West Nile virus and its vectors

Impact of climate change on the global circulation of West Nile virus and adaptation responses: a scoping review

BACKGROUND

West Nile virus (WNV), the most widely distributed flavivirus causing encephalitis globally, is a vector-borne pathogen of global importance. The changing climate is poised to reshape the landscape of various infectious diseases, particularly vector-borne ones like WNV. Understanding the anticipated geographical and range shifts in disease transmission due to climate change, alongside effective adaptation strategies, is critical for mitigating future public health impacts. This scoping review aims to consolidate evidence on the impact of climate change on WNV and to identify a spectrum of applicable adaptation strategies.

MAIN BODY

We systematically analyzed research articles from PubMed, Web of Science, Scopus, and EBSCOhost. Our criteria included English-language research articles published between 2007 and 2023, focusing on the impacts of climate change on WNV and related adaptation strategies. We extracted data concerning study objectives, populations, geographical focus, and specific findings. Literature was categorized into two primary themes: 1) climate-WNV associations, and 2) climate change impacts on WNV transmission, providing a clear understanding. Out of 2168 articles reviewed, 120 met our criteria. Most evidence originated from North America (59.2%) and Europe (28.3%), with a primary focus on human cases (31.7%). Studies on climate-WNV correlations (n = 83) highlighted temperature (67.5%) as a pivotal climate factor. In the analysis of climate change impacts on WNV (n = 37), most evidence suggested that climate change may affect the transmission and distribution of WNV, with the extent of the impact depending on local and regional conditions. Although few studies directly addressed the implementation of adaptation strategies for climate-induced disease transmission, the proposed strategies (n = 49) fell into six categories: 1) surveillance and monitoring (38.8%), 2) predictive modeling (18.4%), 3) cross-disciplinary collaboration (16.3%), 4) environmental management (12.2%), 5) public education (8.2%), and 6) health system readiness (6.1%). Additionally, we developed an accessible online platform to summarize the evidence on climate change impacts on WNV transmission ( https://2xzl2o-neaop.shinyapps.io/WNVScopingReview/ ).

CONCLUSIONS

This review reveals that climate change may affect the transmission and distribution of WNV, but the literature reflects only a small share of the global WNV dynamics. There is an urgent need for adaptive responses to anticipate and respond to the climate-driven spread of WNV. Nevertheless, studies focusing on these adaptation responses are sparse compared to those examining the impacts of climate change. Further research on the impacts of climate change and adaptation strategies for vector-borne diseases, along with more comprehensive evidence synthesis, is needed to inform effective policy responses tailored to local contexts.

Seroprevalence of West Nile Virus among Equids in Bulgaria in 2022 and Assessment of Some Risk Factors

The aim of this study was to analyze the seroprevalence of West Nile virus (WNV) among equids in Bulgaria, confirm the results of a competitive ELISA versus the virus neutralization test (VNT) and investigate some predisposing factors for WNV seropositivity. A total of 378 serum samples from 15 provinces in northern and southern Bulgaria were tested. The samples originated from 314 horses and 64 donkeys, 135 males and 243 females, aged from 1 to 30 years. IgG and IgM antibodies against WNV protein E were detected by ELISA. ELISA-positive samples were additionally tested via VNT for WNV and Usutu virus. Thirty-five samples were WNV-positive by ELISA (9.26% [CI = 6.45-12.88]), of which 15 were confirmed by VNT; hence, the seroprevalence was 3.97% (CI = 2.22-6.55). No virus-neutralizing antibodies to Usutu virus were detected among the 35 WNV-ELISA-positive equids in Bulgaria. When compared with VNT, ELISA showed 100.0% sensitivity and 94.5% specificity. A statistical analysis showed that the risk factors associated with WNV seropositivity were the region (p < 0.0001), altitude of the locality (p < 0.0001), type of housing (p < 0.0001) and breed (p = 0.0365). The results of the study demonstrate, albeit indirectly, that WNV circulates among equids in northern and southern Bulgaria, indicating that they could be suitable sentinel animals for predicting human cases and determining the risk in these areas or regions of the country.

Whole-Blood PCR Preferred for Timely Diagnosis of Neuroinvasive West Nile Virus Infections: Lessons From the 2021 Arizona Outbreak

Background

In 2021, the state of Arizona experienced the largest focal outbreak of West Nile virus (WNV) in US history. Timely and accurate diagnostic testing remains a challenge for WNV due to transient viremia and limited immunoassay specificity. Recent studies have identified whole blood (WB) and urine as more sensitive specimen types for the detection of WNV RNA.

Methods

We evaluated ordering practices, test performance, and patient characteristics of probable and confirmed cases. In total, we identified 190 probable and proven cases, including 127 patients (66.8%) with neuroinvasive disease.

Results

Among all cases, only 29.5% had WNV polymerase chain reaction (PCR) testing ordered on WB, of which 80.3% resulted as positive, including 7 cases in which WNV serologic testing was negative and 5 cases for which serologic testing was not ordered. In comparison, only 23.7% of cases that had cerebrospinal fluid (CSF) PCR ordered had a positive result, including 3 cases that were negative by PCR on WB. In contrast, WNV PCR on WB detected 12 neuroinvasive cases that were CSF PCR negative. WNV PCR testing in urine was only ordered on 2 patients, both of whom were positive. Crossing cycle threshold (Ct) values were not significantly different between WB and CSF specimen types, nor was there a correlation between Ct value and days from symptom onset at the time of sample collection; all specimen types and time points had Ct values, with 98% above 30. WB was positive by WNV PCR in several patients for >7 days (range, 7-25 days) after symptom onset, as was the CSF PCR.

Conclusions

Taken together, these findings indicate that WNV PCR testing on WB may be the best initial test for timely diagnosis of WNV infection, irrespective of clinical manifestation; however, if negative in patients with suspected neuroinvasive disease, WNV PCR testing on CSF should be ordered.

