Evidence of vertical transmission of Zika virus in field-collected eggs of Aedes aegypti in the Brazilian Amazon

The effect of artificial light at night (ALAN) on the characteristics of diapause of Aedes albopictus

BACKGROUND

Recently, the effect of artificial light at night (ALAN) on the physiology and behavior of insects has gradually attracted the attention of researchers and has become a new research topic. Aedes albopictus is an important vector that poses a great public health risk. Further studies on the diapause of Ae. albopictus can provide a basis for new vector control, and it is also worth exploring whether the effect of ALAN on the diapause of Ae. albopictus will provide a reference for the prevention and control of infectious diseases mediated by Ae. albopictus.

METHODS

In this study, we experimentally studied the diapause characteristics of different geographical strains of Ae. albopictus under the interference of ALAN, explored the effect of ALAN on the diapause of Ae. albopictus and explored the molecular mechanism of ALAN on the diapause process through RNA-seq.

RESULTS

As seen from the diapause incidence, Ae. albopictus of the same geographic strain showed a lower diapause incidence when exposed to ALAN. The differentially expressed genes (DEGs) were mainly enriched in signaling and metabolism-related pathways in the parental females and diapause eggs of the ALAN group.

CONCLUSIONS

ALAN inhibits Ae. albopictus diapause. In the short photoperiod induced diapause of Ae. albopictus in temperate strain Beijing and subtropical strain Guangzhou, the disturbance of ALAN reduced the egg diapause rate and increased the egg hatching rate of Ae. albopictus, and the disturbance of ALAN also shortened the life cycle of Ae. albopictus eggs after hatching.

Detection of arboviruses in Aedes aegypti through transovarian analysis: A study in Goiânia, Goiás

BACKGROUND

Arboviral diseases are a group of infectious diseases caused by viruses transmitted by arthropods, mainly mosquitoes. These diseases, such as those caused by the dengue (DENV), Zika (ZIKV), chikungunya (CHIKV), and yellow fever (YFV) viruses, have a significant impact worldwide. In this context, entomological surveillance plays a crucial role in the control and prevention of arboviruses by providing essential information on the presence, distribution, and activity of vector mosquitoes. Based on entomological surveillance, transovarian transmission provides information regarding the maintenance and dissemination of arboviruses. The objective of this study was to detect these arboviruses in Goiânia, Goiás, and analyze the occurrence of transovarian transmission.

METHODS

Aedes aegypti eggs were collected from different regions of Goiânia and cultivated under controlled laboratory conditions until the emergence of adult mosquitoes. Adult females were grouped into pools containing their heads and thoraxes. These pools were subsequently evaluated using reverse-transcription quantitative polymerase chain reaction (RT-qPCR) assay.

RESULTS

A total of 157 pools (N=1570) were analyzed, with two pools testing positive for CHIKV and one pool testing positive for ZIKV, indicating that the offspring resulting from transovarian transmission are potentially infectious.

CONCLUSIONS

In summary, the demonstration of the vertical transmission mechanisms of CHIKV and ZIKV in A. aegypti serves as an alert to health authorities, as these diseases are still underreported, and their primary urban vector has likely acquired this capacity, contributing to the dissemination of these infections.

The predicted potential distribution of Aedes albopictus in China under the shared socioeconomic pathway (SSP)1-2.6

Aedes albopictus (Skuse) (Diptera: Culicidae) is one of the 100 most invasive species in the world and represents a significant threat to public health. The distribution of Ae. albopictus has been expanding rapidly due to increased international trade, population movement, global warming and accelerated urbanization. Consequently, it is very important to know the potential distribution area of Ae. albopictus in advance for early warning and control of its spread and invasion. We randomly selected 282 distribution sites from 27 provincial-level administrative regions in China, and used the GARP and MaxEnt models to analyze and predict the current and future distribution areas of Ae. albopictus in China. The results showed that the current range of Ae. albopictus in China covers most provinces such as Yunnan and Guizhou Provinces, and the distribution of Ae. albopictus in border provinces such as Tibet, Gansu and Jilin Provinces tend to expand westwards. In addition, the potential distribution area of Ae. albopictus in China will continue to expand westwards due to future climate change under the SSP126 climate scenario. Furthermore, the results of environmental factor filtering showed that temperature and precipitation had a large effect on the distribution probability of Ae. albopictus.

Wolbachia wMel strain-mediated effects on dengue virus vertical transmission from Aedes aegypti to their offspring

BACKGROUND

Dengue virus serotypes (DENV-1 to -4) can be transmitted vertically in Aedes aegpti mosquitoes. Whether infection with the wMel strain of the endosymbiont Wolbachia can reduce the incidence of vertical transmission of DENV from infected females to their offspring is not well understood.

METHODS

A laboratory colony of Vietnamese Ae. aegypti, both with and without wMel infection, were infected with DENV-1 by intrathoracic injection (IT) to estimate the rate of vertical transmission (VT) of the virus. VT in the DENV-infected mosquitoes was calculated via the infection rate estimation from mosquito pool data using maximum likelihood estimation (MLE).

RESULTS

In 6047 F1 Vietnamese wild-type Ae. aegypti, the MLE of DENV-1 infection was 1.49 per 1000 mosquitoes (95% confidence interval [CI] 0.73-2.74). In 5500 wMel-infected Ae. aegypti, the MLE infection rate was 0 (95% CI 0-0.69). The VT rates between mosquito lines showed a statistically significant difference.

CONCLUSIONS

The results reinforce the view that VT is a rare event in wild-type mosquitoes and that infection with wMel is effective in reducing VT.

