A mosquito salivary protein-driven influx of myeloid cells facilitates flavivirus transmission

Mosquitoes transmit many disease-relevant flaviviruses. Efficient viral transmission to mammalian hosts requires mosquito salivary factors. However, the specific salivary components facilitating viral transmission and their mechanisms of action remain largely unknown. Here, we show that a female mosquito salivary gland-specific protein, here named A. aegypti Neutrophil Recruitment Protein (AaNRP), facilitates the transmission of Zika and dengue viruses. AaNRP promotes a rapid influx of neutrophils, followed by virus-susceptible myeloid cells toward mosquito bite sites, which facilitates establishment of local infection and systemic dissemination. Mechanistically, AaNRP engages TLR1 and TLR4 of skin-resident macrophages and activates MyD88-dependent NF-κB signaling to induce the expression of neutrophil chemoattractants. Inhibition of MyD88-NF-κB signaling with the dietary phytochemical resveratrol reduces AaNRP-mediated enhancement of flavivirus transmission by mosquitoes. These findings exemplify how salivary components can aid viral transmission, and suggest a potential prophylactic target.

Optimising the surveillance of Aedes aegypti in Brazil by selecting smaller representative areas within an endemic city

OBJECTIVES

Arboviruses, such as dengue (DENV), zika (ZIKV), and chikungunya (CHIKV), constitute a growing urban public health threat. Focusing on Aedes aegypti mosquitoes, their primary vectors, is crucial for mitigation. While traditional immature-stage mosquito surveillance has limitations, capturing adult mosquitoes through traps yields more accurate data on disease transmission. However, deploying traps presents logistical and financial challenges, demonstrating effective temporal predictions but lacking spatial accuracy. Our goal is to identify smaller representative areas within cities to enhance the early warning system for DENV outbreaks.

METHODS

We created Sentinel Geographic Units (SGUs), smaller areas of 1 km2 within each stratum, larger areas, with the aim of aligning the Trap Positivity Index (TPI) and Adult Density Index (ADI) with their respective strata. We conducted a two-step evaluation of SGUs. First, we examined the equivalence of TPI and ADI between SGUs and strata from January 2017 to July 2022. Second, we assessed the ability of SGU's TPI and ADI to predict DENV outbreaks in comparison to Foz do Iguaçu's Early-Warning System, which forecasts outbreaks up to 4 weeks ahead. Spatial and temporal analyses were carried out, including data interpolation and model selection based on Akaike information criteria (AIC).

RESULTS

Entomological indicators produced in small SGUs can effectively replace larger sentinel areas to access dengue outbreaks. Based on historical data, the best predictive capability is achieved 2 weeks after infestation verification. Implementing the SGU strategy with more frequent sampling can provide more precise space-time estimates and enhance dengue control.

CONCLUSIONS

The implementation of SGUs offers an efficient way to monitor mosquito populations, reducing the need for extensive resources. This approach has the potential to improve dengue transmission management and enhance the public health response in endemic cities.

Zika emergence, persistence, and transmission rate in Colombia: a nationwide application of a space-time Markov switching model

Zika, a viral disease transmitted to humans by Aedes mosquitoes, emerged in the Americas in 2015, causing large-scale epidemics. Colombia alone reported over 72,000 Zika cases between 2015 and 2016. Using national surveillance data from 1121 municipalities over 70 weeks, we identified sociodemographic and environmental factors associated with Zika's emergence, re-emergence, persistence, and transmission intensity in Colombia. We fitted a zero-state Markov-switching model under the Bayesian framework, assuming Zika switched between periods of presence and absence according to spatially and temporally varying probabilities of emergence/re-emergence (from absence to presence) and persistence (from presence to presence). These probabilities were assumed to follow a series of mixed multiple logistic regressions. When Zika was present, assuming that the cases follow a negative binomial distribution, we estimated the transmission intensity rate. Our results indicate that Zika emerged/re-emerged sooner and that transmission was intensified in municipalities that were more densely populated, at lower altitudes and/or with less vegetation cover. Warmer temperatures and less weekly-accumulated rain were also associated with Zika emergence. Zika cases persisted for longer in more densely populated areas with more cases reported in the previous week. Overall, population density, elevation, and temperature were identified as the main contributors to the first Zika epidemic in Colombia. We also estimated the probability of Zika presence by municipality and week, and the results suggest that the disease circulated undetected by the surveillance system on many occasions. Our results offer insights into priority areas for public health interventions against emerging and re-emerging Aedes-borne diseases.

A naturally isolated symbiotic bacterium suppresses flavivirus transmission by Aedes mosquitoes

The commensal microbiota of the mosquito gut plays a complex role in determining the vector competence for arboviruses. In this study, we identified a bacterium from the gut of field Aedes albopictus mosquitoes named Rosenbergiella sp. YN46 (Rosenbergiella_YN46) that rendered mosquitoes refractory to infection with dengue and Zika viruses. Inoculation of 1.6 × 103 colony forming units (CFUs) of Rosenbergiella_YN46 into A. albopictus mosquitoes effectively prevents viral infection. Mechanistically, this bacterium secretes glucose dehydrogenase (RyGDH), which acidifies the gut lumen of fed mosquitoes, causing irreversible conformational changes in the flavivirus envelope protein that prevent viral entry into cells. In semifield conditions, Rosenbergiella_YN46 exhibits effective transstadial transmission in field mosquitoes, which blocks transmission of dengue virus by newly emerged adult mosquitoes. The prevalence of Rosenbergiella_YN46 is greater in mosquitoes from low-dengue areas (52.9 to ~91.7%) than in those from dengue-endemic regions (0 to ~6.7%). Rosenbergiella_YN46 may offer an effective and safe lead for flavivirus biocontrol.

Gain without pain: adaptation and increased virulence of Zika virus in vertebrate host without fitness cost in mosquito vector

IMPORTANCE

Previously, we modeled direct transmission chains of Zika virus (ZIKV) by serially passaging ZIKV in mice and mosquitoes and found that direct mouse transmission chains selected for viruses with increased virulence in mice and the acquisition of non-synonymous amino acid substitutions. Here, we show that these same mouse-passaged viruses also maintain fitness and transmission capacity in mosquitoes. We used infectious clone-derived viruses to demonstrate that the substitution in nonstructural protein 4A contributes to increased virulence in mice.

A metapopulation approach to identify targets for Wolbachia-based dengue control

Over the last decade, the release of Wolbachia-infected Aedes aegypti into the natural habitat of this mosquito species has become the most sustainable and long-lasting technique to prevent and control vector-borne diseases, such as dengue, zika, or chikungunya. However, the limited resources to generate such mosquitoes and their effective distribution in large areas dominated by the Aedes aegypti vector represent a challenge for policymakers. Here, we introduce a mathematical framework for the spread of dengue in which competition between wild and Wolbachia-infected mosquitoes, the cross-contagion patterns between humans and vectors, the heterogeneous distribution of the human population in different areas, and the mobility flows between them are combined. Our framework allows us to identify the most effective areas for the release of Wolbachia-infected mosquitoes to achieve a large decrease in the global dengue prevalence.

Zika Virus Infection of Sertoli Cells Alters Protein Expression Involved in Activated Immune and Antiviral Response Pathways, Carbohydrate Metabolism and Cardiovascular Disease

Zika virus (ZIKV), a re-emerging virus, causes congenital brain abnormalities and Guillain–Barré syndrome. It is mainly transmitted by Aedes mosquitoes, but infections are also linked to sexual transmissions. Infectious ZIKV has been isolated, and viral RNA has been detected in semen over a year after the onset of initial symptoms, but the mode of long-term persistence is not yet understood. ZIKV can proliferate in human Sertoli cells (HSerC) for several weeks in vitro, suggesting that it might be a reservoir for persistent ZIKV infection. This study determined proteomic changes in HSerC during ZIKV infections by TMT-mass spectrometry analysis. Levels of 4416 unique Sertoli cell proteins were significantly altered at 3, 5, and 7 days after ZIKV infection. The significantly altered proteins include enzymes, transcription regulators, transporters, kinases, peptidases, transmembrane receptors, cytokines, ion channels, and growth factors. Many of these proteins are involved in pathways associated with antiviral response, antigen presentation, and immune cell activation. Several immune response pathway proteins were significantly activated during infection, e.g., interferon signaling, T cell receptor signaling, IL-8 signaling, and Th1 signaling. The altered protein levels were linked to predicted activation of immune response in HSerC, which was predicted to suppress ZIKV infection. ZIKV infection also affected the levels of critical regulators of gluconeogenesis and glycolysis pathways such as phosphoglycerate mutase, phosphoglycerate kinase, and enolase. Interestingly, many significantly altered proteins were associated with cardiac hypertrophy, which may induce heart failure in infected patients. In summary, our research contributes to a better understanding of ZIKV replication dynamics and infection in Sertoli cells.