Engagement of AKT and ERK signaling pathways facilitates infection of human neuronal cells with West Nile virus

West Nile virus (WNV) is an important neurotropic virus that accounts for the emergence of human arboviral encephalitis and meningitis. The interaction of WNV with signaling pathways plays a key role in controlling WNV infection. We have investigated the roles of the AKT and ERK pathways in supporting WNV propagation and modulating the inflammatory response following WNV infection. WNV established a productive infection in neuronal cell lines originated from human and mouse. Expression of IL-11 and TNF-α was markedly up-regulated in the infected human neuronal cells, indicating elicitation of inflammation response upon WNV infection. WNV incubation rapidly activated signaling cascades of AKT (AKT-S6-4E-BP1) and ERK (MEK-ERK-p90RSK) pathways. Treatment with AKT inhibitor MK-2206 or MEK inhibitor U0126 abrogated WNV-induced AKT or ERK activation. Strong activation of AKT and ERK signaling pathways could be detectable at 24 h after WNV infection, while such activation was abolished at 48 h post infection. U0126 treatment or knockdown of ERK expression significantly increased WNV RNA levels and viral titers and efficiently decreased IL-11 production induced by WNV, suggesting the involvement of ERK pathway in WNV propagation and IL-11 induction. MK-2206 treatment enhanced WNV RNA replication accompanied with a moderate decrease in IL-11 production. These results demonstrate that engagement of AKT and ERK signaling pathways facilitates viral infection and may be implicated in WNV pathogenesis.

Advances in research on arboviral acquisition from hosts to mosquitoes

Arboviral acquisition is a critical step in virus transmission. In this review, we present an overview of the interactions between viruses and host blood-derived factors, highlighting the diverse ways in which they interact. Moreover, the review outlines the impact of host blood on gut barriers during viral acquisition, emphasizing the crucial role of this physiological process in virus dissemination. Additionally, the review investigates the responses of symbioses to invading arboviruses, providing insights into the dynamic reactions of these vital relationships to the presence of arboviruses.

Ecological and clinical evidence of the establishment of West Nile virus in a large urban area in Europe, Berlin, Germany, 2021 to 2022

BackgroundWest Nile virus (WNV), found in Berlin in birds since 2018 and humans since 2019, is a mosquito-borne virus that can manifest in humans as West Nile fever (WNF) or neuroinvasive disease (WNND). However, human WNV infections and associated disease are likely underdiagnosed.AimWe aimed to identify and genetically characterise WNV infections in humans and mosquitoes in Berlin.MethodsWe investigated acute WNV infection cases reported to the State Office for Health and Social Affairs Berlin in 2021 and analysed cerebrospinal fluid (CSF) samples from patients with encephalitis of unknown aetiology (n = 489) for the presence of WNV. Mosquitoes were trapped at identified potential exposure sites of cases and examined for WNV infection.ResultsWest Nile virus was isolated and sequenced from a blood donor with WNF, a symptomatic patient with WNND and a WNND case retrospectively identified from testing CSF. All cases occurred in 2021 and had no history of travel 14 days prior to symptom onset (incubation period of the disease). We detected WNV in Culex pipiens mosquitoes sampled at the exposure site of one case in 2021, and in 2022. Genome analyses revealed a monophyletic Berlin-specific virus clade in which two enzootic mosquito-associated variants can be delineated based on tree topology and presence of single nucleotide variants. Both variants have highly identical counterparts in human cases indicating local acquisition of infection.ConclusionOur study provides evidence that autochthonous WNV lineage 2 infections occurred in Berlin and the virus has established an endemic maintenance cycle.

The Ongoing Epidemic of West Nile Virus in Greece: The Contribution of Biological Vectors and Reservoirs and the Importance of Climate and Socioeconomic Factors Revisited

Emerging infectious diseases have inflicted a significant health and socioeconomic burden upon the global population and governments worldwide. West Nile virus, a zoonotic, mosquito-borne flavivirus, was originally isolated in 1937 from a febrile patient in the West Nile Province of Uganda. It remained confined mainly to Africa, the Middle East, and parts of Europe and Australia until 1999, circulating in an enzootic mosquito-bird transmission cycle. Since the beginning of the 21st century, a new, neurotropic, more virulent strain was isolated from human outbreaks initially occurring in North America and later expanding to South and South-eastern Europe. Since 2010, when the first epidemic was recorded in Greece, annual incidence has fluctuated significantly. A variety of environmental, biological and socioeconomic factors have been globally addressed as potential regulators of the anticipated intensity of the annual incidence rate; circulation within the zoonotic reservoirs, recruitment and adaptation of new potent arthropod vectors, average winter and summer temperatures, precipitation during the early summer months, and socioeconomic factors, such as the emergence and progression of urbanization and the development of densely populated areas in association with insufficient health policy measures. This paper presents a review of the biological and socioenvironmental factors influencing the dynamics of the epidemics of West Nile virus (WNV) cases in Greece, one of the highest-ranked European countries in terms of annual incidence. To date, WNV remains an unpredictable opponent as is also the case with other emerging infectious diseases, forcing the National Health systems to develop response strategies, control the number of infections, and shorten the duration of the epidemics, thus minimizing the impact on human and material resources.

Monitoring the epidemic of West Nile virus in equids in Spain, 2020-2021

The largest epidemic of West Nile virus (WNV) reported ever in Spain in both humans and equines occurred in 2020, affecting 77 humans and 139 equine herds. Here, we aimed to monitor the outbreaks detected in equid herds in Andalusia (southern Spain), the Spanish region where 89.9% of the outbreaks were reported, and to evaluate the virus circulation and risk factor associated with WNV exposure in the affected herds. The first WNV case was detected in mid-July 2020, the number of outbreaks peaked in mid-August and the last one was confirmed on 26th October 2020. WNV lineage 1 was detected in 12 clinically affected horses using real time RT-PCR. Molecular analysis evidenced high nucleotide identity with WNV sequences obtained from humans, birds and mosquitoes from Spain and Italy between 2020 and 2022. Between five and eight months after the WNV epidemic, a total of 724 equids (including 485 unvaccinated and 239 vaccinated animals) from 113 of the 125 affected herds in Andalusia were sampled. IgM and IgG antibodies against WNV were detected in 1.6% (8/485; 95%IC: 0.0-2.5) and 61.9% (300/485; 95%IC: 58.3-65.5) of the unvaccinated individuals, respectively. The seropositivity in vaccinated horses was 86.6% (207/239). The main risk factors associated with WNV exposure in unvaccinated equids were the breed (crossbreed), the location of animals in spring-summer (outside), and the presence of natural water ponds close to the surveyed herds. The high individual seroprevalence obtained in the affected herds indicates that WNV circulation was more widespread than the reported by passive surveillance during the WNV epidemic in 2020. The re-emergence of WNV in 2020 in southern Spain evidenced the needed to improve integrated surveillance systems, minimizing the impact of future cases in equids and humans in high-risk areas.