Arbovirus detection in synanthropic mosquitoes from the Brazilian Amazon and in mosquito saliva using Flinders Technology Associates cards

Although arbovirus transmission and identifying target vectors may provide a baseline for planning disease control strategies, there are many gaps in knowledge regarding these mosquitoes and viral species in urban, rural, or sylvatic habitats in the Brazilian Amazon. Our goal was to screen for dengue, chikungunya, and Zika viruses in synanthropic mosquitoes and with Flinders Technology Associates (FTA) cards using insect saliva. Mosquitoes were caught using ovitraps and aspirators in the city of Porto Velho, Rondônia, Brazil. Honey-baited FTA cards were placed in mosquito cages for 15 days; whole mosquitoes and FTA cards were analysed for viral RNA using RT-qPCR assays. One pool of Aedes aegypti females was found to be infected with the Zika virus and one male mosquito was infected with dengue-4, suggesting natural vertical/venereal transmission. Our study also reported evidence of vertical/venereal transmission of ZIKV in Culex quinquefasciatus males for the first time in the Brazilian Amazon, and the feasibility of using FTA cards to detect arboviruses in the saliva of field-collected mosquitoes. Vertical/venereal transmission of viruses by atypical mosquito species reinforces the need for combined viral and entomological screening in arbovirus surveillance programs.

Surveillance of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) as a Method for Prevention of Arbovirus Transmission in Urban and Seaport Areas of the Southern Coast of Brazil

Entomological surveillance is a traditional method to measure presence, distribution, and seasonal variation of vectors in urban areas, and is essential to targeted control activities to prevent arbovirus transmission. Ovitraps as one of the main components of surveillance programs, enable determination of female oviposition behavior, as well as identification of seasonal variations of the vector. The goals of this study were 1) to detect the mosquitos (Aedes aegypti Linnaeus) and (Aedes albopictus Skuse) (Diptera:Culicidae), in Paranaguá city, 2) to assess ovitrap positive index (OPI), egg density index (EDI), and their relationship with meteorological variables, and 3) to evaluate the vertical transmission of dengue, Zika, and chikungunya in Ae. aegypti and Ae. albopictus. The study was carried out in urban areas of Paranaguá city, an important port region of Brazil, from June 2017 to November 2018. The city was divided into 16 area-clusters. Three-hundred and thirty-one ovitraps were installed monthly, remaining for four days in selected places. Kernel density maps were done to compare the spatiotemporal distribution of collected eggs. Areas which maintained constant oviposition associated with vector activity were identified and were found to overlap the area-clusters with the highest EDI. As viral RNA was not detected, vertical transmission was likely not a maintenance mechanism of arbovirus circulation in Ae. aegypti and Ae. albopictus vectors. This study reiterates the importance, efficiency, and feasibility of ovitraps to monitor the presence and dynamics of Aedes spp. populations.

Entomo-Virological Aedes aegypti Surveillance Applied for Prediction of Dengue Transmission: A Spatio-Temporal Modeling Study

Currently, DENV transmitted primarily by Aedes aegypti affects approximately one in three people annually. The spatio-temporal heterogeneity of vector infestation and the intensity of arbovirus transmission require surveillance capable of predicting an outbreak. In this work, we used data from 4 years of reported dengue cases and entomological indicators of adult Aedes collected from approximately 3500 traps installed in the city of Foz do Iguaçu, Brazil, to evaluate the spatial and temporal association between vector infestation and the occurrence of dengue cases. Entomological (TPI, ADI and MII) and entomo-virological (EVI) indexes were generated with the goal to provide local health managers with a transmission risk stratification that allows targeting areas for vector control activities. We observed a dynamic pattern in the evaluation; however, it was a low spatio-temporal correlation of Ae. aegypti and incidence of dengue. Independent temporal and spatial effects capture a significant portion of the signal given by human arbovirus cases. The entomo-virological index (EVI) significantly signaled risk in a few areas, whereas entomological indexes were not effective in providing dengue risk alert. Investigating the variation of biotic and abiotic factors between areas with and without correlation should provide more information about the local epidemiology of dengue.

Chikungunya (Togaviridae) and dengue 2 (Flaviviridae) viruses detected from Aedes aegypti mosquitoes in Burkina Faso by qRT-PCR technique: Preliminary results and perspective for molecular characterization of arbovirus circulation in vector populations

In 2016, an entomological study was carried out in a railway transect between Banfora and Ouagadougou, Burkina Faso. The objective was to assess the risk factors of arbovirus outbreaks, including vector-borne infection status within representative regions of the country. Aedes aegypti mosquitoes were collected at the larval stage from their natural rearing habitats in four study sites when estimating the main larval index, then reared until adult stage and kept in RNAlater for the detection of arbovirus RNA. In the laboratory, mosquito samples were tested for dengue virus (DENV) and Chikungunya virus (CHIKV) using a real-time qRT-PCR stage. A DENV-2 positive pool was detected in Ouagadougou with a minimum infection rate (MIR) of 16.67 and other six CHIKV-positive pools with a MIR of 66.67 in Ouagadougou, Banfora, and Boromo. This qRT-PCR approach, if validated with various samples also comprising wild blood-fed adults, is a useful tool for arbovirus circulation and disease monitoring in Burkina Faso.

Natural vertical cotransmission of Dengue virus and Chikungunya virus from Aedes aegypti in Brumado, Bahia, Brazil

BACKGROUND

Arthropod-borne viruses have recently emerged and are pathogens of various human diseases, including dengue, zika, and chikungunya viruses.

METHODS

We collectedAedes aegyptilarvae (N = 20) from Brumado, Bahia, Brazil, and treated and individually preserved the specimens. We analyzed the samples for dengue, zika, and chikungunya viruses using molecular biology methods.

RESULTS

We found that 25% (N = 5) and 15% (N = 3) were positive exclusively for dengue and chikungunya viruses, respectively; 15% (N = 3) were coinfected with both.

CONCLUSIONS

This is the first report of dengue and chikungunya virus coinfection in A. aegypti larvae.

