti populations to determine whether spatial distributions correlated with differential vector competence. Vector competence across all DENV serotypes was greater for mosquitoes from areas with the highest dengue incidence in south FL compared to north FL. Vector competence for low passage DENVs was significantly higher, revealing that transmission risk is influenced by virus/vector combinations. These data support a targeted mosquito-plus-pathogen screening approach to more accurately estimate DENV transmission risk.     

High susceptibility to Chikungunya virus of Aedes aegypti from the French West Indies and French Guiana

Objectives To estimate the vector competence of Aedes aegypti populations sampled from distinct anthropogenic environments in French Guiana, Guadeloupe and Martinique for the strain CHIKV 06.21. Methods F₁/F₂ females were orally infected at titres of 10⁶ and 10^7.5 pfu/ml in blood‐meals. Disseminated infection rates (DIR) of mosquitoes were estimated using indirect fluorescent antibody assay on heads’ squashes, 7 or 14 days post‐infection (pi). Results At a titre of 10^7.5 pfu/ml, DIR ranged from 88.9% to 100.0% and were not significantly different whether assessed at day 7 or 14 pi. At a titre of 10⁶ pfu/ml, DIR observed 7 days pi ranged from 37.6 to 62.0%. Conclusions Ae. aegypti from French Guiana and French West Indies are highly competent to transmit CHIKV. An evaluation of DIR 7 days rather than 14 days pi is adequate to estimate vector competence. The titre of 10⁶ pfu/ml allows us to distinguish Ae. aegypti populations originating from distinct environments (dense or diffuse housing) by their vector competence. This assessment is a prerequisite to better evaluate the potential risk of Chikungunya outbreaks once the virus is introduced from endemic regions.     

Brazilian Populations of Aedes aegypti Resistant to Pyriproxyfen Exhibit Lower Susceptibility to Infection with Zika Virus

Zika virus (ZIKV) infection has caused devastating consequences in Brazil as infections were associated with neurological complications in neonates. Aedes aegypti is the primary vector of ZIKV, and the evolution of insecticide resistance (IR) in this species can compromise control efforts. Although relative levels of phenotypic IR in mosquitoes can change considerably over time, its influence on vector competence for arboviruses is unclear. Pyriproxyfen (PPF)-resistant populations of Ae. aegypti were collected from five municipalities located in Northeast of Brazil, which demonstrated different resistance levels; low (Serrinha, Brumado), moderate (Juazeiro do Norte, Itabuna), and high (Quixadá). Experimental per os infection using ZIKV were performed with individuals from these populations and with an insecticide susceptible strain (Rockefeller) to determine their relative vector competence for ZIKV. Although all populations were competent to transmit ZIKV, mosquitoes derived from populations with moderate to high levels of IR exhibited similar or lower susceptibility to ZIKV infection than those from populations with low IR or the susceptible strain. These observations suggest an association between IR and arbovirus infection, which may be attributable to genetic hitchhiking. The use of PPF to control Brazilian Ae. aegypti may be associated with an indirect benefit of reduced susceptibility to infection, but no changes in disseminated infection and transmission of ZIKV among PPF-resistant phenotypes.     

Vector Competence of the Invasive Mosquito Species Aedes koreicus for Arboviruses and Interference with a Novel Insect Specific Virus

The global spread of invasive mosquito species increases arbovirus infections. In addition to the invasive species Aedes albopictus and Aedes japonicus, Aedes koreicus has spread within Central Europe. Extensive information on its vector competence is missing. Ae. koreicus from Germany were investigated for their vector competence for chikungunya virus (CHIKV), Zika virus (ZIKV) and West Nile virus (WNV). Experiments were performed under different climate conditions (27 ± 5 °C; 24 ± 5 °C) for fourteen days. Ae. koreicus had the potential to transmit CHIKV and ZIKV but not WNV. Transmission was exclusively observed at the higher temperature, and transmission efficiency was rather low, at 4.6% (CHIKV) or 4.7% (ZIKV). Using a whole virome analysis, a novel mosquito-associated virus, designated Wiesbaden virus (WBDV), was identified in Ae. koreicus. Linking the WBDV infection status of single specimens to their transmission capability for the arboviruses revealed no influence on ZIKV transmission. In contrast, a coinfection of WBDV and CHIKV likely has a boost effect on CHIKV transmission. Due to its current distribution, the risk of arbovirus transmission by Ae. koreicus in Europe is rather low but might gain importance, especially in regions with higher temperatures. The impact of WBDV on arbovirus transmission should be analyzed in more detail.     