Serological and molecular surveillance of West Nile virus in domesticated mammals of peninsular Malaysia

West Nile virus is a mosquito-borne neurotropic pathogen with a wide host range that constitutes a significant risk to public and animal health. There is limited information on WNV infection in domesticated mammals in Malaysia; however, current reports indicate infections in birds, macaques, bats and pigs from Malaysia. In this study, 203 serum samples from cattle, goats, and horses were tested for the presence of anti-WNV IgG using a competitive enzyme-linked immunosorbent assay (c-ELISA). Additionally, using one-step RT-PCR, nasopharyngeal swabs were analyzed for WNV RNA from all 203 animals in this study. The WNV seroprevalence was 32.53% (27/83) at 95% CI (0.2342-0.4319) in cattle, 48.27% (14/29) at 95% CI (0.3139-0.6557) in goats and 53.84% (49/91) at 95% CI (0.4366-0.6373) in horses. Cross-reactive JEV antibodies were detected in two cattle and 34 horses. None of the cattle or goats tested positive for WNV RT-PCR. Seven horses were positive for WNV RT-PCR, a molecular prevalence of 7.69% (7/91) at 95% CI (0.0353-0.1528). This is the first reported detection of WNV in domesticated mammals of Malaysia, a significant addition to the growing evidence that WNV is being transmitted from vectors to susceptible hosts in Malaysia.

Scoping review of Culex mosquito life history trait heterogeneity in response to temperature

BACKGROUND

Mosquitoes in the genus Culex are primary vectors in the US for West Nile virus (WNV) and other arboviruses. Climatic drivers such as temperature have differential effects on species-specific changes in mosquito range, distribution, and abundance, posing challenges for population modeling, disease forecasting, and subsequent public health decisions. Understanding these differences in underlying biological dynamics is crucial in the face of climate change.

METHODS

We collected empirical data on thermal response for immature development rate, egg viability, oviposition, survival to adulthood, and adult lifespan for Culex pipiens, Cx. quinquefasciatus, Cx. tarsalis, and Cx. restuans from existing literature according to the PRISMA scoping review guidelines.

RESULTS

We observed linear relationships with temperature for development rate and lifespan, and nonlinear relationships for survival and egg viability, with underlying variation between species. Optimal ranges and critical minima and maxima also appeared varied. To illustrate how model output can change with experimental input data from individual Culex species, we applied a modified equation for temperature-dependent mosquito type reproduction number for endemic spread of WNV among mosquitoes and observed different effects.

CONCLUSIONS

Current models often input theoretical parameters estimated from a single vector species; we show the need to implement the real-world heterogeneity in thermal response between species and present a useful data resource for researchers working toward that goal.

Characterisation of human exposure to nocturnal biting by malaria and arbovirus vectors in a rural community in Chókwè district, southern Mozambique

Background: Understanding the magnitude of human exposure to mosquito biting is fundamental to reduce pathogen transmission. Here we report on a study quantifying the levels of mosquitoes attacking humans throughout the night in a rural area of Southern Mozambique. Methods: Surveys were carried out in Massavasse village, southern Mozambique. The abundance and composition of host-seeking mosquito communities at night were assessed by human-landing catches (HLC) at one-hour intervals. Periods when people were located predominantly outdoors or indoors were used to estimate the amount of residents' exposure to mosquito bites in either location, to explore the potential impact a bed net could have had in reducing biting by each vector species. Results: A total of 69,758 host-seeking female mosquitoes comprising 23 species in four genera were collected. The exposure to biting by virtually all vector species was consistently high outdoors, typically at early evening and morning, with exception of An. gambiae s.l which was likely of biting a person with nearly same intensity indoors and outdoors throughout the night. Bed nets use could have reduced biting by An. gambiae s.l (dominated by An. arabiensis), Ma. africana, Ma. uniformis, Cx. pipiens, Cx. antennatus, and Cx. poicilipes by 53%, 47%, 46%, 38%, 31%, and 28% respectively, compared to non-users. Conversely, a bed net user would have had little protection against An. pharoensis, An. ziemanni, An. tenebrosus, and Cx. tritaeniorhynchus biting exposures. Conclusions: This study showed that Massavasse residents were exposed to high levels of outdoor biting by malaria and arbovirus vectors that abound in the village. The findings help to identify entomological drivers of persistent malaria transmission in Mozambique and identify a wide range of arbovirus vectors nocturnally active in rural areas, many with outbreak potential. The study highlights the need for a surveillance system for monitoring arboviral diseases vectors in Mozambique.

First Isolation and Genome Sequence Analysis of West Nile Virus in Mosquitoes in Brazil

West Nile virus is a flavivirus transmitted by mosquitoes, mainly of the genus Culex. In Brazil, serological studies have already indicated the circulation of the virus since 2003, with the first human case detected in 2014. The objective of the present paper is to report the first isolation of WNV in a Culex (Melanoconion) mosquito. Arthropods were collected by protected human attraction and CDC light bait, and taxonomically identified and analyzed by viral isolation, complement fixation and genomic sequencing tests. WNV was isolated from samples of Culex (Melanoconion) mosquitoes, and the sequencing analysis demonstrated that the isolated strain belonged to lineage 1a. The finding of the present study presents the first evidence of the isolation and genome sequencing of WNV in arthropods in Brazil.

Vector Competence of Culex quinquefasciatus from Brazil for West Nile Virus

West Nile virus is characterized as a neurotropic pathogen, which can cause West Nile fever and is transmitted by mosquitoes of the genus Culex. In 2018, the Instituto Evandro Chagas performed the first isolation of a WNV strain in Brazil from a horse brain sample. The present study aimed to evaluate the susceptibility of orally infected Cx. quinquefasciatus from the Amazon region of Brazil to become infected and transmit the WNV strain isolated in 2018. Oral infection was performed with blood meal artificially infected with WNV, followed by analysis of infection, dissemination, and transmission rates, as well as viral titers of body, head, and saliva samples. At the 21st dpi, the infection rate was 100%, the dissemination rate was 80%, and the transmission rate was 77%. These results indicate that Cx. quinquefasciatus is susceptible to oral infection by the Brazilian strain of WNV and may act as a possible vector of the virus since it was detected in saliva from the 21st dpi.