Natural Aedes-Borne Virus Infection Detected in Male Adult Aedes aegypti (Diptera: Culicidae) Collected From Urban Settings in Mérida, Yucatán, México

Aedes-borne viruses (ABVs) such as dengue (DENV), chikungunya (CHIKV), and Zika (ZIKV) contribute significantly to the global burden of infectious diseases, disproportionately affecting disadvantaged populations from tropical and subtropical urban areas. ABVs can be transmitted from female mosquitoes to their progeny by vertical transmission via transovarial and/or trans-egg vertical transmission and contribute to the maintenance of infected-mosquito populations year-round in endemic regions. This study describes the natural infection rate of DENV, CHIKV, and ZIKV in field-caught male Aedes (Sergentomyia) aegypti (Linnaeus) mosquitoes from Mérida, Yucatán, México, as a proxy for the occurrence of vertical virus transmission. We used indoor sequential sampling with Prokopack aspirators to collect all mosquitoes inside houses from ABV hotspots areas. Collections were performed in a DENV and CHIKV post-epidemic phase and during a period of active ZIKV transmission. We individually RT-qPCR tested all indoor collected Ae. aegypti males (1,278) followed by Sanger sequencing analysis for final confirmation. A total of 6.7% male mosquitoes were positive for ABV (CHIKV = 5.7%; DENV = 0.9%; ZIKV = 0.1%) and came from 21.0% (30/143) houses infested with males. Most ABV-positive male mosquitoes were positive for CHIKV (84.8%). The distribution of ABV-positive Ae. aegypti males was aggregated in a few households, with two houses having 11 ABV-positive males each. We found a positive association between ABV-positive males and females per house. These findings suggested the occurrence of vertical arbovirus transmission within the mosquito populations in an ABV-endemic area and, a mechanism contributing to viral maintenance and virus re-emergence among humans in post-epidemic periods.

Survival and Replication of Zika Virus in Diapause Eggs of Aedes Albopictus From Beijing, China

Zika virus (ZIKV) has emerged as a globally important arbovirus. The virus is primarily transmitted to humans through the bite of an infective Aedes albopictus in temperate area. Vertical transmission of ZIKV by Ae. albopictus is determined and has been suggested to be a means by which the virus could persist in nature. Ae. albopictus undergoes a well-characterized photoperiodic diapause. Viruses are harbored by overwintering mosquitoes in diapause that contributes to the resurgence of vertebrate diseases in the following spring, yet little is known about the impact of diapause on the regulation of viral replication and survival. The purpose of this study is to determine that Ae. albopictus in Beijing are highly susceptible to ZIKV (92.3%), and viable virus is passed to their organs of progeny via vertical transmission. Moreover, diapause eggs (diapause incidence 97.8%) had significantly lower minimum infection rates and filial infection rates of the first gonotrophic cycle than those of the second gonotrophic cycle in the short-day photoperiod group. Regarding the development of diapause eggs, the minimum infection rates and ZIKV RNA copy number increased significantly, suggesting that virus RNA replication occurred in the diapause eggs. Meanwhile, eggs from the ZIKV-infected mosquitoes had a significantly lower hatching rate compared with uninfected mosquitoes, implying an intriguing interaction between diapause eggs and virus. The findings here suggest that vertical transmission of ZIKV from diapause eggs to progeny may have a critical epidemiological role in the dissemination and maintenance of ZIKV circulating in the vector.

Resource availability for the mosquito Aedes aegypti affects the transmission mode evolution of a microsporidian parasite

Ecological conditions may greatly affect the relative importance of vertical and horizontal transmission, in particular for parasites with a mixed mode of transmission. Resource availability is one important environmental factor, affecting host growth and fecundity, but also the parasite’s own development. The consequences for the potential of vertical and horizontal transmission and for the evolution of transmission mode are largely unknown. We let the mixed-mode microsporidian parasite Edhazardia aedis evolve on its mosquito host Aedes aegypti under high-food or low-food conditions, representing permissive and restricted conditions. These alter the timing of development of infected larvae and thereby the probabilities for the parasites to enter the vertical or horizontal transmission pathways. After 10 generations, evolved parasites were assayed under the two food levels. There was an ecological trade-off between transmission modes, mediated by nutrient effects on host development, resulting in a higher vertical transmission (VT) potential under high-food and a higher horizontal transmission (HT) potential under low-food test conditions. Evolution under high food increased the VT potential of the parasite, particularly if it was tested at low food. This involved higher probability of carrying binucleate spores for the emerging females, greater fecundity and a longer life compared to parasites that were tested in the same conditions but had evolved under low food. The changes are related to the developmental regulation and switch in the production of two spore types, affecting investment in VT or HT. In contrast, the HT potential remained relatively unaffected by the parasite’s evolutionary history, suggesting that, within our experiential design, the VT mode evolved independently of the HT mode. Our work illustrates the possible links between resource availability, within-host developmental processes and the evolution of parasite transmission investment. Future work, theoretical and experimental, should scale up from within-host to between-host levels, including eco-evolutionary and epidemiological dynamics.

A highly sensitive strand-specific multiplex RT-qPCR assay for quantitation of Zika virus replication

Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) is widely used to quantify viral RNA genomes for diagnostics and research, yet conventional RT-qPCR protocols are unable to accurately distinguish between the different viral RNA species that exist during infection. Here we show that false-priming and self-priming occur during reverse transcription with several published Zika virus (ZIKV) primer sets. We developed a RT-qPCR assay using tagged primers and thermostable reverse transcriptase, which greatly reduced the occurrence of nonspecific cDNA products. Furthermore, we optimized the assay for use in multiplex qPCR which allows for simultaneous quantitative detection of positive-strand and negative-strand ZIKV RNA along with an internal control from both human and mosquito cells. Importantly, this assay is sensitive enough to study early stages of virus infection in vitro. Strikingly, using this assay, we detected ZIKV negative-strand RNA as early as 3 h post-infection in mammalian cell culture, at a time point prior to the onset of positive-strand RNA synthesis. Overall, the strand-specific RT-qPCR assay developed herein is a valuable tool to quantify ZIKV RNA and to study viral replication dynamics during infection. The application of these findings has the potential to increase accuracy of RNA detection methods for a variety of viral pathogens.

LAMP Detection of Virus-Derived DNA of Zika Virus in Vector Mosquito

Detection of infectious viruses in mosquitoes is one of the prerequisite measures to monitor the prevalence of vector-borne viral diseases. Determining which mosquitoes are currently infected with arboviruses such as Zika, dengue, and chikungunya virus is not yet practical in endemic areas due to multiple causes including the difficulty of dealing with the virus’ unstable RNA. In this study, instead of handling viral RNA, virus-derived DNA (vDNA) was introduced as a target template for nucleic acid amplification. In combination with loop-mediated isothermal amplification (LAMP), we examined a LAMP-based vDNA detection assay (vDNA-LAMP) targeting Zika virus (ZIKV). The vDNA-LAMP reaction amplifying part of the NS3 region of ZIKV successfully detected its vDNA from crude DNA purified from artificially infected cultured cells and Aedes mosquitoes. This rapid, simple, and versatile method may provide a promising field-surveillance method for arbovirus circulation via vector mosquitoes.