Releasing incompatible males drives strong suppression across populations of wild and Wolbachia-carrying Aedes aegypti in Australia

Releasing sterile or incompatible male insects is a proven method of population management in agricultural systems with the potential to revolutionize mosquito control. Through a collaborative venture with the “Debug” Verily Life Sciences team, we assessed the incompatible insect technique (IIT) with the mosquito vector Aedes aegypti in northern Australia in a replicated treatment control field trial. Backcrossing a US strain of Ae. aegypti carrying Wolbachia wAlbB from Aedes albopictus with a local strain, we generated a wAlbB2-F4 strain incompatible with both the wild-type (no Wolbachia) and wMel-Wolbachia Ae. aegypti now extant in North Queensland. The wAlbB2-F4 strain was manually mass reared with males separated from females using Verily sex-sorting technologies to obtain no detectable female contamination in the field. With community consent, we delivered a total of three million IIT males into three isolated landscapes of over 200 houses each, releasing ∼50 males per house three times a week over 20 wk. Detecting initial overflooding ratios of between 5:1 and 10:1, strong population declines well beyond 80% were detected across all treatment landscapes when compared to controls. Monitoring through the following season to observe the ongoing effect saw one treatment landscape devoid of adult Ae. aegypti early in the season. A second landscape showed reduced adults, and the third recovered fully. These encouraging results in suppressing both wild-type and wMel-Ae. aegypti confirms the utility of bidirectional incompatibility in the field setting, show the IIT to be robust, and indicate that the removal of this arbovirus vector from human-occupied landscapes may be achievable.

Mosquitoes transmit parasites and viruses that infect hundreds of millions of humans annually. Globally, one invasive species—Aedes aegypti (Linnaeus)—is responsible for the greatest transmission of arboviruses, causing diseases including yellow fever, dengue, chikungunya, and Zika (1). The paucity of effective vaccines for most of these diseases and observed concerns for both growing insecticide resistance and insecticide’s adverse effects on other beneficial species have prompted renewed interest in species-specific biological control methods (2).Releasing sterile or incompatible male insects en masse is one method of insect population control currently under development (3). The sterile insect technique (SIT) uses the release of sterile male insects that search and mate with wild females to prevent subsequent production of offspring. The SIT has been successfully used to control various insect pest species (4), including the New World screwworm fly (5), the tsetse fly (6), the Mediterranean fruit fly (7), and the apple codling moth (8). Previous SIT technologies have been hampered by their need for radiation or chemical sterilents, which can compromise male fitness, requiring the release of more sterile males to compensate for their fitness decline (9, 10). Furthermore, the development of genetic modification to generate sterile male Ae. aegypti mosquitoes has been hampered by perceived environmental risks as well as strong regulatory issues and community acceptance (11).The first applications of SIT to mosquitoes encountered mixed successes during the 1970s and ’80s (12), as it proved difficult to produce sufficient numbers of competitive sterile males to suppress natural populations. More recently, elegant transgenic approaches have generated sterile male mosquitoes for the malaria vector Anopheles gambiae (13), the dengue vector Ae. aegypti (3, 14), and the Asian tiger mosquito Aedes albopictus (15). Releases of transgenic sterile Ae. aegypti by Oxitec Ltd in Grand Cayman have demonstrated an effective reduction of these mosquitoes (16).Reproductively incompatible males can now be produced using a maternally inherited gram-negative endosymbiotic bacterium Wolbachia pipientis (17, 18). Many of these strains carry a cytoplasmic incompatibility (CI) phenotype, where males of one Wolbachia strain can be reproductively incompatible with females that do not carry the strain; thus, females lay eggs that fail to hatch (18). This scenario provides an opportunity to reassess the SIT using what is now termed the incompatible insect technique [IIT (19)]. The SIT is generally more effective when females are not released (20), as sterile female insects can still damage crops, transmit disease, or simply distract sterile males from searching out wild mates. In the case of mosquito SIT and IIT, releasing males means only releasing mosquitoes which do not bite, have fewer risks, and encourage community acceptance.The primary aim for this study was to demonstrate the effectiveness of an Ae. aegypti IIT in a replicated treatment control study using males infected with a Wolbachia wAlbB strain from Ae. albopictus. Australia’s northern Queensland towns have endemic populations of Ae. aegypti (21), some of which have recently been transformed to carry the wMel Wolbachia strain (transfected from Drosophila melanogaster) in order to reduce arbovirus transmission risk (22): this phenotype provides arbovirus-blocking properties (23). We hypothesized that by selecting isolated towns and suburbs in tropical northern Queensland, we could demonstrate strong Ae. aegypti suppression over one season. By monitoring over the following season, we also sought to test whether suppression during one season would have a subsequent impact on populations the following season. At the outset of this study, all Ae. aegypti populations in the study site were wild type (no Wolbachia). However, during preparations for our IIT experiment—and at the request of the Queensland state health authority—all experimental landscape populations were transformed by high levels of wMel-infected Ae. aegypti released by Eliminate Dengue (now the World Mosquito Program [WMP]) (24). Subsequently, we released wAlbB2-infected males into a mosaic population of both wild type and wMel-Ae. aegypti to induce incompatible mating. We observed strong suppression over 20 wk, with bidirectional incompatibility in a field setting—and evidence of an ongoing suppression effect lasting into the next season.     