Eastern, Western, and Venezuelan Equine Encephalitis and West Nile Viruses: Clinical and Public Health Considerations

The continued recognition and emergence of alphavirus and flavivirus diseases is a growing veterinary and public health concern. As the global environment continues to change, mosquito-borne diseases will continue to evolve and expand. Continued development of readily available vaccines for the prevention of these diseases in humans and animals is essential to controlling epizootics of these diseases. Further research into effective antiviral treatments is also sorely needed. This article describes equine encephalitis viruses with a focus on clinical and public health considerations.

Meta-Viromic Sequencing Reveals Virome Characteristics of Mosquitoes and Culicoides on Zhoushan Island, China

Mosquitoes and biting Culicoides species are arbovirus vectors. Effective virome profile surveillance is essential for the prevention and control of insect-borne diseases. From June to September 2021, we collected eight species of female mosquito and Culicoides on Zhoushan Island, China, and used meta-viromic sequencing to analyze their virome compositions and characteristics. The classified virus reads were distributed in 191 genera in 66 families. The virus sequences in mosquitoes with the largest proportions were Iflaviridae (30.03%), Phasmaviridae (23.09%), Xinmoviridae (21.82%), Flaviviridae (13.44%), and Rhabdoviridae (8.40%). Single-strand RNA⁺ viruses formed the largest proportions of viruses in all samples. Blood meals indicated that blood-sucking mosquito hosts were mainly chicken, duck, pig, and human, broadly consistent with the habitats where the mosquitoes were collected. Novel viruses of the Orthobunyavirus, Narnavirus, and Iflavirus genera were found in Culicoides by de-novo assembly. The viruses with vertebrate hosts carried by mosquitoes and Culicoides also varied widely. The analysis of unclassified viruses and deep-learning analysis of the "dark matter" in the meta-viromic sequencing data revealed the presence of a large number of unknown viruses. IMPORTANCE The monitoring of the viromes of mosquitoes and Culicoides, widely distributed arbovirus transmission vectors, is crucial to evaluate the risk of infectious disease transmission. In this study, the compositions of the viromes of mosquitoes and Culicoides on Zhoushan Island varied widely and were related mainly to the host species, with different host species having different core viromes. and many unknown sequences in the Culicoides viromes remain to be annotated, suggesting the presence of a large number of unknown viruses.

Composition and global distribution of the mosquito virome - A comprehensive database of insect-specific viruses

Mosquitoes are vectors for emerging and re-emerging infectious viral diseases of humans, livestock and other animals. In addition to these arthropod-borne (arbo)viruses, mosquitoes are host to an array of insect-specific viruses, collectively referred to as the mosquito virome. Mapping the mosquito virome and understanding if and how its composition modulates arbovirus transmission is critical to understand arboviral disease emergence and outbreak dynamics. In recent years, next-generation sequencing as well as PCR and culture-based methods have been extensively used to identify mosquito-associated viruses, providing insights into virus ecology and evolution. Until now, the large amount of mosquito virome data, specifically those acquired by metagenomic sequencing, has not been comprehensively integrated. We have constructed a searchable database of insect-specific viruses associated with vector mosquitoes from 175 studies, published between October 2000 and February 2022. We identify the most frequently detected and widespread viruses of the Culex, Aedes and Anopheles mosquito genera and report their global distribution. In addition, we highlight the challenges of extracting and integrating published virome data and we propose that a standardized reporting format will facilitate data interpretation and re-use by other scientists. We expect our comprehensive database, summarizing mosquito virome data collected over 20 years, to be a useful resource for future studies.

Detection of West Nile Virus Lineage 2 in Eastern Romania and First Identification of Sindbis Virus RNA in Mosquitoes Analyzed using High-Throughput Microfluidic Real-Time PCR

The impact of mosquito-borne diseases on human and veterinary health is being exacerbated by rapid environmental changes caused mainly by changing climatic patterns and globalization. To gain insight into mosquito-borne virus circulation from two counties in eastern and southeastern Romania, we have used a combination of sampling methods in natural, urban and peri-urban sites. The presence of 37 mosquito-borne viruses in 16,827 pooled mosquitoes was analyzed using a high-throughput microfluidic real-time PCR assay. West Nile virus (WNV) was detected in 10/365 pools of Culex pipiens (n = 8), Culex modestus (n = 1) and Aedes vexans (n = 1) from both studied counties. We also report the first molecular detection of Sindbis virus (SINV) RNA in the country in one pool of Culex modestus. WNV infection was confirmed by real-time RT-PCR (10/10) and virus isolation on Vero or C6/36 cells (four samples). For the SINV-positive pool, no cytopathic effectwas observed after infection of Vero or C6/36 cells, but no amplification was obtained in conventional SINV RT-PCR. Phylogenetic analysis of WNV partial NS5 sequences revealed that WNV lineage 2 of theCentral-Southeast European clade, has a wider circulation in Romania than previously known.

Whole genome sequencing and phylogenetic analysis of West Nile viruses from animals in New England, United States, 2021

West Nile virus is a mosquito-borne Flavivirus which is the leading cause of global arboviral encephalitis. We sequenced WNVs from an American crow found in Connecticut and an alpaca found in Massachusetts which were submitted to the Connecticut Veterinary Medical Diagnostic Laboratory (CVMDL). We report here the complete protein-coding sequences (CDS) of the WNVs (WNV 21-3957/USA CT/Crow/2021 and WNV 21-3782/USA MA/Alpaca/2021) and their phylogenetic relationship with other WNVs recovered from across the United States. In the phylogenetic analysis, the WNVs from this study belonged to the WNV lineage 1. The WNV 21-3957/USA CT/Crow/2021 clustered with WNVs from a mosquito and birds in New York during 2007-2013. Interestingly, the virus detected in the alpaca, WNV 21-3782/USA MA/Alpaca/2021 clustered with WNVs from mosquitos in New York, Texas, and Arizona during 2012-2016. The genetic differences between the viruses detected during the same season in an American crow and an alpaca suggest that vector-host feeding preferences are most likely driving viral transmission. The CDS of the WNVs and their phylogenetic relationships with other WNVs established in this study would be useful as reference data for future investigations on WNVs. Seasonal surveillance of WNV in birds and mammals and the genetic characterization of detected viruses are necessary to monitor patterns of disease presentations and viral evolution within a geographical area.