Route of Zika virus infection in Aedes aegypti by transmission electron microscopy

Background

Zika fever has been a global health security threat, especially in the tropical and subtropical regions where most of the cases occur. The disease is caused by Zika virus (ZIKV), which belongs to the family Flaviviridae, genus Flavivirus. The virus is transmitted by Aedes mosquitoes, mostly by Aedes aegypti, during its blood meal. In this study we present a descriptive analysis, by transmission electron microscopy (TEM), of ZIKV infection in A. aegypti elected tissues at the 3rd day of infection. ZIKV vertical transmission experiments by oral infection were conducted to explore an offspring of natural infection.

Results

Gut and ovary tissues harbored a higher number of viral particles. The ZIKV genome was also detected, by RT-qPCR technique, in the organism of orally infected female mosquitoes and in their eggs laid.

Conclusions

The data obtained suggest that the ovary is an organ susceptible to be infected with ZIKV and that virus can be transmitted from mother to a fraction of the progeny.

Actions of Camptothecin Derivatives on Larvae and Adults of the Arboviral Vector Aedes aegypti

Mosquito-borne viruses including dengue, Zika, and Chikungunya viruses, and parasites such as malaria and Onchocerca volvulus endanger health and economic security around the globe, and emerging mosquito-borne pathogens have pandemic potential. However, the rapid spread of insecticide resistance threatens our ability to control mosquito vectors. Larvae of Aedes aegypti were screened with the Medicines for Malaria Venture Pandemic Response Box, an open-source compound library, using INVAPP, an invertebrate automated phenotyping platform suited to high-throughput chemical screening of larval motility. We identified rubitecan (a synthetic derivative of camptothecin) as a hit compound that reduced A. aegypti larval motility. Both rubitecan and camptothecin displayed concentration dependent reduction in larval motility with estimated EC50 of 25.5 ± 5.0 µM and 22.3 ± 5.4 µM, respectively. We extended our investigation to adult mosquitoes and found that camptothecin increased lethality when delivered in a blood meal to A. aegypti adults at 100 µM and 10 µM, and completely blocked egg laying when fed at 100 µM. Camptothecin and its derivatives are inhibitors of topoisomerase I, have known activity against several agricultural pests, and are also approved for the treatment of several cancers. Crucially, they can inhibit Zika virus replication in human cells, so there is potential for dual targeting of both the vector and an important arbovirus that it carries.

Virome in adult Aedes albopictus captured during different seasons in Guangzhou City, China

Background

The mosquito Aedes albopictus is an important vector for many pathogens. Understanding the virome in Ae. albopictus is critical for assessing the risk of disease transmission, implementation of vector control measures, and health system strengthening.

Methods

In this study, viral metagenomic and PCR methods were used to reveal the virome in adult Ae. albopictus captured in different areas and during different seasons in Guangzhou, China.

Results

The viral composition of adult Ae. albopictus varied mainly between seasons. Over 50 viral families were found, which were specific to vertebrates, invertebrates, plants, fungi, bacteria, and protozoa. In rural areas, Siphoviridae (6.5%) was the most common viral family harbored by mosquitoes captured during winter and spring, while Luteoviridae (1.1%) was the most common viral family harbored by mosquitoes captured during summer and autumn. Myoviridae (7.0% and 1.3%) was the most common viral family in mosquitoes captured in urban areas during all seasons. Hepatitis B virus (HBV) was detected by PCR in a female mosquito pool. The first near full-length HBV genome from Ae. albopictus was amplified, which showed a high level of similarity with human HBV genotype B sequences. Human parechovirus (HPeV) was detected in male and female mosquito pools, and the sequences were clustered with HPeV 1 and 3 sequences.

Conclusions

Large numbers of viral species were found in adult Ae. albopictus, including viruses from vertebrates, insects, and plants. The viral composition in Ae. albopictus mainly varied between seasons. Herein, we are the first to report the detection of HPeV and HBV in mosquitoes. This study not only provides valuable information for the control and prevention of mosquito-borne diseases, but it also demonstrates the feasibility of xenosurveillance.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04922-z.

Zika virus infects Aedes aegypti ovaries

Pathogens are transmitted from one host to another either by vertical transmission (VT) or horizontal transmission (HT). Mosquito-borne arboviruses (arthropod-borne viruses), including several clinically important viruses such as dengue, Zika, West Nile and chikungunya viruses persist in nature by both VT and HT. VT may also serve as an essential link in the transmission cycle during adverse environmental conditions. VT rates (VTRs) vary between virus families and even among viruses within the same genus. The mechanism behind these differences in VTRs among viruses is poorly understood. For efficient VT to occur, viruses must infect the mosquito germline. Here, we show that Zika virus infects mosquito ovaries and is transmitted vertically at a low rate. The infected progeny derive from mosquitoes with infected ovaries. The prevalence of ovary infection increases after a second non-infectious blood meal following an infectious blood meal.

Natural Infection and Vertical Transmission of Zika Virus in Sylvatic Mosquitoes Aedes albopictus and Haemagogus leucocelaenus from Rio de Janeiro, Brazil

Zika virus (ZIKV) was recently introduced into the Western Hemisphere, where it is suspected to be transmitted mainly by Aedes aegypti in urban environments. ZIKV represents a public health problem as it has been implicated in congenital microcephaly in South America since 2015. Reports of ZIKV transmission in forested areas of Africa raises the possibility of its dispersal to non-human-modified environments in South America, where it is now endemic. The current study aimed to detect arboviruses in mosquitoes collected from areas with low human interference in Rio de Janeiro, Brazil. Using a sensitive pan-flavivirus RT-PCR, designed to detect the NS5 region, pools of Ae. albopictus and Haemagogus leucocelaenus, were positive for both ZIKV and yellow fever (YFV). Virus RNA was detected in pools of adult males and females reared from field-collected eggs. Findings presented here suggest natural vertical transmission and infection of ZIKV in Hg. leucocelaenus and Ae.albopitcus in Brazil.