Using Sina-Weibo microblogs to inform the development and dissemination of health awareness material about Zika virus transmission, China, 2016–17

Background

On 1 February 2016, the World Health Organization declared Zika transmission a public health emergency of international concern. Monitoring and responding to community awareness, concern, and possible knowledge gaps are critical during public health emergencies. Here, we describe the review and analysis of micro-blogs posted on Sina-Weibo, China’s largest social media platform, to develop and disseminate a Zika virus education campaign.

Methods

We used CYYUN Voice Express’ Weibo Spider tool and the search terms of "Zhaika" OR "Zika" OR "Zikv” to capture microblogs about Zika virus retrospectively from February 1 to December 31, 2016 and prospectively from June 1 to November 15, 2017. We described microblogs meeting our inclusion criteria by month and Zika virus outbreaks in Asia and by source (e.g., government agency, individual, or other). We identified common misleading or inaccurate content authored by individual micro-bloggers (i.e., not supported by available scientific evidence) through a qualitative review. We used this information to develop and disseminate health awareness material about the Zika virus through China CDC’s 12320 Health Hotline Weibo account. An online survey was conducted to obtain feedback on the material.

Results

We captured 15,888 microblogs meeting our inclusion criteria. Zika-related microblogs peaked in September 2016, corresponding to news reports about the Zika outbreak in Singapore (August to November 2016). Most microblogs (12,994 [82%]) were authored by individual users, followed by media agencies (842 [5%]), businesses (829 [5%]), international organizations (370 [2%]), and Chinese government agencies (235 [1%]). Relevant microblogs primarily focused on clinical symptoms and health risks, modes of transmission, and actions taken by individuals to prevent infection and seek health care. Incorrect and/or mis-leading information from individual users concentrated on modes of transmission and possible treatments. The microblog "#Zika is that far and this close" health campaign was posted on Sina-Weibo and Baidu (Internet search engine in China) on September 18, 2016. Younger respondents (p-value = 0.01), and those with at least a college education (p-value = 0.03), were more likely than other respondents to consider the online campaign reliable and trustworthy.

Conclusion

Routine review of Sina-Weibo and other social media platforms could enhance the ability of public health staff to effectively respond to community concerns and awareness during public health emergencies. Advancements of social media monitoring tools and staff training could help to promote health awareness during emergencies by directly addressing public perceptions and concerns. Various approaches may be needed to reach different at-risk populations, particularly older and less educated populations who may prefer more traditional modes of communication.

First Report of Adult Aedes aegypti (Diptera: Culicidae) Resistance to Pyrethroids in Argentina

Severe human arboviral diseases can be transmitted by the mosquito Aedes aegypti (Linnaeus), including dengue, chikungunya, Zika, and yellow fever. Adult control using spatial sprays with adulticides is recommended only when dengue outbreaks occur. In Argentina, mainly pyrethroids, like cis-permethrin, have been used as an adulticide, especially since 2008. The evolution and spread of resistance to insecticides is a major concern for vector control. This study reports for the first time pyrethroid resistance in Ae. aegypti adults from Argentina, in the city of Salvador Mazza (Salta). WHO discriminating doses of 0.75% were used for permethrin, 0.05% for deltamethrin, and 5% for malathion. Also the discriminating dose for cis-permethrin (0.6%) was calculated and evaluated for the first time. We found a resistance ratio 50 (RR50) of 10.3 (9.7-10.4) for cis-permethrin, which is considered as high resistance. Our results also indicated resistance to deltamethrin (22.6% mortality) and permethrin (53.6% mortality), and a total susceptibility to malathion (100% mortality). Results from this study highlight the importance of the correct use of insecticides within an Integrated Vector Management (IVM) approach and of early detection of resistance to enable Ae. aegypti control in Argentina. More studies are needed to determine the spread of mosquito resistance to pyrethroids.

Deciphering the Role of Extracellular Vesicles Derived from ZIKV-Infected hcMEC/D3 Cells on the Blood-Brain Barrier System

To date, no vaccines or antivirals are available against Zika virus (ZIKV). In addition, the mechanisms underlying ZIKV-associated pathogenesis of the central nervous system (CNS) are largely unexplored. Getting more insight into the cellular pathways that ZIKV recruits to facilitate infection of susceptible cells will be crucial for establishing an effective treatment strategy. In general, cells secrete a number of vesicles, known as extracellular vesicles (EVs), in response to viral infections. These EVs serve as intercellular communicators. Here, we investigated the role of EVs derived from ZIKV-infected human brain microvascular endothelial cells on the blood–brain barrier (BBB) system. We demonstrated that ZIKV-infected EVs (IEVs) can incorporate viral components, including ZIKV RNA, NS1, and E-protein, and further transfer them to several types of CNS cells. Using label-free impedance-based biosensing, we observed that ZIKV and IEVs can temporally disturb the monolayer integrity of BBB-mimicking cells, possibly by inducing structural rearrangements of the adherent protein VE-cadherin (immunofluorescence staining). Finally, differences in the lipidomic profile between EVs and their parental cells possibly suggest a preferential sorting mechanism of specific lipid species into the vesicles. To conclude, these data suggest that IEVs could be postulated as vehicles (Trojan horse) for ZIKV transmission via the BBB.

Zika virus and temperature modulate Elizabethkingia anophelis in Aedes albopictus

BACKGROUND

Vector-borne pathogens must survive and replicate in the hostile environment of an insect's midgut before successful dissemination. Midgut microbiota interfere with pathogen infection by activating the basal immunity of the mosquito and by synthesizing pathogen-inhibitory metabolites.

METHODS

The goal of this study was to assess the influence of Zika virus (ZIKV) infection and increased temperature on Aedes albopictus midgut microbiota. Aedes albopictus were reared at diurnal temperatures of day 28 °C/night 24 °C (L) or day 30 °C/night 26 °C (M). The mosquitoes were given infectious blood meals with 2.0 × 108 PFU/ml ZIKV, and 16S rRNA sequencing was performed on midguts at 7 days post-infectious blood meal exposure.

RESULTS

Our findings demonstrate that Elizabethkingia anophelis albopictus was associated with Ae. albopictus midguts exposed to ZIKV infectious blood meal. We observed a negative correlation between ZIKV and E. anophelis albopictus in the midguts of Ae. albopictus. Supplemental feeding of Ae. albopictus with E. anophelis aegypti and ZIKV resulted in reduced ZIKV infection rates. Reduced viral loads were detected in Vero cells that were sequentially infected with E. anophelis aegypti and ZIKV, dengue virus (DENV), or chikungunya virus (CHIKV).

CONCLUSIONS

Our findings demonstrate the influence of ZIKV infection and temperature on the Ae. albopictus microbiome along with a negative correlation between ZIKV and E. anophelis albopictus. Our results have important implications for controlling vector-borne pathogens.

Impact of extrinsic incubation temperature on natural selection during Zika virus infection of Aedes aegypti and Aedes albopictus

Arthropod-borne viruses (arboviruses) require replication across a wide range of temperatures to perpetuate. While vertebrate hosts tend to maintain temperatures of approximately 37°C—40°C, arthropods are subject to ambient temperatures which can have a daily fluctuation of > 10°C. Temperatures impact vector competence, extrinsic incubation period, and mosquito survival unimodally, with optimal conditions occurring at some intermediate temperature. In addition, the mean and range of daily temperature fluctuations influence arbovirus perpetuation and vector competence. The impact of temperature on arbovirus genetic diversity during systemic mosquito infection, however, is poorly understood. Therefore, we determined how constant extrinsic incubation temperatures of 25°C, 28°C, 32°C, and 35°C control Zika virus (ZIKV) vector competence and population dynamics within Aedes aegypti and Aedes albopictus mosquitoes. We also examined fluctuating temperatures which better mimic field conditions in the tropics. We found that vector competence varied in a unimodal manner for constant temperatures peaking between 28°C and 32°C for both Aedes species. Transmission peaked at 10 days post-infection for Aedes aegypti and 14 days for Aedes albopictus. Conversely, fluctuating temperature decreased vector competence. Using RNA-seq to characterize ZIKV population structure, we identified that temperature alters the selective environment in unexpected ways. During mosquito infection, constant temperatures more often elicited positive selection whereas fluctuating temperatures led to strong purifying selection in both Aedes species. These findings demonstrate that temperature has multiple impacts on ZIKV biology, including major effects on the selective environment within mosquitoes.

Arthropod-borne viruses (arboviruses) have emerged in recent decades due to complex factors that include increases in international travel and trade, the breakdown of public health infrastructure, land use changes, and many others. Climate change also has the potential to shift the geographical ranges of arthropod vectors, consequently increasing the global risk of arbovirus infection. Changing temperatures may alter the virus-host interaction, ultimately resulting in the emergence of new viruses and virus genotypes in new areas. Therefore, we sought to characterize how temperature (both constant and fluctuating) alters the ability of Aedes aegypti and Aedes albopictus to transmit Zika virus, and how it influences virus populations within mosquitoes. We found that intermediate temperatures maximize virus transmission compared to more extreme and fluctuating temperatures. Constant temperatures increased positive selection on virus genomes, while fluctuating temperatures strengthened purifying selection. Our studies provide evidence that in addition to altering vector competence, temperature significantly influences natural selection within mosquitoes.