Serosurvey in Two Dengue Hyperendemic Areas of Costa Rica Evidence Active Circulation of WNV and SLEV in Peri-Domestic and Domestic Animals and in Humans

Costa Rica harbors several flaviviruses, including Dengue (DENV), Zika (ZIKV), West Nile virus (WNV), and Saint Louis encephalitis virus (SLEV). While DENV and ZIKV are hyperendemic, previous research indicates restricted circulation of SLEV and WNV in animals. SLEV and WNV seroprevalence and high transmission areas have not yet been measured. To determine the extents of putative WNV and SLEV circulation, we sampled peri-domestic and domestic animals, humans, and mosquitoes in rural households located in two DENV and ZIKV hyperendemic regions during the rainy and dry seasons of 2017-2018 and conducted plaque reduction neutralization test assay for serology (PRNT) and RT-PCR for virus detection. In Cuajiniquil, serological evidence of WNV and SLEV was found in equines, humans, chickens, and wild birds. Additionally, five seroconversion events were recorded for WNV (2 equines), SLEV (1 human), and DENV-1 (2 humans). In Talamanca, WNV was not found, but serological evidence of SLEV circulation was recorded in equines, humans, and wild birds. Even though no active viral infection was detected, the seroconversion events recorded here indicate recent circulation of SLEV and WNV in these two regions. This study thus provides clear-cut evidence for WNV and SLEV presence in these areas, and therefore, they should be considered in arboviruses differential diagnostics and future infection prevention campaigns.

Culex Mosquito Piwi4 Is Antiviral against Two Negative-Sense RNA Viruses

Culex spp. mosquitoes transmit several pathogens concerning public health, including West Nile virus and Saint Louis encephalitis virus. Understanding the antiviral immune system of Culex spp. mosquitoes is important for reducing the transmission of these viruses. Mosquitoes rely on RNA interference (RNAi) to control viral replication. While the siRNA pathway in mosquitoes is heavily studied, less is known about the piRNA pathway. The piRNA pathway in mosquitoes has recently been connected to mosquito antiviral immunity. In Aedes aegypti, Piwi4 has been implicated in antiviral responses. The antiviral role of the piRNA pathway in Culex spp. mosquitoes is understudied compared to Ae. aegypti. Here, we aimed to identify the role of PIWI genes and piRNAs in Culex quinquefasciatus and Culex tarsalis cells during virus infection. We examined the effect of PIWI gene silencing on virus replication of two arboviruses and three insect-specific viruses in Cx. quinquefasciatus derived cells (Hsu) and Cx. tarsalis derived (CT) cells. We show that Piwi4 is antiviral against the La Crosse orthobunyavirus (LACV) in Hsu and CT cells, and the insect-specific rhabdovirus Merida virus (MERDV) in Hsu cells. None of the silenced PIWI genes impacted replication of the two flaviviruses Usutu virus (USUV) and Calbertado virus, or the phasivirus Phasi-Charoen-like virus. We further used small RNA sequencing to determine that LACV-derived piRNAs, but not USUV-derived piRNAs were generated in Hsu cells and that PIWI gene silencing resulted in a small reduction in vpiRNAs. Finally, we determined that LACV-derived DNA was produced in Hsu cells during infection, but whether this viral DNA is required for vpiRNA production remains unclear. Overall, we expanded our knowledge on the piRNA pathway and how it relates to the antiviral response in Culex spp mosquitoes.

Characterization of the Blood-Feeding Patterns of Culex quinquefasciatus (Diptera: Culicidae) in San Bernardino County, California

West Nile virus (WNV) is a zoonotic disease that is endemic in North America and is known to cause a range of symptoms from mild to life threatening in humans. Culex quinquefasciatus is one of the most prominent vectors of WNV in Southern California. The goal of this study was to identify which animal species are most fed upon by these mosquitoes in various habitats in the West Valley area of San Bernardino County, California, and determine the relationship between blood-feeding patterns and WNV activity in the region. Culex quinquefasciatus specimens were collected by West Valley Mosquito and Vector Control District during 2011 from 32 different sites. The bloodmeals of 683 individuals (92.4% of those tested) were identified using the mitochondrial gene cytochrome c oxidase 1 (COI). These bloodmeals comprised 29 vertebrate species across four different habitats. Species richness (ranging from 10 to 17) was not significantly different between habitats when rarified to account for sample size. Across habitats, the highest percentage of avian bloodmeals were taken from house sparrows (18.8-39.1%) and house finches (2.6-31.5%). Bloodmeals were identified from five mammalian species, accounting for 5.1-59.2% of bloodmeals by habitat, including humans (0-4.1%). A seasonal shift towards increased mammalian bloodmeal prevalence, specifically for domestic dog and human bloodmeals, was observed in urban habitats. The WNV activity during 2011 in San Bernardino County occurred mostly in urban and suburban areas as indicated by minimum infection rate (MIR) in Culex quinquefasciatus, notable as all human bloodmeals were identified from these two habitats.

West Nile virus: another emerging arboviral risk for travelers?

Purpose of Review

West Nile virus (WNV) is an arbovirus transmitted by mosquitos of the genus Culex. Manifestations of WNV infection range from asymptomatic to devastating neuroinvasive disease leading to flaccid paralysis and death. This review examines WNV epidemiology and ecology, with an emphasis on travel-associated infection.

Recent Findings

WNV is widespread, including North America and Europe, where its range has expanded in the past decade. Rising temperatures in temperate regions are predicted to lead to an increased abundance of Culex mosquitoes and an increase in their ability to transmit WNV. Although the epidemiologic patterns of WNV appear variable, its geographic distribution most certainly will continue to increase. Travelers are at risk for WNV infection and its complications. Literature review identified 39 cases of documented travel-related WNV disease, the majority of which resulted in adverse outcomes, such as neuroinvasive disease, prolonged recovery period, or death.

Summary

The prediction of WNV risk is challenging due to the complex interactions of vector, pathogen, host, and environment. Travelers planning to visit endemic areas should be advised regarding WNV risk and mosquito bite prevention. Evaluation of ill travelers with compatible symptoms should consider the diagnosis of WNV for those visiting in endemic areas as well as for those returning from destinations with known WNV circulation.