Evidence of Zika virus horizontal and vertical transmission in Aedes albopictus from Spain but not infectious virus in saliva of the progeny

Aedes albopictus mosquitoes have been experimentally demonstrated to be a competent vector for Zika virus (ZIKV) in different countries, but there are still some gaps related to the importance of Ae. albopictus in ZIKV transmission. Recent studies on Spanish Ae. albopictus populations showed controversial results for ZIKV transmission and no studies have been performed yet to detect infectious ZIKV in saliva of progeny of infected female mosquitoes. Herein, the horizontal transmission (HT) and vertical transmission (VT) of ZIKV in field-collected Ae. albopictus mosquitoes from Spain were evaluated for ZIKV strains (African I and Asian lineages) to better estimate the risk of ZIKV transmission by Ae. albopictus. The two field-collected Ae. albopictus populations assayed were infected by all tested ZIKV strains, however differences in terms of vector competence were detected depending on strain-population combination. Moreover, a higher susceptibility to the African I lineage strain than to the Asian lineage strain was observed in both mosquito populations. On the other hand, VT was demonstrated for both ZIKV lineages, detecting the virus in both males and females of the progeny of infected females, although importantly ZIKV dissemination and transmission were not detected in the infected females from the offspring. The results of the present study demonstrate that Spanish Ae. albopictus populations could sustain virus transmission in case of ZIKV introduction, but VT would play a poor role in the ZIKV epidemiology. Overall, our results provide helpful information to health authorities to establish efficient surveillance and vector control programmes for ZIKV.

Modeling and mapping the habitat suitability and the potential distribution of Arboviruses vectors in Morocco

Mosquitoes transmit several agents of diseases and the presence of different species represents a threat to animal and public health. Aedes and Culex mosquitoes are of particular concern giving their potential vector competence for Arbovirus transmission. In Morocco, the lack of detailed information related to their spatial distribution raises major concerns and hampers effective vector surveillance and control. Using maximum entropy (Maxent) modeling, we generated prediction models for the potential distribution of Arboviruses vectors (Aedes aegypti, Ae. vexans, Ae. caspius, Ae. detritus, and Culex pipiens) in Morocco, under current climatic conditions. Also, we investigated the habitat suitability for the potential occurrence and establishment of Ae. albopictus and Ae. vittatus recorded only once in the country. Prediction models for these last two species were generated considering occurrence datasets from close countries of the Mediterranean Basin, where Ae. albopictus is well established, and from a worldwide database for the case of Ae. vittatus (model transferability). With the exception of Ae. vittatus, the results identify potential habitat suitability in Morocco for all mosquitos considered. Existing areas with maximum risk of establishment and high potential distribution were mainly located in the northwestern and central parts of Morocco. Our results essentially underline the assumption that Ae. albopictus, if not quickly controlled, might find suitable habitats and has the potential to become established, especially in the northwest of the country. These findings may help to better understand the potential distribution of each species and enhance surveillance efforts in areas identified as high risk.

Rapid evolution of enhanced Zika virus virulence during direct vertebrate transmission chains

Zika virus (ZIKV) has the unusual capacity to circumvent natural alternating mosquito-human transmission and be directly transmitted human-to-human via sexual and vertical routes. The impact of direct transmission on ZIKV evolution and adaptation to vertebrate hosts is unknown. Here we show that molecularly barcoded ZIKV rapidly adapted to a mammalian host during direct transmission chains in mice, coincident with the emergence of an amino acid substitution previously shown to enhance virulence. In contrast, little to no adaptation of ZIKV to mice was observed following chains of direct transmission in mosquitoes or alternating host transmission. Detailed genetic analyses revealed that ZIKV evolution in mice was generally more convergent and subjected to more relaxed purifying selection than in mosquitoes or alternate passages. These findings suggest that prevention of direct human transmission chains may be paramount to resist gains in ZIKV virulence.Importance We used experimental evolution to model chains of direct and indirect Zika virus (ZIKV) transmission by serially passaging a synthetic swarm of molecularly barcoded ZIKV within and between mosquitoes and mice. We observed that direct mouse transmission chains facilitated a rapid increase in ZIKV replication and enhanced virulence in mice. These findings demonstrate that ZIKV is capable of rapid adaptation to a vertebrate host and indicate that direct human-to-human transmission could pose a greater threat to public health than currently realized.

Genomic and Epidemiological Surveillance of Zika Virus in the Amazon Region

Zika virus (ZIKV) has caused an explosive epidemic linked to severe clinical outcomes in the Americas. As of June 2018, 4,929 ZIKV suspected infections and 46 congenital syndrome cases had been reported in Manaus, Amazonas, Brazil. Although Manaus is a key demographic hub in the Amazon region, little is known about the ZIKV epidemic there, in terms of both transmission and viral genetic diversity. Using portable virus genome sequencing, we generated 59 ZIKV genomes in Manaus. Phylogenetic analyses indicated multiple introductions of ZIKV from northeastern Brazil to Manaus. Spatial genomic analysis of virus movement among six areas in Manaus suggested that populous northern neighborhoods acted as sources of virus transmission to other neighborhoods. Our study revealed how the ZIKV epidemic was ignited and maintained within the largest urban metropolis in the Amazon. These results might contribute to improving the public health response to outbreaks in Brazil.

Simultaneous circulation of zakat, dengue, and chikungunya viruses and their vertical co-transmission among Aedes aegypti

The outbreaks caused by the Aedes aegypti-transmitted dengue virus (DENV), zakat virus (ZIKV), and chikungunya virus (CHIKV) result in a significant impact to the health systems of tropical countries. Furthermore, the occurrence of patients coinfected by at least two of these arboviruses is an aggravating factor in that scenario. On this basis, surveillance tools such as the Rapid Index Survey for Aedes aegypti (LIRAa) are used to estimate vector infestation in order to improve the prediction of human outbreaks. Ae. aegypti eggs were collected in the city of Vitória da Conquista, in Bahia State, Brazil, and subsequently hatched into larvae, which were analyzed in pools or individually for the presence of DENV, ZIKV, and CHIKV by molecular biology methods. The detection data for arboviruses were crossed with the LIRAa obtained in each region of the study city. Thirty larvae pools were analyzed, and fourteen (46.6%) of them were detected positive for DENV, ZIKV, and/or CHIKV. Among the individually analyzed larvae (n = 30), nine (30%) were positive for any of these arboviruses, and four (13.3%) were simultaneously coinfected by DENV and ZIKV. Furthermore, there was a positive correlation between the detection of circulating arboviruses and LIRAa. The simultaneous Ae. aegypti larvae infection by two different arboviruses is an unprecedented finding. This result suggests the occurrence of a vertical arboviruses co-transmission from the female mosquito to its offspring in nature. The occurrence of concomitant circulation of DENV, ZIKV, and CHIKV in Ae. aegypti from a single study region is another finding of this article. Finally, LIRAa seems to not only estimate vector infestation but also to predict circulation of arboviruses.