From Mosquito Bites to Sexual Transmission: Evaluating Mouse Models of Zika Virus Infection

Following the recent outbreak of Zika virus (ZIKV) infections in Latin America, ZIKV has emerged as a global health threat due to its ability to induce neurological disease in both adults and the developing fetus. ZIKV is largely mosquito-borne and is now endemic in many parts of Africa, Asia, and South America. However, several reports have demonstrated persistent ZIKV infection of the male reproductive tract and evidence of male-to-female sexual transmission of ZIKV. Sexual transmission may broaden the reach of ZIKV infections beyond its current geographical limits, presenting a significant threat worldwide. Several mouse models of ZIKV infection have been developed to investigate ZIKV pathogenesis and develop effective vaccines and therapeutics. However, the majority of these models focus on mosquito-borne infection, while few have considered the impact of sexual transmission on immunity and pathogenesis. This review will examine the advantages and disadvantages of current models of mosquito-borne and sexually transmitted ZIKV and provide recommendations for the effective use of ZIKV mouse models.

Dengue and Zika virus infection patterns vary among Aedes aegypti field populations from Belo Horizonte, a Brazilian endemic city

Dengue virus (DENV) and Zika virus (ZIKV) belong to the same viral family, the Flaviviridae. They cause recurring threats to the public health systems of tropical countries such as Brazil. The primary Brazilian vector of both viruses is the mosquito Aedes aegypti. After the mosquito ingests a blood meal from an infected person, the viruses infect and replicate in the midgut, disseminate to secondary tissues and reach the salivary gland (SG), where they are ready to be transmitted to a vertebrate host. It is thought that the intrinsic discrepancies among mosquitoes could affect their ability to deal with viral infections. This study confirms that the DENV and ZIKV infection patterns of nine Ae. aegypti field populations found in geographically separate health districts of an endemic Brazilian city vary. We analyzed the infection rate, disseminated infection, vector competence, and viral load through quantitative PCR. Mosquitoes were challenged using the membrane-feeding assay technique and were tested seven and fourteen days post-infection (early and late infection phases, respectively). The infection responses varied among the Ae. aegypti populations for both flaviviruses in the two infection phases. There was no similarity between DENV and ZIKV vector competencies or viral loads. According to the results of our study, the risk of viral transmission overtime after infection either increases or remains unaltered in ZIKV infected vectors. However, the risk may increase, decrease, or remain unaltered in DENV-infected vectors depending on the mosquito population. For both flaviviruses, the viral load persisted in the body even until the late infection phase. In contrast to DENV, the ZIKV accumulated in the SG over time in all the mosquito populations. These findings are novel and may help direct the development of control strategies to fight dengue and Zika outbreaks in endemic regions, and provide a warning about the importance of understanding mosquito responses to arboviral infections.

Dengue and Zika are neglected diseases caused by viruses transmitted to humans by mosquitoes (vector-borne diseases). The primary vector of both diseases is Aedes aegypti, a highly abundant mosquito in tropical countries and adapted to the urban habitat. The viral cycle in the vector starts when the mosquito bites an infected person and acquires the viruses through the blood meal. When the infected blood reaches the mosquito’s midgut, the viruses invade the epithelial cells and disseminate in several organs until they reach the salivary glands, enabling viral transmission to the next person. However, the mosquitoes have developed strategies to combat the viral invasion and dissemination in their body, making this journey a challenge to the viruses. Herein, we show that the mosquito responses against dengue and Zika viruses are distinct. In addition, mosquitoes from separate populations of the same city have different abilities to deal with the viruses in both cases, dengue and Zika infections. Our results show the diversity of responses that the mosquitoes may present to viral infections. These findings may better direct disease control strategies to combat dengue and Zika outbreaks in endemic regions.

Viral genome-based Zika virus transmission dynamics in a paediatric cohort during the 2016 Nicaragua epidemic

BACKGROUND

Nicaragua experienced a large Zika epidemic in 2016, with up to 50% of the population in Managua infected. With the domesticated Aedes aegypti mosquito as its vector, it is widely assumed that Zika virus transmission occurs within the household and/or via human mobility. We investigated these assumptions by using viral genomes to trace Zika transmission spatially.

METHODS

We analysed serum samples from 119 paediatric Zika cases participating in the long-standing Paediatric Dengue Cohort Study in Managua, which was expanded to include Zika in 2015. An optimal spanning directed tree was constructed by minimizing the differences in viral sequence diversity composition between patient nodes, where low-frequency variants were used to increase the resolution of the inferred Zika outbreak dynamics.

FINDINGS

Out of the 18 houses where pairwise difference in sample collection dates among all the household members was within 30 days, we only found two where viruses from individuals within the same household were up to 10th-most closely linked to each other genetically. We also identified a substantial number of transmission events involving long geographical distances (n=30), as well as potential super-spreading events in the estimated transmission tree.

INTERPRETATION

Our finding highlights that community transmission, often involving long geographical distances, played a much more important role in epidemic spread than within-household transmission.

FUNDING

This study was supported by an NUS startup grant (OMS) and grants R01 AI099631 (AB), P01 AI106695 (EH), P01 AI106695-03S1 (FB), and U19 AI118610 (EH) from the US National Institutes of Health.

Susceptibility and interactions between Aedes mosquitoes and Zika viruses

Zika virus disease is caused by Zika virus infection, as transmitted by Aedes spp. mosquitoes. Many of the Zika virus strains isolated from patients display different pathogenicities toward humans. The vector mosquitoes for Zika virus are mainly of the Aedes genus, especially Aedes aegypti and Aedes albopictus. However, susceptibility and interactions between Aedes spp. mosquitoes and Zika viruses remain unclear. In this study, we chose two Zika virus strains (FSS13025 and PRVABC59) with different abilities to infect the primary vector mosquitoes Ae. aegypti and Ae. albopictus. The transcriptomes and small RNA profiles of infected and uninfected mosquitoes were comparatively analyzed, and differentially expressed genes were functionally examined using RNA interference. According to the results, the susceptibility of PRVABC59 was higher than that of FSS13025 in Aedes vector mosquitoes, and Ae. aegypti was more susceptible to Zika virus than was Ae. albopictus. For PRVABC59 infection, specific differential expression profiles correlated with Ae. aegypti and Ae. albopictus, and susceptibility was significantly affected when three targeted genes were successfully knocked down. Compared with PRVABC59, infection of Ae. albopictus with FSS13025 generated more 21-nt virus small interference RNA. It can be concluded that the susceptibility of vector Aedes spp. mosquitoes to Zika viruses varies and that the interactions between mosquitoes and Zika virus correlate with susceptibility.

Influence of Pyrethroid Resistance on Vector Competency for Zika Virus by Aedes aegypti (Diptera: Culicidae)

The vector competence of mosquitoes for pathogens has been shown to be influenced by the status of insecticide resistance in the mosquito population. However, to date, only two studies has explored the impact of insecticide resistance on arbovirus transmission. The global and widespread use of pyrethroids has led to the development of insecticide resistance in many mosquito species, including Aedes aegypti (Linnaeus) (Diptera: Culicidae), the primary vector of Zika virus. Strains of Ae. aegypti that were genetically similar, but responded differently to pyrethroid exposure, were developed using backcrossing techniques. These populations were orally infected with Zika virus and susceptibility to infection, disseminated infection, and transmission potential were evaluated. Analyses revealed differences in susceptibility to infection and disseminated infection between the pyrethroid susceptible and resistant strains of Ae. aegypti during the infection period. Here, we identify an additional challenge to that of widespread pyrethroid resistance. Specifically, resistance is associated with altered phenotypic traits that influence susceptibility to arbovirus infection and progression of infection in the mosquito, factors which ultimately influence risk of arbovirus transmission. These findings support the need to 1) consider insecticide resistance status during times of arbovirus transmission and 2) to implement insecticide resistance management/ mitigation strategies in vector control programs.

Mother-to-Child Transmission of Arboviruses during Breastfeeding: From Epidemiology to Cellular Mechanisms

Most viruses use several entry sites and modes of transmission to infect their host (parenteral, sexual, respiratory, oro-fecal, transplacental, transcutaneous, etc.). Some of them are known to be essentially transmitted via arthropod bites (mosquitoes, ticks, phlebotomes, sandflies, etc.), and are thus named arthropod-borne viruses, or arboviruses. During the last decades, several arboviruses have emerged or re-emerged in different countries in the form of notable outbreaks, resulting in a growing interest from scientific and medical communities as well as an increase in epidemiological studies. These studies have highlighted the existence of other modes of transmission. Among them, mother-to-child transmission (MTCT) during breastfeeding was highlighted for the vaccine strain of yellow fever virus (YFV) and Zika virus (ZIKV), and suggested for other arboviruses such as Chikungunya virus (CHIKV), dengue virus (DENV), and West Nile virus (WNV). In this review, we summarize all epidemiological and clinical clues that suggest the existence of breastfeeding as a neglected route for MTCT of arboviruses and we decipher some of the mechanisms that chronologically occur during MTCT via breastfeeding by focusing on ZIKV transmission process.