Seroepidemiological Survey of West Nile Virus Infections in Horses from Berlin/Brandenburg and North Rhine-Westphalia, Germany

Following the introduction of the West Nile virus (WNV) into eastern Germany in 2018, increasing infections have been diagnosed in birds, equines, and humans over time, while the spread of WNV into western Germany remained unclear. We screened 437 equine sera from 2018 to 2020, excluding vaccinated horses, collected from convenience sampled patients in the eastern and western parts of Germany, for WNV-specific antibodies (ELISAs followed by virus/specific neutralization tests) and genomes (RT-qPCRs). Clinical presentations, final diagnoses, and demographic data were also recorded. In the eastern part, a total of eight horses were found WNV seropositive in 2019 (seroprevalence of 8.16%) and 27 in 2020 (13.77%). There were also two clinically unsuspected horses with WNV-specific antibodies in the western part from 2020 (2.63%), albeit travel history-related infections could not be excluded. None of the horse sera contained WNV-specific genomes. Eight horses in eastern Germany carried WNV-IgM antibodies, but only four of these showed typical clinical signs. These results underline the difficulty of detecting a WNV infection in a horse solely based on clinical signs. Thus, WNV circulation is established in the horse population in eastern Germany, but not yet in the western part.

West Nile virus in Spain: Forecasting the geographical distribution of risky areas with an ecological niche modelling approach

West Nile virus (WNV), a well-known emerging vector-borne arbovirus with a zoonotic life cycle, represents a threat to both public and animal health. Transmitted by ornithophilic mosquitoes, its transmission is difficult to predict and even more difficult to prevent. The massive and unprecedented number of human cases and equid outbreaks in Spain during 2020 interpellates for new approaches. For the first time, we present an integrate analysis from a niche perspective to provide an insight to the situation of West Nile disease (WND) in Spain. Our modelling approach benefits from the combined use of global occurrence records of outbreaks of WND in equids and of its two alleged main vectors in Spain, Culex pipiens and Cx. perexiguus. Maps of the climatic suitability for the presence of the two vectors species and for the circulation of WNV are provided. The main outcome of our study is a map delineating the areas under certain climatic risk of transmission. Our analyses indicate that the climatic risk of transmission of WND is medium in areas nearby the south Atlantic coastal area of the Cadiz Gulf and the Mediterranean coast, and high in southwestern Spain. The higher risk of transmission in the basins of the rivers Guadiana and Guadalquivir cannot be attributed exclusively to the local abundance of Cx. pipiens, but could be ascribed to the presence and abundance of Cx. perexiguus. Furthermore, this integrated analysis suggests that the WNV presents an ecological niche of its own, not fully overlapping the ones of its hosts or vector, and thus requiring particular environmental conditions to succeed in its infection cycle.

Shifting From Sectoral to Integrated Surveillance by Changing Collaborative Practices: Application to West Nile Virus Surveillance in a Small Island State of the Caribbean

After spreading in the Americas, West Nile virus was detected in Guadeloupe (French West Indies) for the first time in 2002. Ever since, several organizations have conducted research, serological surveys, and surveillance activities to detect the virus in horses, birds, mosquitoes, and humans. Organizations often carried them out independently, leading to knowledge gaps within the current virus' situation. Nearly 20 years after the first evidence of West Nile virus in the archipelago, it has not yet been isolated, its impact on human and animal populations is unknown, and its local epidemiological cycle is still poorly understood. Within the framework of a pilot project started in Guadeloupe in 2019, West Nile virus was chosen as a federative model to apply the "One Health" approach for zoonotic epidemiological surveillance and shift from a sectorial to an integrated surveillance system. Human, animal, and environmental health actors involved in both research and surveillance were considered. Semi-directed interviews and a Social Network Analysis were carried out to learn about the surveillance network structure and actors, analyze information flows, and identify communication challenges. An information system was developed to fill major gaps: users' needs and main functionalities were defined through a participatory process where actors also tested and validated the tool. Additionally, all actors shared their data, which were digitized, cataloged, and centralized, to be analyzed later. An R Shiny server was integrated into the information system, allowing an accessible and dynamic display of data showcasing all of the partners' information. Finally, a series of virtual workshops were organized among actors to discuss preliminary results and plan the next steps to improve West Nile Virus and vector-borne or emerging zoonosis surveillance. The actors are willing to build a more resilient and cooperative network in Guadeloupe with improved relevance, efficiency, and effectiveness of their work.

Vector Surveillance, Host Species Richness, and Demographic Factors as West Nile Disease Risk Indicators

West Nile virus (WNV) is the most common arthropod-borne virus (arbovirus) in the United States (US) and is the leading cause of viral encephalitis in the country. The virus has affected tens of thousands of US persons total since its 1999 North America introduction, with thousands of new infections reported annually. Approximately 1% of humans infected with WNV acquire neuroinvasive West Nile Disease (WND) with severe encephalitis and risk of death. Research describing WNV ecology is needed to improve public health surveillance, monitoring, and risk assessment. We applied Bayesian joint-spatiotemporal modeling to assess the association of vector surveillance data, host species richness, and a variety of other environmental and socioeconomic disease risk factors with neuroinvasive WND throughout the conterminous US. Our research revealed that an aging human population was the strongest disease indicator, but climatic and vector-host biotic interactions were also significant in determining risk of neuroinvasive WND. Our analysis also identified a geographic region of disproportionately high neuroinvasive WND disease risk that parallels the Continental Divide, and extends southward from the US-Canada border in the states of Montana, North Dakota, and Wisconsin to the US-Mexico border in western Texas. Our results aid in unraveling complex WNV ecology and can be applied to prioritize disease surveillance locations and risk assessment.