Vertical transmission of zika virus in Aedes albopictus

Background

Zika virus (ZIKV) is an arthropod-borne flavivirus transmitted by Aedes mosquitoes. Aedes albopictus is an important vector of ZIKV worldwide. To date, most experiments have focused on the vertical transmission of ZIKV in Ae. aegypti, while studies on Ae. albopictus are very limited. To explore vertical transmission in Ae. albopictus, a series of laboratory studies were carried out.

Methodology/Principal findings

In this study, Ae. albopictus were blood-fed with ZIKV-infectious blood, and the ovaries and offspring viral infection rates were analyzed by reverse transcription PCR (RT-PCR), real-time reverse transcription PCR (RT-qPCR) and immunohistochemistry (IHC). ZIKV was detected in the ovaries and oviposited eggs in two gonotrophic cycles. The minimum filial egg infection rates in two gonotrophic cycles were 2.06% and 0.69%, and the effective population transmission rate was 1.87%. The hatching, pupation, and emergence rates of infected offspring were not significantly different from those of uninfected offspring, indicating that ZIKV did not prevent the offspring from completing the growth and development process. ZIKV was detected in three of thirteen C57BL/6 suckling mice bitten by ZIKV-positive F₁ females, and the viremia persisted for at least seven days.

Conclusions/Significance

ZIKV can be vertically transmitted in Ae. albopictus via transovarial transmission. The vertical transmission rates in F₁ eggs and adults were 2.06% and 1.87%, respectively. Even though the vertical transmission rates were low, the female mosquitoes infected via the congenital route horizontally transmitted ZIKV to suckling mice through bloodsucking. This is the first experimental evidence of offspring with vertically transmitted ZIKV initiating new horizontal transmission. The present study deepens the understanding of the vertical transmission of flaviviruses in Aedes mosquitoes and sheds light on the prevention and control of mosquito-borne diseases.

Zika virus (ZIKV) is a mosquito-borne flavivirus that poses a serious threat worldwide because of its associated serious neurological complications, such as Guillain-Barré syndrome in adults and microcephaly in newborns. Vertical transmission of ZIKV in humans has been confirmed. Furthermore, there have been reports of ZIKV infection in field-collected eggs, larvae and adult mosquitoes, which implies that ZIKV can also be vertically transmitted in mosquito vectors. However, the characteristics of vertical transmission of ZIKV in Aedes albopictus remain unclear. Here, we infected mosquitoes by allowing them to feed on an infectious blood meal. F₁ progeny (eggs and adults) from mosquitoes with ZIKV-positive ovaries were studied. Our results demonstrate that ZIKV can be vertically transmitted in Ae. albopictus via transovarial transmission. The female mosquitoes infected via the congenital route can horizontally transmit ZIKV to suckling mice through bloodsucking. These updated findings can be used for ZIKV disease prevention and vector control strategies.

Vertical Transmission of Zika Virus in Aedes aegypti Produces Potentially Infectious Progeny

Vertical transmission, or pathogen transfer from female to offspring, can facilitate the persistence of emerging arboviruses, such as Zika virus (ZIKV), through periods of low horizontal transmission or adverse environmental conditions. We aimed at determining the rate of vertical transmission for ZIKV in its principal vector, Aedes aegypti, and the vector competence of vertically infected progeny. Aedes aegypti females that consumed a blood meal provisioned with ZIKV were maintained under three temperature conditions (27°C, 30°C, and 33°C) following the infectious blood meal and allowed to complete three reproductive cycles. The overall vertical transmission rate was 6.5% (95% CI = 3.9-9.9). Vertical transmission of ZIKV was observed across all temperature conditions and virus detected in adult progeny up to 2 weeks postemergence. In total, 3.4% (95% CI = 1.6-6.2) of adult progeny produced saliva with ZIKV, indicating their vector competence. These results suggest the virus may be maintained in Ae. aegypti populations without a vertebrate host for short periods.

Highly Efficient Vertical Transmission for Zika Virus in Aedes aegypti after Long Extrinsic Incubation Time

While the Zika virus (ZIKV) 2014-2017 pandemic has subsided, there remains active transmission. Apart from horizontal transmission to humans, the main vector Aedes aegypti can transmit the virus vertically from mother to offspring. Large variation in vertical transmission (VT) efficiency between studies indicates the influence of parameters, which remain to be characterized. To determine the roles of extrinsic incubation time and gonotrophic cycle, we deployed an experimental design that quantifies ZIKV in individual progeny and larvae. We observed an early infection of ovaries that exponentially progressed. We quantified VT rate, filial infection rate, and viral load per infected larvae at 10 days post oral infection (d.p.i.) on the second gonotrophic cycle and at 17 d.p.i. on the second and third gonotrophic cycle. As compared to previous reports that studied pooled samples, we detected a relatively high VT efficiency from 1.79% at 10 d.p.i. and second gonotrophic cycle to 66% at 17 d.p.i. and second gonotrophic cycle. At 17 d.p.i., viral load largely varied and averaged around 800 genomic RNA (gRNA) copies. Longer incubation time and fewer gonotrophic cycles promoted VT. These results shed light on the mechanism of VT, how environmental conditions favor VT, and whether VT can maintain ZIKV circulation.