Effectiveness of Wolbachia-infected mosquito deployments in reducing the incidence of dengue and other Aedes-borne diseases in Niterói, Brazil: A quasi-experimental study

BACKGROUND

The introduction of the bacterium Wolbachia (wMel strain) into Aedes aegypti mosquitoes reduces their capacity to transmit dengue and other arboviruses. Evidence of a reduction in dengue case incidence following field releases of wMel-infected Ae. aegypti has been reported previously from a cluster randomised controlled trial in Indonesia, and quasi-experimental studies in Indonesia and northern Australia.

METHODOLOGY/PRINCIPAL FINDINGS

Following pilot releases in 2015-2016 and a period of intensive community engagement, deployments of adult wMel-infected Ae. aegypti mosquitoes were conducted in Niterói, Brazil during 2017-2019. Deployments were phased across four release zones, with a total area of 83 km2 and a residential population of approximately 373,000. A quasi-experimental design was used to evaluate the effectiveness of wMel deployments in reducing dengue, chikungunya and Zika incidence. An untreated control zone was pre-defined, which was comparable to the intervention area in historical dengue trends. The wMel intervention effect was estimated by controlled interrupted time series analysis of monthly dengue, chikungunya and Zika case notifications to the public health surveillance system before, during and after releases, from release zones and the control zone. Three years after commencement of releases, wMel introgression into local Ae. aegypti populations was heterogeneous throughout Niterói, reaching a high prevalence (>80%) in the earliest release zone, and more moderate levels (prevalence 40-70%) elsewhere. Despite this spatial heterogeneity in entomological outcomes, the wMel intervention was associated with a 69% reduction in dengue incidence (95% confidence interval 54%, 79%), a 56% reduction in chikungunya incidence (95%CI 16%, 77%) and a 37% reduction in Zika incidence (95%CI 1%, 60%), in the aggregate release area compared with the pre-defined control area. This significant intervention effect on dengue was replicated across all four release zones, and in three of four zones for chikungunya, though not in individual release zones for Zika.

CONCLUSIONS/SIGNIFICANCE

We demonstrate that wMel Wolbachia can be successfully introgressed into Ae. aegypti populations in a large and complex urban setting, and that a significant public health benefit from reduced incidence of Aedes-borne disease accrues even where the prevalence of wMel in local mosquito populations is moderate and spatially heterogeneous. These findings are consistent with the results of randomised and non-randomised field trials in Indonesia and northern Australia, and are supportive of the Wolbachia biocontrol method as a multivalent intervention against dengue, chikungunya and Zika.

Transmission Potential of Zika Virus by Aedes aegypti (Diptera: Culicidae) and Ae. mediovittatus (Diptera: Culicidae) Populations From Puerto Rico

Recurrence of local transmission of Zika virus in Puerto Rico is a major public health risk to the United States, where mosquitoes Aedes aegypti (Linnaeus) and Aedes mediovittatus (Coquillett) are abundant. To determine the extent to which Ae. mediovittatus are capable of transmitting Zika virus and the influence of viremia, we evaluated infection and transmission in Ae. mediovittatus and Ae. aegypti from Puerto Rico using serial dilutions of infectious blood. Higher doses of infectious blood resulted in greater infection rates in both mosquitoes. Aedes aegypti females were up to twice as susceptible to infection than Ae. mediovittatus, indicating a more effective midgut infection barrier in the latter mosquito species. Aedes aegypti exhibited higher disseminated infection (40-95%) than Ae. mediovittatus (<5%), suggesting a substantial midgut escape barrier in Ae. mediovittatus. For Ae. aegypti, transmission rates were low over a range of doses of Zika virus ingested, suggesting substantial salivary gland barriers.

Mosquito-Associated Viruses and Their Related Mosquitoes in West Africa

Mosquito-associated viruses (MAVs), including mosquito-specific viruses (MSVs) and mosquito-borne (arbo)viruses (MBVs), are an increasing public, veterinary, and global health concern, and West Africa is projected to be the next front for arboviral diseases. As in-depth knowledge of the ecologies of both western African MAVs and related mosquitoes is still limited, we review available and comprehensive data on their diversity, abundance, and distribution. Data on MAVs’ occurrence and related mosquitoes were extracted from peer-reviewed publications. Data on MSVs, and mosquito and vertebrate host ranges are sparse. However, more data are available on MBVs (i.e., dengue, yellow fever, chikungunya, Zika, and Rift Valley fever viruses), detected in wild and domestic animals, and humans, with infections more concentrated in urban areas and areas affected by strong anthropogenic changes. Aedes aegypti, Culex quinquefasciatus, and Aedes albopictus are incriminated as key arbovirus vectors. These findings outline MAV, related mosquitoes, key knowledge gaps, and future research areas. Additionally, these data highlight the need to increase our understanding of MAVs and their impact on host mosquito ecology, to improve our knowledge of arbovirus transmission, and to develop specific strategies and capacities for arboviral disease surveillance, diagnostic, prevention, control, and outbreak responses in West Africa.

Spatiotemporal Heterogeneity of Zika Virus Transmission in Indonesia: Serosurveillance Data from a Pediatric Population

The presence of Zika virus (ZIKV) in Indonesia has been recognized since the 1970s, but its transmission dynamics there have been poorly understood. To understand more fully the geographic distribution and burden of ZIKV infection, we performed retrospective serological tests on specimens collected from asymptomatic children age 5 to 9 years old living at 30 sites in 14 provinces. Of 870 serum samples tested, 9.2% were found to be positive for anti-ZIKV antibodies, as confirmed by plaque reduction neutralization assays. This was the same overall prevalence reported previously for 1- to 4-year-old children collected at the same sites at the same time. Together with geographic differences in seroprevalence between the age groups, these data suggest that, although ZIKV might be endemic in Indonesia, its occurrence has been focal and episodic.

Plasma lipidome profiling of newborns with antenatal exposure to Zika virus

The 2015–2016 Zika virus (ZIKV) outbreak in Brazil was remarkably linked to the incidence of microcephaly and other deleterious clinical manifestations, including eye abnormalities, in newborns. It is known that ZIKV targets the placenta, triggering an inflammatory profile that may cause placental insufficiency. Transplacental lipid transport is delicately regulated during pregnancy and deficiency on the delivery of lipids such as arachidonic and docosahexaenoic acids may lead to deficits in both brain and retina during fetal development. Here, plasma lipidome profiles of ZIKV exposed microcephalic and normocephalic newborns were compared to non-infected controls. Our results reveal major alterations in circulating lipids from both ZIKV exposed newborns with and without microcephaly relative to controls. In newborns with microcephaly, the plasma concentrations of hydroxyoctadecadienoic acid (HODE), primarily as 13-HODE isomer, derived from linoleic acid were higher as compared to normocephalic ZIKV exposed newborns and controls. Total HODE concentrations were also positively associated with levels of other oxidized lipids and several circulating free fatty acids in newborns, indicating a possible plasma lipidome signature of microcephaly. Moreover, higher concentrations of lysophosphatidylcholine in ZIKV exposed normocephalic newborns relative to controls suggest a potential disruption of polyunsaturated fatty acids transport across the blood-brain barrier of fetuses. The latter data is particularly important given the neurocognitive and neurodevelopmental abnormalities observed in follow-up studies involving children with antenatal ZIKV exposure, but normocephalic at birth. Taken together, our data reveal that plasma lipidome alterations associated with antenatal exposure to ZIKV could contribute to identification and monitoring of the wide spectrum of clinical phenotypes at birth and further, during childhood.

Antenatal exposure to Zika virus (ZIKV) is linked to a wide range of clinical presentations at birth, from asymptomatic cases to microcephaly, and other neurocognitive and neurodevelopmental abnormalities manifested in the early childhood. Stratification of these clinical phenotypes in newborns with suspected antenatal ZIKV exposure is challenging, but critical to improve early assessment of rehabilitative interventions. In this study, plasma lipidome profiling of 274 lipid species was performed in both normocephalic and microcephalic newborns with antenatal ZIKV exposure and compared to non-infected controls. Multiple lipid species were independent predictors of antenatal ZIKV exposure. More specifically, microcephaly was strongly associated with an oxidized free fatty acid and ZIKV exposed normocephalic newborns exhibited higher plasma concentrations of lysophosphatidylcholine relative to controls. These findings emphasize the need for studies focused on the role of individual lipids in neuropathogenesis of ZIKV and raise the potential of plasma lipidome profiling for early diagnosis of newborns with suspected antenatal ZIKV exposure. To validate the predictive ability of this approach, prospective studies with a larger cohort of newborns are now required.