A Novel Anphevirus in Aedes albopictus Mosquitoes Is Distributed Worldwide and Interacts with the Host RNA Interference Pathway

The Asian tiger mosquito Aedes albopictus is a competent vector for several human arboviruses including dengue, chikungunya and Zika viruses. Mosquitoes also harbor insect-specific viruses (ISVs) that may modulate host physiology and potentially affect the transmission of viruses that are pathogenic to vertebrates, thus representing a potential tool for vector control strategies. In Ae. albopictus we identified a novel anphevirus (family Xinmoviridae; order Mononegavirales) provisionally designated here as Aedes albopictus anphevirus (AealbAV). AealbAV contains a ~12.4 kb genome that is highly divergent from currently known viruses but displays gene content and genomic organization typical of known anpheviruses. We identified AealbAV in several publicly available RNA-Seq datasets from different geographical regions both in laboratory colonies and field collected mosquitoes. Coding-complete genomes of AealbAV strains are highly similar worldwide (>96% nucleotide identity) and cluster according to the geographical origin of their hosts. AealbAV appears to be present in various body compartments and mosquito life stages, including eggs. We further detected AealbAV-derived vsiRNAs and vpiRNAs in publicly available miRNA-Seq libraries of Ae. albopictus and in samples experimentally coinfected with chikungunya virus. This suggests that AealbAV is targeted by the host RNA interference (RNAi) response, consistent with persistent virus replication. The discovery and characterization of AealbAV in Ae. albopictus will now allow us to identify its infection in mosquito populations and laboratory strains, and to assess its potential impact on Ae. albopictus physiology and ability to transmit arboviruses.     

Genetic Adaptation by Dengue Virus Serotype 2 to Enhance Infection of Aedes aegypti Mosquito Midguts

Dengue viruses (DENVs), serotypes 1–4, are arthropod-borne viruses transmitted to humans by mosquitoes, primarily Aedes aegypti. The transmission cycle begins when Ae. aegypti ingest blood from a viremic human and the virus infects midgut epithelial cells. In studying viruses derived from the DENV2 infectious clone 30P-NBX, we found that when the virus was delivered to female Ae. aegypti in an infectious blood meal, the midgut infection rate (MIR) was very low. To determine if adaptive mutations in the DENV2 envelope (E) glycoprotein could be induced to increase the MIR, we serially passed 30P-NBX in Ae. aegypti midguts. After four passages, a single, non-conservative mutation in E protein domain II (DII) nucleotide position 1300 became dominant, resulting in replacement of positively-charged amino acid lysine (K) at position 122 with negatively-charged glutamic acid (E; K122E) and a significantly-enhanced MIR. Site directed mutagenesis experiments showed that reducing the positive charge of this surface-exposed region of the E protein DII correlated with improved Ae. aegypti midgut infection.