Pathogenicity and virulence of West Nile virus revisited eight decades after its first isolation

West Nile virus (WNV) is a flavivirus which transmission cycle is maintained between mosquitoes and birds, although it occasionally causes sporadic outbreaks in horses and humans that can result in serious diseases and even death. Since its first isolation in Africa in 1937, WNV had been considered a neglected pathogen until its recent spread throughout Europe and the colonization of America, regions where it continues to cause outbreaks with severe neurological consequences in humans and horses. Although our knowledge about the characteristics and consequences of the virus has increased enormously lately, many questions remain to be resolved. Here, we thoroughly update our knowledge of different aspects of the WNV life cycle: virology and molecular classification, host cell interactions, transmission dynamics, host range, epidemiology and surveillance, immune response, clinical presentations, pathogenesis, diagnosis, prophylaxis (antivirals and vaccines), and prevention, and we highlight those aspects that are still unknown and that undoubtedly require further investigation.

Simultaneous circulation of two West Nile virus lineage 2 clades and Bagaza virus in the Zambezi region, Namibia

Flaviviruses include a great diversity of mosquito-borne arboviruses with epidemic potential and high global disease burden. Several flaviviruses are circulating in southern Africa affecting humans and livestock, among them West Nile virus (WNV) and Wesselsbron virus. Despite their high relevance, no arbovirus surveillance study has been conducted for more than 35 years in Namibia. In this study we assessed the diversity of flaviviruses circulating in mosquitoes in the densely populated, semi-tropical Zambezi region of north-eastern Namibia. In total, 10,206 mosquitoes were sampled in Bwabwata and Mudumu national parks and Mashi and Wuparo conservancies and screened for flavivirus infections. A high infection rate with insect-specific flaviviruses was found with 241 strains of two previously known and seven putative novel insect-specific flaviviruses. In addition, we identified ten strains of WNV in the main vector Cx. univittatus sampled in the Mashi conservancy. Surprisingly, the strains fell into two different clades of lineage 2, 2b and 2d. Further, three strains of Bagaza Virus (BAGV) were found in Cx. univittatus mosquitoes originating from Mudumu national park. Assessment of BAGV growth in different cell lines showed high replication rates in mosquito and duck cells and about 100,000fold lower replication in human, primate and rodent cells. We demonstrate a wide genetic diversity of flaviviruses is circulating in mosquitoes in the Zambezi region. Importantly, WNV and BAGV can cause outbreaks including severe disease and mortality in humans and birds, respectively. Future studies should focus on WNV and BAGV geographic distribution, as well as on their potential health impacts in and the associated social and economic implications for southern Africa.

Mosquitoes serve as vectors for the transmission of infectious diseases. Some of the most important mosquito-borne arboviruses belong to the genus Flavivirus, which can induce severe disease in humans and livestock. Surveillance of vector populations provide information on circulating arboviruses and may help to identify local outbreaks. Here we sampled mosquitoes over three wet seasons in the densely populated, semi-tropical Zambezi region of north-eastern Namibia and tested them for infections with flaviviruses. We observed simultaneous circulation of two different West Nile virus clades in the main vector species Cx. univittatus. Humans infected with West Nile virus can develop flu-like symptoms or in rare cases meningoencephalitis. Further, we detected Bagaza virus in Cx. univittatus from another locality and season. Bagaza virus infects birds leading to high mortality rates and may also infect humans. Our data suggest that both viruses are endemic in the Zambezi region and may affect human health and well-being in Namibia.

Dose dependence of susceptibility and transmission for an Argentinean West Nile virus strain in local Culex pipiens quinquefasciatus (Diptera: Culicidae)

BACKGROUND

West Nile virus (WNV) activity has been documented in the central region of Argentina since 2005, but its maintenance network has not been elucidated yet.

METHODS

We evaluated the susceptibility to WNV oral infection and transmission in a Culex pipiens quinquefasciatus mosquito population by means of a dose-dependent vector competence assay. Mosquitoes were orally infected with five different viral loads and evaluated for viral infection, dissemination and transmission.

RESULTS

The evaluated population was susceptible to WNV oral infection. Disseminated infections were detected in all the viral doses but transmission was only detected in the higher doses (6 and 7 log10 plaque-forming units/ml). A linear relationship between doses and transmission rates could be established.

CONCLUSIONS

A minimum transmission threshold suggests that the Cu. p. quinquefasciatus from Argentina could acquire WNV infection from local urban birds and transmit the virus.

Epidemiology and Clinical Presentation of West Nile Virus Infection in Horses in South Africa, 2016-2017

Although West Nile virus (WNV) is endemic to South Africa (RSA), it has only become recognized as a significant cause of neurological disease in humans and horses locally in the past 2 decades, as it emerged globally. This article describes the epidemiological and clinical presentation of WNV in horses across RSA during 2016–2017. In total, 54 WNV-positive cases were identified by passive surveillance in horses with febrile and/or neurological signs at the Centre for Viral Zoonoses, University of Pretoria. They were followed up and compared to 120 randomly selected WNV-negative controls with the same case definition and during the same time period. Of the WNV-positive cases, 52% had fever, 92% displayed neurological signs, and 39% experienced mortality. Cases occurred mostly in WNV-unvaccinated horses <5 years old, during late summer and autumn after heavy rain, in the temperate to warm eastern parts of RSA. WNV-positive cases that had only neurological signs without fever were more likely to die. In the multivariable analysis, the odds of WNV infection were associated with season (late summer), higher altitude, more highly purebred animals, younger age, and failure to vaccinate against WNV. Vaccination is currently the most effective prophylactic measure to reduce WNV morbidity and mortality in horses.

Molecular Analysis of the Bloodmeals of Culex spp. Mosquitoes at Natural Habitats in Singapore to Investigate the Potential Risk of Japanese Encephalitis Virus and West Nile Virus Transmission

Japanese encephalitis virus (JEV) and West Nile virus (WNV) are arboviruses primarily transmitted by Culex spp. mosquitoes. Birds are the primary hosts for JEV and WNV. Recent WNV outbreaks in Europe and United States and their association with migratory birds highlight the importance of understanding the feeding host preference of potential vectors for outbreak preparedness, especially in nonendemic settings. Singapore is nonendemic to JEV and WNV, but is a stopover site for migratory birds of the East Asian-Australasian Flyway. Therefore, we elucidated the feeding host range of Culex spp. mosquitoes captured in four natural (bird) habitats in Singapore from January 2011 to December 2012. We characterized feeding host DNA in field-caught mosquitoes using a PCR sequencing-based assay targeting the mitochondrial gene regions. Of 22,648 mosquitoes captured, 21,287 belonged to the Culex vishnui subgroup. The host DNA analysis showed that mosquitoes from the Cx. vishnui subgroup are opportunistic biters, feeding on a range of birds and mammals. Cx. vishnui subgroup, Culex sitiens and Culex bitaeniorhynchus, was primarily ornithophagic, although they fed opportunistically on mammals, including humans. Culex gelidus and Culex quinquefasciatus, in contrast, fed mainly on mammals. The presence of ornitho- and anthropophilic mosquito vectors and susceptible avian and mammalian hosts poses a risk spill-over transmission of JEV and WNV among humans, should these viruses be introduced through migratory birds and establish persistent transmission in resident birds and animal hosts in Singapore.