Epididymal epithelium propels early sexual transmission of Zika virus in the absence of interferon signaling

Recognition of Zika virus (ZIKV) sexual transmission (ST) among humans challenges our understanding of the maintenance of mosquito-borne viruses in nature. Here we dissected the relative contributions of the components of male reproductive system (MRS) during early male-to-female ZIKV transmission by utilizing mice with altered antiviral responses, in which ZIKV is provided an equal opportunity to be seeded in the MRS tissues. Using microRNA-targeted ZIKV clones engineered to abolish viral infectivity to different parts of the MRS or a library of ZIKV genomes with unique molecular identifiers, we pinpoint epithelial cells of the epididymis (rather than cells of the testis, vas deferens, prostate, or seminal vesicles) as a most likely source of the sexually transmitted ZIKV genomes during the early (most productive) phase of ZIKV shedding into the semen. Incorporation of this mechanistic knowledge into the development of a live-attenuated ZIKV vaccine restricts its ST potential.

The worldwide seroprevalence of DENV, CHIKV and ZIKV infection: A systematic review and meta-analysis

BACKGROUND

As the three major arthropod-borne viruses, dengue virus (DENV), chikungunya virus (CHIKV), and zika virus (ZIKV) are posing a growing threat to global public health and socioeconomic development. Our study aimed to systematically review the global seroprevalences of these arboviruses from existing publications.

METHODS

Articles published between Jan 01, 2000 and Dec 31, 2019 in the databases of Embase, Pubmed and Web of Science were searched and collected. Countries or areas with known local presence of Aedes vector mosquitoes were included. Random effects model was utilized to estimate the pooled seroprevalences and the proportion of inapparent infection.

RESULTS

Out of 1375, a total of 133 articles involving 176,001 subjects were included for our analysis. The pooled seroprevalences of DENV, CHIKV and ZIKV were 38%, 25% and 18%, respectively; and their corresponding proportions of inapparent infections were 80%, 40% and 50%. The South-East Asia Region had the highest seroprevalences of DENV and CHIKV, while the Region of the Americas had the highest seroprevalence of ZIKV. The seroprevalences of DENV and CHIKV were similar when comparing developed and developing countries, urban and rural areas, or among different populations. In addition, we observed a decreased global seroprevalences in the new decade (2010-2019) comparing to the decade before (2000-2009) for CHIKV. For ZIKV, the positive rates tested with the nucleic acid detection method were lower than those tested with the antibody detection method. Lastly, numerous cases of dual seropositivity for CHIKV and DENV were reported.

CONCLUSIONS

Our results revealed a varied prevalence of arbovirus infections in different geographical regions and countries, and the inapparent infection accounted an unneglected portion of infections that requires more attention. This study will shed lights on our understanding of the true burden of arbovirus infections and promote appropriate vaccination in the future.

The dinucleotide composition of the Zika virus genome is shaped by conflicting evolutionary pressures in mammalian hosts and mosquito vectors

Most vertebrate RNA viruses show pervasive suppression of CpG and UpA dinucleotides, closely resembling the dinucleotide composition of host cell transcriptomes. In contrast, CpG suppression is absent in both invertebrate mRNA and RNA viruses that exclusively infect arthropods. Arthropod-borne (arbo) viruses are transmitted between vertebrate hosts by invertebrate vectors and thus encounter potentially conflicting evolutionary pressures in the different cytoplasmic environments. Using a newly developed Zika virus (ZIKV) model, we have investigated how demands for CpG suppression in vertebrate cells can be reconciled with potentially quite different compositional requirements in invertebrates and how this affects ZIKV replication and transmission. Mutant viruses with synonymously elevated CpG or UpA dinucleotide frequencies showed attenuated replication in vertebrate cell lines, which was rescued by knockout of the zinc-finger antiviral protein (ZAP). Conversely, in mosquito cells, ZIKV mutants with elevated CpG dinucleotide frequencies showed substantially enhanced replication compared to wild type. Host-driven effects on virus replication attenuation and enhancement were even more apparent in mouse and mosquito models. Infections with CpG- or UpA-high ZIKV mutants in mice did not cause typical ZIKV-induced tissue damage and completely protected mice during subsequent challenge with wild-type virus, which demonstrates their potential as live-attenuated vaccines. In contrast, the CpG-high mutants displayed enhanced replication in Aedes aegypti mosquitoes and a larger proportion of mosquitoes carried infectious virus in their saliva. These findings show that mosquito cells are also capable of discriminating RNA based on dinucleotide composition. However, the evolutionary pressure on the CpG dinucleotides of viral genomes in arthropod vectors directly opposes the pressure present in vertebrate host cells, which provides evidence that an adaptive compromise is required for arbovirus transmission. This suggests that the genome composition of arbo flaviviruses is crucial to maintain the balance between high-level replication in the vertebrate host and persistent replication in the mosquito vector.

The genome of the flavivirus Zika virus is stuck in a tug-of-war between two directly opposing evolutionary pressures that are present in the cells of mammalian host organisms and mosquito vectors; this results in an adaptive compromise, as manifested in the virus’s genome dinucleotide composition.

Knowledge of Zika Virus Transmission and Its Prevention among High-Risk Pregnant Women in Brazil

Recent outbreaks of Zika virus (ZIKV) infection highlight the urgent need to evaluate the efficacy of current public health measures to educate susceptible groups about how to prevent infection, modes of viral transmission, and consequences of infection. We performed a cross-sectional study in the city of Jundiaí, São-Paulo, from March 2016 to August 2017. In 315 high-risk pregnant women we evaluated the rate of ZIKV infection, knowledge of pathways of ZIKV transmission, and the use of protective measures. Data were analyzed and correlated with sociodemographic variables. The rate of ZIKV infection was 10.8%. ZIKV transmission by mosquitoes was the best-known means of virus acquisition, while transmission of ZIKV by sexual intercourse as well as mother–fetus transmission was known by less than half of the women. The use of insect repellent, reported by 53% of participants, was correlated with higher education and personal directives from health professionals. Condom use was reported by 19.5% of subjects. Improved strategies to increase awareness of ZIKV infection and its consequences, designed to appeal to specific, targeted populations, are clearly necessary to more accurately prevent the spread of this infection and diminish adverse consequences in the pregnant population.

Outcomes from international field trials with Male Aedes Sound Traps: Frequency-dependent effectiveness in capturing target species in relation to bycatch abundance

Aedes aegypti and Aedes albopictus vector dengue, chikungunya and Zika viruses. With both species expanding their global distributions at alarming rates, developing effective surveillance equipment is a continuing priority for public health researchers. Sound traps have been shown, in limited testing, to be highly species-specific when emitting a frequency corresponding to a female mosquito wingbeat. Determining male mosquito capture rates in sound traps based on lure frequencies in endemic settings is the next step for informed deployment of these surveillance tools. We field-evaluated Male Aedes Sound Traps (MASTs) set to either 450 Hz, 500 Hz, 550 Hz or 600 Hz for sampling Aedes aegypti and/or Aedes albopictus and compared catch rates to BG-Sentinel traps within Pacific (Madang, Papua New Guinea) and Latin American (Molas, Mexico and Orange Walk Town, Belize) locations. MASTs set to 450-550 Hz consistently caught male Ae. aegypti at rates comparable to BG-Sentinel traps in all locations. A peak in male Ae. albopictus captures in MASTs set at 550 Hz was observed, with the lowest mean abundance recorded in MASTs set to 450 Hz. While significantly higher abundances of male Culex were sampled in MASTs emitting lower relative frequencies in Molas, overall male Culex were captured in significantly lower abundances in the MASTs, relative to BG-Sentinel traps within all locations. Finally, significant differences in rates at which male Aedes and Culex were positively detected in trap-types per weekly collections were broadly consistent with trends in abundance data per trap-type. MASTs at 550 Hz effectively captured both male Ae. aegypti and Ae. albopictus while greatly reducing bycatch, especially male Culex, in locations where dengue transmission has occurred. This high species-specificity of the MAST not only reduces staff-time required to sort samples, but can also be exploited to develop an accurate smart-trap system-both outcomes potentially reducing public health program expenses.

Role of mutational reversions and fitness restoration in Zika virus spread to the Americas

Zika virus (ZIKV) emerged from obscurity in 2013 to spread from Asia to the South Pacific and the Americas, where millions of people were infected, accompanied by severe disease including microcephaly following congenital infections. Phylogenetic studies have shown that ZIKV evolved in Africa and later spread to Asia, and that the Asian lineage is responsible for the recent epidemics in the South Pacific and Americas. However, the reasons for the sudden emergence of ZIKV remain enigmatic. Here we report evolutionary analyses that revealed four mutations, which occurred just before ZIKV introduction to the Americas, represent direct reversions of previous mutations that accompanied earlier spread from Africa to Asia and early circulation there. Our experimental infections of Aedes aegypti mosquitoes, human cells, and mice using ZIKV strains with and without these mutations demonstrate that the original mutations reduced fitness for urban, human-amplifed transmission, while the reversions restored fitness, increasing epidemic risk. These findings include characterization of three transmission-adaptive ZIKV mutations, and demonstration that these and one identified previously restored fitness for epidemic transmission soon before introduction into the Americas. The initial mutations may have followed founder effects and/or drift when the virus was introduced decades ago into Asia.