Entomological Surveillance Associated with Human Zika Cases in Miri Sarawak, Malaysia

Two confirmed human cases of Zika virus (ZIKV) were reported in the district of Miri, Sarawak, in 2016. Following that, a mosquito-based ZIKV surveillance study was conducted within 200-m radius from the case houses. Mosquito surveillance was conducted using five different methods, that is, biogents sentinel mosquito (BG) sentinel trap, modified sticky ovitrap, resting catch, larval surveillance, and conventional ovitrap. A total of 527 and 390 mosquito samples were obtained from the case houses in two localities, namely, Kampung Lopeng and Taman Shang Ri La, Miri, Sarawak, respectively. All mosquitoes collected were identified, which consisted of 11 species. Aedes albopictus, both the adult and larval stages, was the dominant species. Resting catch method obtained the highest number of adult mosquitoes (67%), whereas ovitrap showed the highest catch for larval mosquitoes (84%). Zika virus was detected in both adults and larvae of Ae. albopictus together with adults of Culex gelidus, and Culex quinquefasciatus using the real-time reverse transcriptase polymerase chain reaction (PCR) technique. It was noteworthy that Ae. albopictus positive with ZIKV were caught and obtained from four types of collection method. By contrast, Cx. gelidus and Culex quinquefasciatus adults collected from sticky ovitraps were also found positive with ZIKV. This study reveals vital information regarding the potential vectors of ZIKV and the possibility of transovarian transmission of the virus in Malaysia. These findings will be essentials for vector control program managers to devise preparedness and contingency plans of prevention and control of the arboviral disease.

The journey of Zika to the developing brain

Zika virus is a mosquito-borne Flavivirus originally isolated from humans in 1952. Following its re-emergence in Brazil in 2015, an increase in the number of babies born with microcephaly to infected mothers was observed. Microcephaly is a neurodevelopmental disorder, characterised phenotypically by a smaller than average head size, and is usually developed in utero. The 2015 outbreak in the Americas led to the World Health Organisation declaring Zika a Public Health Emergency of International Concern. Since then, much research into the effects of Zika has been carried out. Studies have investigated the structure of the virus, its effects on and evasion of the immune response, cellular entry including target receptors, its transmission from infected mother to foetus and its cellular targets. This review discusses current knowledge and novel research into these areas, in hope of developing a further understanding of how exposure of pregnant women to the Zika virus can lead to impaired brain development of their foetus. Although no longer considered an epidemic in the Americas, the mechanism by which Zika acts is still not comprehensively and wholly understood, and this understanding will be crucial in developing effective vaccines and treatments.

Sequencing of ZIKV genomes directly from Ae. aegypti and Cx. quinquefasciatus mosquitoes collected during the 2015-16 epidemics in Recife

Zika virus (ZIKV) is a negative sense RNA virus from the Flaviviridae family, which was relatively unknown until the first human epidemic in Micronesia, in 2007. Since then, it spread to French Polynesia and the Americas. Recife, the capital of Pernambuco state and epicenter of the Zika epidemic in Brazil, experienced a large number of microcephaly cases and other congenital abnormalities associated to the ZIKV infection from, 2015 to 16. Evidences suggest that both Aedes aegypti and Culex quinquefasciatus mosquitoes from Recife are capable of replicating and transmitting the virus. Here, we conducted high throughput sequencing of ZIKV genomes directly from Ae. aegypti and Cx. quinquefasciatus mosquitoes collected during the ZIKV epidemics in Recife, in order to investigate the variability and evolution of the virus. We obtained 11 draft ZIKV genomes derived from 5 pools from each Ae. aegypti and Cx. quinquefasciatus species. Genome coverage breadth ranged from 16 to 100% and average depth from 45 to 46,584×. Two of these genomes were obtained from pools of Cx. quinquefasciatus females with no sign of blood in the abdomen. Amino acid substitutions found here were not species-specific. In addition, molecular clock dating estimated that ZIKV draft genomes obtained here were co-circulating in other regions of the country during the epidemics. Overall results highlight that viral mutations and even minor variants can be detected in genomes directly sequenced from mosquito samples and insights about natural viral genomic variability and viral evolution can be useful when designing tools for mosquito control programs.

Travel Surveillance and Genomics Uncover a Hidden Zika Outbreak during the Waning Epidemic

The Zika epidemic in the Americas has challenged surveillance and control. As the epidemic appears to be waning, it is unclear whether transmission is still ongoing, which is exacerbated by discrepancies in reporting. To uncover locations with lingering outbreaks, we investigated travel-associated Zika cases to identify transmission not captured by reporting. We uncovered an unreported outbreak in Cuba during 2017, a year after peak transmission in neighboring islands. By sequencing Zika virus, we show that the establishment of the virus was delayed by a year and that the ensuing outbreak was sparked by long-lived lineages of Zika virus from other Caribbean islands. Our data suggest that, although mosquito control in Cuba may initially have been effective at mitigating Zika virus transmission, such measures need to be maintained to be effective. Our study highlights how Zika virus may still be "silently" spreading and provides a framework for understanding outbreak dynamics. VIDEO ABSTRACT.

Vector competence of Aedes aegypti for different strains of Zika virus in Argentina

The importance of Zika virus (ZIKV) has increased noticeably since the outbreak in the Americas in 2015, when the illness was associated with congenital disorders. Although there is evidence of sexual transmission of the virus, the mosquito Aedes aegypti is believed to be the main vector for transmission to humans. This species of mosquito has not only been found naturally infected with ZIKV, but also has been the subject of study in many vector competence assays that employ different strains of ZIKV around the world. In Argentina, the first case was reported in February 2016 and a total of 278 autochthonous cases have since been confirmed, however, ZIKV virus has not been isolated from any mosquito species yet in Argentina. In order to elucidate if Argentinian Ae. aegypti populations could be a possible vector of ZIKV, we conducted vector competence studies that involved a local strain of ZIKV from Chaco province, and a Venezuelan strain obtained from an imported case. For this purpose, Ae. aegypti adults from the temperate area of Argentina (Buenos Aires province) were fed with infected blood. Body, legs and saliva were harvested and tested by plaque titration on plates of Vero cells for ZIKV at 7, 11 and 14 days post infection (DPI) in order to calculate infection, transmission, and dissemination rates, respectively. Both strains were able to infect mosquitoes at all DPIs, whereas dissemination and transmission were observed at all DPIs for the Argentinian strain but only at 14 DPI for the Venezuelan strain. This study proves the ability of Ae. aegypti mosquitoes from Argentina to become infected with two different strains of ZIKV, both belonging to the Asian lineage, and that the virus can disseminate to the legs and salivary glands.