Update on the Transmission of Zika Virus Through Breast Milk and Breastfeeding: A Systematic Review of the Evidence

We systematically searched regional and international databases and screened 1658 non-duplicate records describing women with suspected or confirmed ZIKV infection, intending to breastfeed or give breast milk to an infant to examine the potential of mother-to-child transmission of Zika virus (ZIKV) through breast milk or breastfeeding-related practices. Fourteen studies met our inclusion criteria and inform this analysis. These studies reported on 97 mother-children pairs who provided breast milk for ZIKV assessment. Seventeen breast milk samples from different women were found positive for ZIKV via RT-PCR, and ZIKV replication was found in cell cultures from five out of seven breast milk samples from different women. Only three out of six infants who had ZIKV infection were breastfed, no evidence of clinical complications was found to be associated with ZIKV RNA in breast milk. This review updates our previous report by including 12 new articles, in which we found no evidence of ZIKV mother-to-child transmission through breast milk intake or breastfeeding. As the certainty of the present evidence is low, additional studies are still warranted to determine if ZIKV can be transmitted through breastfeeding.

A Review of the Control of Aedes aegypti (Diptera: Culicidae) in the Continental United States

Aedes aegypti (L) is an anthropophilic mosquito involved in the transmission of a variety of viral pathogens worldwide including dengue, chikungunya, yellow fever, and Zika viruses. This species, native to Africa, is well established in the continental U.S. (CONUS) and occasionally contributes to localized outbreaks of viral diseases. In the last seven decades, mosquito control programs in the CONUS have been focused on vectors of eastern equine encephalitis, St. Louis encephalitis, and West Nile viruses, as well as nuisance species. Aedes aegypti receives little control focus except during outbreak periods, which has led to a lack of information on appropriate and effective control options targeting Ae. aegypti in the CONUS. As such, in the event of an Ae. aegypti-borne arboviral outbreak in the CONUS, there are limited evidence-based control recommendations or protocols in place. Autochthonous outbreaks of Ae. aegypti-borne pathogens have occurred recently in the CONUS, including dengue outbreaks in 2010 and 2013, a chikungunya outbreak in 2014, and the 2016 outbreak of Zika virus. The increasing frequency of Ae. aegypti-borne outbreaks necessitates increased attention and research on control of this species to prevent and mitigate future outbreaks. This review consolidates and synthesizes the available literature on control of Ae. aegypti, specifically within the CONUS, focusing on data generated through operational applications as well as field and semifield experiments. The purpose of this review is to identify and highlight areas where additional research is needed. The review covers chemical control and insecticide resistance, biological control, source reduction, trapping, and alternative techniques.

Asynchronicity of endemic and emerging mosquito-borne disease outbreaks in the Dominican Republic

Mosquito-borne viruses threaten the Caribbean due to the region's tropical climate and seasonal reception of international tourists. Outbreaks of chikungunya and Zika have demonstrated the rapidity with which these viruses can spread. Concurrently, dengue fever cases have climbed over the past decade. Sustainable disease control measures are urgently needed to quell virus transmission and prevent future outbreaks. Here, to improve upon current control methods, we analyze temporal and spatial patterns of chikungunya, Zika, and dengue outbreaks reported in the Dominican Republic between 2012 and 2018. The viruses that cause these outbreaks are transmitted by Aedes mosquitoes, which are sensitive to seasonal climatological variability. We evaluate whether climate and the spatio-temporal dynamics of dengue outbreaks could explain patterns of emerging disease outbreaks. We find that emerging disease outbreaks were robust to the climatological and spatio-temporal constraints defining seasonal dengue outbreak dynamics, indicating that constant surveillance is required to prevent future health crises.

EVs Containing Host Restriction Factor IFITM3 Inhibited ZIKV Infection of Fetuses in Pregnant Mice through Trans-placenta Delivery

Zika virus (ZIKV) infection can lead to neurological complications and fetal defects, and it has attracted global public health concerns. Effective treatment for ZIKV infection remains elusive, and a preventative vaccine is not yet available. Therapeutics for fetuses need to overcome placenta barriers to reach the fetuses and require higher safety standards. In the present study, we engineered mammalian extracellular vesicles (EVs) to deliver a host restriction factor, interferon-induced transmembrane protein 3 (IFITM3), for the treatment of ZIKV infection. Our results demonstrated that the IFITM3-containing EVs (IFITM3-Exos) suppressed ZIKV viremia by a 2-log reduction in pregnant mice. Moreover, the engineered EVs effectively delivered IFITM3 protein across the placental barrier and suppressed ZIKV in the fetuses with significant reduction of viremia in key fetal organs as measured by quantitative real-time PCR. Mechanistic study showed that IFITM3 was delivered to late endosomes/lysosomes where it inhibited viral entry into the host cells. Our study demonstrated that EVs could act as a cross-placenta drug delivery vehicle to the fetus, and IFITM3, an endogenous restriction factor, is a potential treatment for ZIKV infection during pregnancy.

Spatiotemporal Distribution of Zika Virus and Its Spatially Heterogeneous Relationship with the Environment

Infectious diseases have caused some of the most feared plagues and greatly harmed human health. However, despite the qualitative understanding that the occurrence and diffusion of infectious disease is related to the environment, the quantitative relations are unknown for many diseases. Zika virus (ZIKV) is a mosquito-borne virus that poses a fatal threat and has spread explosively throughout the world, impacting human health. From a geographical perspective, this study aims to understand the global hotspots of ZIKV as well as the spatially heterogeneous relationship between ZIKV and environmental factors using exploratory special data analysis (ESDA) model. A geographically weighted regression (GWR) model was used to analyze the influence of the dominant environmental factors on the spread of ZIKV at the continental scale. The results indicated that ZIKV transmission had obvious regional and seasonal heterogeneity. Population density, GDP per capita, and landscape fragmentation were the dominant environmental factors affecting the spread of ZIKV, which indicates that social factors had a greater influence than natural factors on the spread of it. As SARS-CoV-2 is spreading globally, this study can provide methodological reference for fighting against the pandemic.

Detection of dengue, chikungunya, and Zika RNA in blood donors from Southeast Asia

BACKGROUND

Chikungunya (CHIKV), dengue (DENV), and Zika (ZIKV) viruses are of concern due to the potential of transfusion transmission in blood, especially in regions such as Southeast Asia where the viruses are endemic. The recent availability of nucleic acid testing (NAT) to screen blood donations on an automated platform provides the opportunity to detect potentially infectious units in asymptomatic donors.

STUDY DESIGN AND METHODS

Three thousand blood donations from Vietnam and 6000 from Thailand were screened with a real-time polymerase chain reaction (PCR) test (cobas CHIKV/DENV, Roche Diagnostics, Indianapolis, IN) and equal numbers on cobas Zika (Roche Diagnostics). Reactive samples were tested by alternative NAT with resolution of discordant results by heminested PCR. Throughput of simultaneous testing of the two assays on the cobas 8800 system (Roche Diagnostics) was evaluated.

RESULTS

In Vietnam, 9 of 3045 samples were reactive for DENV and all were confirmed, for a prevalence (with 95% confidence interval [CI]) of 0.296% (0.135-0.560). In Thailand, 2 of 6000 samples were reactive for CHIKV, 4 of 6000 for DENV, and 1 of 6005 for ZIKV, and all confirmed. The prevalence of CHIKV is 0.033% (0.004-0.120), DENV 0.067% (0.018-0.171), and ZIKV 0.017% (0.000-0.093). The overall specificity for the cobas CHIKV/DENV and cobas Zika tests was 100% (99.959-100). For the simultaneous assay testing, 960 test results were available in 7 hours and 53 minutes.

CONCLUSION

Detection of CHIKV, DENV, and ZIKV RNA in donor samples in Vietnam and Thailand indicate the presence of the virus in asymptomatic blood donors. The cobas 6800/8800 systems (Roche Molecular Systems, Pleasanton, CA) enable screening blood donations in endemic areas for these viruses together or separately.

Congenital Zika syndrome: A systematic review

BACKGROUND

The signs and symptoms of Zika virus infection are usually mild and self-limited. However, the disease has been linked to neurological complications such as Guillain-Barré syndrome and peripheral nerve involvement, and also to abortion and fetal deaths due to vertical transmission, resulting in various congenital malformations in newborns, including microcephaly. This review aimed to describe the o signs and symptoms that characterize the congenital Zika syndrome.

METHODS AND FINDINGS

A systematic review was performed with a protocol and described according to the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The search strategy yielded 2,048 studies. After the exclusion of duplicates and application of inclusion criteria, 46 studies were included. The main signs and symptoms associated with the congenital Zika syndrome were microcephaly, parenchymal or cerebellar calcifications, ventriculomegaly, central nervous system hypoplasia or atrophy, arthrogryposis, ocular findings in the posterior and anterior segments, abnormal visual function and low birthweight for gestational age.

CONCLUSIONS

Zika virus infection during pregnancy can cause a series of changes in the growth and development of children, while impacting the healthcare system due to the severity of cases. Our findings outline the disease profile in newborns and infants and may contribute to the development and updating of more specific clinical protocols.

Modeling intra-mosquito dynamics of Zika virus and its dose-dependence confirms the low epidemic potential of Aedes albopictus

Originating from African forests, Zika virus (ZIKV) has now emerged worldwide in urbanized areas, mainly transmitted by Aedes aegypti mosquitoes. Although Aedes albopictus can transmit ZIKV experimentally and was suspected to be a ZIKV vector in Central Africa, the potential of this species to sustain virus transmission was yet to be uncovered until the end of 2019, when several autochthonous transmissions of the virus vectored by Ae. albopictus occurred in France. Aside from these few locally acquired ZIKV infections, most territories colonized by Ae. albopictus have been spared so far. The risk level of ZIKV emergence in these areas remains however an open question. To assess Ae. albopictus' vector potential for ZIKV and identify key virus outbreak predictors, we built a complete framework using the complementary combination of (i) dose-dependent experimental Ae. albopictus exposure to ZIKV followed by time-dependent assessment of infection and systemic infection rates, (ii) modeling of intra-human ZIKV viremia dynamics, and (iii) in silico epidemiological simulations using an Agent-Based Model. The highest risk of transmission occurred during the pre-symptomatic stage of the disease, at the peak of viremia. At this dose, mosquito infection probability was estimated to be 20%, and 21 days were required to reach the median systemic infection rates. Mosquito population origin, either temperate or tropical, had no impact on infection rates or intra-host virus dynamic. Despite these unfavorable characteristics for transmission, Ae. albopictus was still able to trigger and yield large outbreaks in a simulated environment in the presence of sufficiently high mosquito biting rates. Our results reveal a low but existing epidemic potential of Ae. albopictus for ZIKV, that might explain the absence of large scale ZIKV epidemics so far in territories occupied only by Ae. albopictus. They nevertheless support active surveillance and eradication programs in these territories to maintain the risk of emergence to a low level.

CRISPR/Cas9 knockout of female-biased genes AeAct-4 or myo-fem in Ae. aegypti results in a flightless phenotype in female, but not male mosquitoes

Aedes aegypti is a vector of dengue, chikungunya, and Zika viruses. Current vector control strategies such as community engagement, source reduction, and insecticides have not been sufficient to prevent viral outbreaks. Thus, interest in novel strategies involving genetic engineering is growing. Female mosquitoes rely on flight to mate with males and obtain a bloodmeal from a host. We hypothesized that knockout of genes specifically expressed in female mosquitoes associated with the indirect flight muscles would result in a flightless female mosquito. Using CRISPR-Cas9 we generated loss-of-function mutations in several genes hypothesized to control flight in mosquitoes, including actin (AeAct-4) and myosin (myo-fem) genes expressed specifically in the female flight muscle. Genetic knockout of these genes resulted in 100% flightless females, with homozygous males able to fly, mate, and produce offspring, albeit at a reduced rate when compared to wild type males. Interestingly, we found that while AeAct-4 was haplosufficient, with most heterozygous individuals capable of flight, this was not the case for myo-fem, where about half of individuals carrying only one intact copy could not fly. These findings lay the groundwork for developing novel mechanisms of controlling Ae. aegypti populations, and our results suggest that this mechanism could be applicable to other vector species of mosquito.

Communicating the risk of contracting Zika virus to low income underserved pregnant Latinas: A clinic-based study

OBJECTIVE

Frequent travel between the Southern border states in the USA, Mexico, and Latin American countries increases the risk of the Zika virus (ZIKV) spread. Patient education on virus transmission is fundamental in decreasing the number of imported cases, particularly among pregnant women.

METHODS

The study used cross-sectional methodology to investigate information sources and knowledge concerning the ZIKV virus among 300 under-served pregnant Latinas recruited from prenatal care clinics in the North Texas region. Bivariate and multiple logistic regression models were used to investigate associations between the primary outcomes and patient characteristics.

RESULTS

Physicians, nurses, and families are the major sources for pregnancy information, while media/internet (65%) and physician/nurse (33%) are the main sources for ZIKV information. Less than one-half of the mothers reported that their physician/nurse did not discuss safe sexual practices or inquired about their sexual practices. A considerable proportion of women from the community clinic were neither warned nor queried about travel to ZIKV risk countries. There is an overall understanding of Zika virus transmission, symptoms, complications, and recommended guidelines. Younger age and single mother status are risk factors for lack of ZIKV knowledge. Foreign-born mothers are 2.5-3.0 times more likely to have knowledge on disease transmission, symptoms, and microcephaly condition. While, younger mothers (18-24) are less likely to have knowledge of ZIKV infection symptoms (fever, rash and pink eye) and transmission of infection via unprotected sexual (vaginal, anal, or oral) behavior, compared to older mothers.

CONCLUSIONS

Interventions are needed to heighten the knowledge of ZIKV, particularly among women of reproductive age and their male partners in the community health care setting. Our study underscores the need for health care providers to be trained in delivering messages to enhance risk perception during health emergencies to vulnerable and underserved families (lower economic background, language ability, and culture). During health emergencies, clinics must disseminate crucial information via multi modalities to ensure messages reach the targeted patients.

The effects of exposure to pyriproxyfen and predation on Zika virus infection and transmission in Aedes aegypti

Zika virus (ZIKV) is an emerging mosquito-borne pathogen that can cause global public health threats. In the absence of effective antiviral medications, prevention measures rely largely on reducing the number of adult mosquito vectors by targeting juvenile stages. Despite the importance of juvenile mosquito control measures in reducing adult population size, a full understanding of the effects of these measures in determining mosquito phenotypic traits and in mosquito-arbovirus interactions is poorly understood. Pyriproxyfen is a juvenile hormone analog that primarily blocks adult emergence, but does not cause mortality in larvae. This mechanism has the potential to work in combination with other juvenile sources of mortality in nature such as predation to affect mosquito populations. Here, we experimentally evaluated the effects of juvenile exposure to pyriproxyfen and predatory mosquito Toxorhynchites rutilus on Aedes aegypti phenotypes including susceptibility to ZIKV infection and transmission. We discovered that combined effects of pyriproxyfen and Tx. rutilus led to higher inhibition of adult emergence in Ae. aegypti than observed in pyriproxyfen or Tx. rutilus treatments alone. Adult body size was larger in treatments containing Tx. rutilus and in treatments mimicking the daily mortality of predation compared to control or pyriproxyfen treatments. Susceptibility to infection with ZIKV in Ae. aegypti was reduced in predator treatment relative to those exposed to pyriproxyfen. Disseminated infection, transmission, and titers of ZIKV in Ae. aegypti were similar in all treatments relative to controls. Our data suggest that the combination of pyriproxyfen and Tx. rutilus can inhibit adult Ae. aegypti emergence but may confer a fitness advantage in survivors and does not inhibit their vector competence for ZIKV relative to controls. Understanding the ultimate consequences of juvenile mosquito control measures on subsequent adults’ ability to transmit pathogens is critical to fully understand their overall impacts.

Mosquito control approaches primarily depend on lowering the number of potential adult mosquito vectors by inhibiting juvenile stages to reduce the risk of pathogen transmission. Pyriproxyfen is a juvenile hormone analog that inhibits the emergence of adult mosquitoes by interrupting metamorphosis, but does not target larvae. This mechanism allows natural sources of mortality like predation to act in combination with pyriproxyfen to affect mosquito population size. Here, we determined the effects of juvenile exposure to pyriproxyfen and predatory mosquito Toxorhynchites rutilus on adult Aedes aegypti traits, including infection with Zika virus. Combined effects of pyriproxyfen and Tx. rutilus led to strong inhibition of adult emergence in Ae. aegypti. Treatments containing predators or those mimicking the daily mortality of predation produced larger sized adults. Susceptibility to ZIKV infection was lowest in the predator treatment and highest in the pyriproxyfen treatment. Disseminated infection, transmission, and viral titers of ZIKV were similar between treatments. Our data suggest that the combination of pyriproxyfen and predators can enhance inhibition of adult Ae. aegypti emergence, but survivors may have fitness benefits such being larger mosquitoes. Understanding the consequences of control approaches in mosquito-pathogen interactions will assist to evaluate their suitability in mosquito control programs.

HSV-1 and Zika Virus but Not SARS-CoV-2 Replicate in the Human Cornea and Are Restricted by Corneal Type III Interferon

Here, we report our studies of immune-mediated regulation of Zika virus (ZIKV), herpes simplex virus 1 (HSV-1), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in the human cornea. We find that ZIKV can be transmitted via corneal transplantation in mice. However, in human corneal explants, we report that ZIKV does not replicate efficiently and that SARS-CoV-2 does not replicate at all. Additionally, we demonstrate that type III interferon (IFN-λ) and its receptor (IFNλR1) are expressed in the corneal epithelium. Treatment of human corneal explants with IFN-λ, and treatment of mice with IFN-λ eye drops, upregulates antiviral interferon-stimulated genes. In human corneal explants, blockade of IFNλR1 enhances replication of ZIKV and HSV-1 but not SARS-CoV-2. In addition to an antiviral role for IFNλR1 in the cornea, our results suggest that the human cornea does not support SARS-CoV-2 infection despite expression of ACE2, a SARS-CoV-2 receptor, in the human corneal epithelium.