Zika virus is a flavivirus transmitted by mosquitoes, isolated for the first time in the Ziika Forest in Uganda in 1947 from a rhesus macaque monkey. The disease is usually asymptomatic, but sometimes it causes a mild illness that comes with fever, rash, joint pain, and conjunctivitis. The World Health Organization focused the attention on this virus after the outbreak in the Americas, when the virus was linked to microcephaly and serious neurological diseases, including Guillain-Barré syndrome. Aedes aegypti was incriminated as the main vector of the virus as it was found both naturally and experimentally infected. This mosquito species was declared eradicated in Argentina by 1970 but re-emerged in 1989. Recent studies found a peculiarity in the genetics of Argentinian Ae. aegypti populations that consists in a combination between both subspecies: Ae. aegypti formosus and Ae. aegypti aegypti. Our study tries to elucidate if Ae. aegypti from Argentina are able to transmit the virus in order to add these mosquitoes to the list of possible vectors of ZIKV and, in future prospect, orient to fight the virus by controlling the vector.

Molecular Basis for Arbovirus Transmission by Aedes aegypti Mosquitoes

Mosquitoes are considered the most important vectors for the transmission of pathogens to humans. Aedes aegypti is a unique species, not only by its highly anthropophilic and peridomestic habits but also because it can transmit an important variety of pathogenic viruses. Examples are dengue, yellow fever, chikungunya, Zika, and Mayaro viruses. After ingesting viremic blood, a wide range of mechanisms are activated in the mosquito to counteract viral infection. Nevertheless, these arboviruses possess strategies to overcome barriers in the mosquito and eventually reach the salivary glands to continue the transmission cycle. However, the infection and eventual transmission of arbovirus depends on multiple factors. The current review focuses in detail on the anatomic, physiological, and molecular characteristics of the mosquito A. aegypti that participate in response to a viral infection. In the past decades, the awareness of the importance of this mosquito as a disease vector and its impact on human health was largely recognized. We need to improve our comprehension of molecular mechanisms that determine the outcome of successful virus replication or control of infection for each arbovirus in the vector; this could lead to the design of effective control strategies in the future.

Knowledge and perceptions of Zika virus transmission in the community of Puerto Plata, Dominican Republic

Background

Zika virus is associated with increased cases of both microcephaly and Guillain-Barré syndrome. Community knowledge, perceptions and practices to prevent infection with the Zika virus are not well understood, particularly among high risk populations living in resource-poor and Zika-endemic areas. Our objective was to assess knowledge of symptoms, health effects and prevention practices associated with Zika virus in rural communities on the northern coast of the Dominican Republic.

Methods

Study participants were contacted while attending community events such as free medical clinics and invited to be interviewed regarding their knowledge, attitudes, and perceptions of Zika virus using the World Health Organization’s Zika survey tool.

Results

Of the 75 Dominicans that participated, 33% did not know who could become infected with Zika. In addition, only 40% of respondents were able to identify mosquitoes or sexual transmission as the primary routes of infection though 51% of respondents thought that Zika was an important issue in their community.

Conclusions

This study found that general knowledge regarding the basic risks and transmission of Zika were not well understood among a sample of rural Dominicans. Our findings highlight disparities in knowledge and perception of risk from Zika in rural areas compared to previous studies conducted in the Dominican Republic. Education about the basic risks and transmission of Zika are critically needed in these remote populations to reduce Zika transmission.

Vector competence of Australian Aedes aegypti and Aedes albopictus for an epidemic strain of Zika virus

BACKGROUND

Recent epidemics of Zika virus (ZIKV) in the Pacific and the Americas have highlighted its potential as an emerging pathogen of global importance. Both Aedes (Ae.) aegypti and Ae. albopictus are known to transmit ZIKV but variable vector competence has been observed between mosquito populations from different geographical regions and different virus strains. Since Australia remains at risk of ZIKV introduction, we evaluated the vector competence of local Ae. aegypti and Ae. albopictus for a Brazilian epidemic ZIKV strain. In addition, we evaluated the impact of daily temperature fluctuations around a mean of 28°C on ZIKV transmission and extrinsic incubation period.

METHODOLOGY/PRINCIPAL FINDINGS

Mosquitoes were orally challenged with a Brazilian ZIKV strain (8.8 log CCID50/ml) and maintained at either 28°C constant or fluctuating temperature conditions. At 3, 7 and 14 days post-infection (dpi), ZIKV RNA copies were quantified in mosquito bodies, as well as wings and legs, using qRT-PCR, while virus antigen in saliva (a proxy for transmission) was detected using a cell culture ELISA. Despite high body and disseminated infection rates in both vectors, the transmission rates of ZIKV in saliva of Ae. aegypti (50-60%) were significantly higher than in Ae. albopictus (10%) at 14 dpi. Both species supported a high viral load in bodies, with no significant differences between constant and fluctuating temperature conditions. However, a significant difference in viral load in wings and legs between species was observed, with higher titres in Ae. aegypti maintained at constant temperature conditions. For ZIKV transmission to occur in Ae. aegypti, a disseminated virus load threshold of 7.59 log10 copies had to be reached.

CONCLUSIONS/SIGNIFICANCE

Australian Ae. aegypti are better able to transmit a Brazilian ZIKV strain than Ae. albopictus. The results are in agreement with the global consensus that Ae. aegypti is the major vector of ZIKV.

Arbovirus coinfection and co-transmission: A neglected public health concern?

Epidemiological synergy between outbreaks of viruses transmitted by Aedes aegypti mosquitoes, such as chikungunya, dengue, and Zika viruses, has resulted in coinfection of humans with multiple viruses. Despite the potential impact on public health, we know only little about the occurrence and consequences of such coinfections. Here, we review the impact of coinfection on clinical disease in humans, discuss the possibility for co-transmission from mosquito to human, and describe a role for modeling transmission dynamics at various levels of co-transmission. Solving the mystery of virus coinfections will reveal whether they should be viewed as a serious concern for public health.