No evidence for sylvatic cycles of chikungunya, dengue and Zika viruses in African green monkeys (Chlorocebus aethiops sabaeus) on St. Kitts, West Indies

BACKGROUND

Dengue, chikungunya and Zika viruses (DENV, CHIKV and ZIKV) are transmitted in sylvatic transmission cycles between non-human primates and forest (sylvan) mosquitoes in Africa and Asia. It remains unclear if sylvatic cycles exist or could establish themselves elsewhere and contribute to the epidemiology of these diseases. The Caribbean island of St. Kitts has a large African green monkey (AGM) (Chlorocebus aethiops sabaeus) population and is therefore ideally suited to investigate sylvatic cycles.

METHODS

We tested 858 AGM sera by ELISA and PRNT for virus-specific antibodies and collected and identified 9704 potential arbovirus vector mosquitoes. Mosquitoes were homogenized in 513 pools for testing by viral isolation in cell culture and by multiplex RT-qPCR after RNA extraction to detect the presence of DENV, CHIKV and ZIKVs. DNA was extracted from 122 visibly blood-fed individual mosquitoes and a polymorphic region of the hydroxymethylbilane synthase gene (HMBS) was amplified by PCR to determine if mosquitoes had fed on AGMs or humans.

RESULTS

All of the AGMs were negative for DENV, CHIKV or ZIKV antibodies. However, one AGM did have evidence of an undifferentiated Flavivirus infection. Similarly, DENV, CHIKV and ZIKV were not detected in any of the mosquito pools by PCR or culture. AGMs were not the source of any of the mosquito blood meals.

CONCLUSION

Sylvatic cycles involving AGMs and DENV, CHIKV and ZIKV do not currently exist on St. Kitts.

The recently introduced Aedes albopictus in Tunisia has the potential to transmit chikungunya, dengue and Zika viruses

The mosquito Aedes albopictus was detected for the first time in Tunisia in 2018. With its establishment in the capital city of Tunis, local health authorities fear the introduction of new human arboviral diseases, like what happened in Europe with unexpected local cases of chikungunya, dengue and Zika. Even though this mosquito is competent to transmit the arboviruses mentioned above, the transmission level will vary depending on the couple, mosquito population and virus genotype. Here, we assessed the vector competence of Ae. albopictus Tunisia by experimental infections with chikungunya (CHIKV), dengue (DENV), and Zika (ZIKV) viruses. We found that Ae. albopictus Tunisia was highly competent for CHIKV (transmission efficiency of 25% at 21 post-infection) and to a lesser extent, for ZIKV (8.7%) and DENV (8.3%). Virus was detected in mosquito saliva at day 3 (CHIKV), day 10 (ZIKV) and day 21 (DENV) post-infection. These results suggest that the risk of emergence of chikungunya is the highest imposing a more sustained surveillance to limit Ae. albopictus populations in densely populated urban dwellings and at the entry points of travelers returning from CHIKV-endemic regions.

Spatiotemporal transmission dynamics of co-circulating dengue, Zika, and chikungunya viruses in Fortaleza, Brazil: 2011-2017

The mosquito-borne viruses dengue (DENV), Zika (ZIKV), and chikungunya (CHIKV), now co-endemic in the Americas, pose growing threats to health worldwide. However, it remains unclear whether there exist interactions between these viruses that could shape their epidemiology. This study advances knowledge by assessing the transmission dynamics of co-circulating DENV, ZIKV, and CHIKV in the city of Fortaleza, Brazil. Spatiotemporal transmission dynamics of DENV, ZIKV, and CHIKV were analyzed using georeferenced data on over 210,000 reported cases from 2011 to 2017 in Fortaleza, Brazil. Local spatial clustering tests and space-time scan statistics were used to compare transmission dynamics across all years. The transmission of co-circulating viruses in 2016 and 2017 was evaluated at fine spatial and temporal scales using a measure of spatiotemporal dependence, the τ-statistic. Results revealed differences in the diffusion of CHIKV compared to previous DENV epidemics and spatially distinct transmission of DENV/ZIKV and CHIKV during the period of their co-circulation. Significant spatial clustering of viruses of the same type was observed within 14-day time intervals at distances of up to 6.8 km (p<0.05). These results suggest that arbovirus risk is not uniformly distributed within cities during co-circulation. Findings may guide outbreak preparedness and response efforts by highlighting the clustered nature of transmission of co-circulating arboviruses at the neighborhood level. The potential for competitive interactions between the arboviruses should be further investigated.

Reversion to ancestral Zika virus NS1 residues increases competence of Aedes albopictus

Both mosquito species-specific differences and virus strain -specific differences impact vector competence. Previous results in our laboratory with individual populations of N. American mosquitoes support studies suggesting Aedes aegypti are more competent than Ae. albopictus for American Zika virus (ZIKV) strains and demonstrate that U.S. Ae. albopictus have higher competence for an ancestral Asian ZIKV strain. A982V, an amino acid substitution in the NS1 gene acquired prior to the American outbreak, has been shown to increase competence in Ae. aegypti. We hypothesized that variability in the NS1 could therefore contribute to species-specific differences and developed a reverse genetics system based on a 2016 ZIKV isolate from Honduras (ZIKV-WTic) to evaluate the phenotypic correlates of individual amino acid substitutions. In addition to A982V, we evaluated G894A, which was acquired during circulation in the Americas. Reversion of 982 and 894 to ancestral residues increased infectivity, transmissibility and viral loads in Ae. albopictus but had no effect on competence or replication in Ae. aegypti. In addition, while host cell-specific differences in NS1 secretion were measured, with significantly higher secretion in mammalian cells relative to mosquito cells, strain-specific differences in secretion were not detected, despite previous reports. These results demonstrate that individual mutations in NS1 can influence competence in a species-specific manner independent of differences in NS1 secretion and further indicate that ancestral NS1 residues confer increased competence in Ae. albopictus. Lastly, experimental infections of Ifnar1-/- mice demonstrated that these NS1 substitutions can influence viral replication in the host and, specifically, that G894A could represent a compensatory change following a fitness loss from A982V with some viral genetic backgrounds. Together these data suggest a possible role for epistatic interactions in ZIKV fitness in invertebrate and vertebrate hosts and demonstrate that strains with increased transmission potential in U.S. Ae. albopictus could emerge.

Surveillance of Aedes aegypti populations in the city of Praia, Cape Verde: Zika virus infection, insecticide resistance and genetic diversity

BACKGROUND

Aedes spp. are responsible for the transmission of many arboviruses, which contribute to rising human morbidity and mortality worldwide. The Aedes aegypti mosquito is a main vector for chikungunya, dengue and yellow fever infections, whose incidence have been increasing and distribution expanding. This vector has also driven the emergence of the Zika virus (ZIKV), first reported in Africa which spread rapidly to Asia and more recently across the Americas. During the outbreak in the Americas, Cape Verde became the first African country declaring a Zika epidemic, with confirmed cases of microcephaly. Here we investigate the prevalence of ZIKV and dengue (DENV) infected Ae. aegypti mosquitoes in the weeks following the outbreak in Cape Verde, and the presence of insecticide resistance in the circulating vector population. Genetic diversity in the mosquito population was also analysed.

METHODS

From August to October 2016, 816 Ae. aegypti mosquitoes were collected in several locations across Praia, Cape Verde, the major hot spot of reported ZIKV cases in the country. All mosquitoes were screened by reverse transcription PCR for ZIKV and DENV, and a subset (n = 220) were screened for knockdown insecticide resistance associated mutations in the voltage gated sodium channel (VGSC) gene by capillary sequencing. The mitochondrial NADH dehydrogenase subunit 4 (nad4) gene was sequenced in 100 mosquitoes. These data were compared to 977 global sequences in a haplotype network and a phylogenetic tree analysis.

RESULTS

Two Ae. aegypti mosquitoes were ZIKV positive (0.25%). There were no SNP mutations found in the VGSC gene associated with insecticide resistance. Analysis of the nad4 gene revealed 11 haplotypes in the Cape Verdean samples, with 5 being singletons. Seven haplotypes were exclusive to Cape Verde. Several of the remaining haplotypes were frequent in the global dataset, being present in several countries (including Cape Verde) across five different continents. The most common haplotype in Cape Verde (50.6 %) was also found in Africa and South America.

CONCLUSIONS

There was low-level Zika virus circulation in mosquitoes from Praia shortly after the outbreak. The Ae. aegypti population did not appear to have the kdr mutations associated with pyrethroid resistance. Furthermore, haplotype and phylogenetic analyses revealed that Cape Verde Ae. aegypti mosquitoes are most closely related to those from other countries in Africa and South America.