A Hyperactive Kunjin Virus NS3 Helicase Mutant Demonstrates Increased Dissemination and Mortality in Mosquitoes

The unwinding of double-stranded RNA intermediates is critical for the replication and packaging of flavivirus RNA genomes. This unwinding activity is achieved by the ATP-dependent nonstructural protein 3 (NS3) helicase. In previous studies, we investigated the mechanism of energy transduction between the ATP and RNA binding pockets using molecular dynamics simulations and enzymatic characterization. Our data corroborated the hypothesis that motif V is a communication hub for this energy transduction. More specifically, mutations T407A and S411A in motif V exhibit a hyperactive helicase phenotype, leading to the regulation of translocation and unwinding during replication. However, the effect of these mutations on viral infection in cell culture and in vivo is not well understood. Here, we investigated the role of motif V in viral replication using West Nile virus (Kunjin subtype) T407A and S411A mutants (T407A and S411A Kunjin, respectively) in cell culture and in vivo We were able to recover S411A Kunjin but unable to recover T407A Kunjin. Our results indicated that S411A Kunjin decreased viral infection and increased cytopathogenicity in cell culture compared to wild-type (WT) Kunjin. Similarly, decreased infection rates in surviving S411A Kunjin-infected Culex quinquefasciatus mosquitoes were observed, but S411A Kunjin infection resulted in increased mortality compared to WT Kunjin infection. Additionally, S411A Kunjin infection increased viral dissemination and saliva positivity rates in surviving mosquitoes compared to WT Kunjin infection. These data suggest that S411A Kunjin increases viral pathogenesis in mosquitoes. Overall, these data indicate that NS3 motif V may play a role in the pathogenesis, dissemination, and transmission efficiency of Kunjin virus.IMPORTANCE Kunjin and West Nile viruses belong to the arthropod-borne flaviviruses, which can result in severe symptoms, including encephalitis, meningitis, and death. Flaviviruses have expanded into new populations and emerged as novel pathogens repeatedly in recent years, demonstrating that they remain a global threat. Currently, there are no approved antiviral therapeutics against either Kunjin or West Nile viruses. Thus, there is a pressing need for understanding the pathogenesis of these viruses in humans. In this study, we investigated the role of the Kunjin virus helicase on infection in cell culture and in vivo This work provides new insight into how flaviviruses control pathogenesis and mosquito transmission through the nonstructural protein 3 helicase.

Beyond HIV infection: Neglected and varied impacts of CCR5 and CCR5Δ32 on viral diseases

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CCR5 regulates multiple cell types (e.g., T regulatory and Natural Killer cells) and immune responses.

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The effects of CCR5, CCR5Δ32 (variant associated with reduced CCR5 expression) and CCR5 antagonists vary between infections.

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CCR5 affects the pathogenesis of flaviviruses, especially in the brain.

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The genetic variant CCR5Δ32 increases the risk of symptomatic West Nile virus infection.

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The triad “CCR5, extracellular vesicles and infections” is an emerging topic.

The interactions between chemokine receptors and their ligands may affect susceptibility to infectious diseases as well as their clinical manifestations. These interactions mediate both the traffic of inflammatory cells and virus-associated immune responses. In the context of viral infections, the human C-C chemokine receptor type 5 (CCR5) receives great attention from the scientific community due to its role as an HIV-1 co-receptor. The genetic variant CCR5Δ32 (32 base-pair deletion in CCR5 gene) impairs CCR5 expression on the cell surface and is associated with protection against HIV infection in homozygous individuals. Also, the genetic variant CCR5Δ32 modifies the CCR5-mediated inflammatory responses in various conditions, such as inflammatory and infectious diseases. CCR5 antagonists mimic, at least in part, the natural effects of the CCR5Δ32 in humans, which explains the growing interest in the potential benefits of using CCR5 modulators for the treatment of different diseases. Nevertheless, beyond HIV infection, understanding the effects of the CCR5Δ32 variant in multiple viral infections is essential to shed light on the potential effects of the CCR5 modulators from a broader perspective. In this context, this review discusses the involvement of CCR5 and the effects of the CCR5Δ32 in human infections caused by the following pathogens: West Nile virus, Influenza virus, Human papillomavirus, Hepatitis B virus, Hepatitis C virus, Poliovirus, Dengue virus, Human cytomegalovirus, Crimean-Congo hemorrhagic fever virus, Enterovirus, Japanese encephalitis virus, and Hantavirus. Subsequently, this review addresses the impacts of CCR5 gene editing and CCR5 modulation on health and viral diseases. Also, this article connects recent findings regarding extracellular vesicles (e.g., exosomes), viruses, and CCR5. Neglected and emerging topics in “CCR5 research” are briefly described, with focus on Rocio virus, Zika virus, Epstein-Barr virus, and Rhinovirus. Finally, the potential influence of CCR5 on the immune responses to coronaviruses is discussed.

A Comparison of Adult Mosquito Trapping Methods to Assess Potential West Nile Virus Mosquito Vectors in Greece during the Onset of the 2018 Transmission Season

West Nile virus (WNV) threatens the health of humans and equines worldwide. Culex (Cx.) pipiens complex mosquitoes are major vectors but numerous other species have been implicated. Due to variations in blood-feeding behaviour, Cx. pipiens biotypes and hybrids influence transmission, from enzootic cycles (between mosquitoes and birds), to spill-over transmission to humans and equines. In this study, mosquitoes were collected in May–June 2018 during the early period of the transmission season from two regional units of Greece, where WNV cases had been reported in the previous four years (Palaio Faliro and Argolida). A total of 1062 mosquitoes were collected with Biogents Sentinel 2 traps collecting both a greater number of all mosquito species and the Cx. pipiens complex than CDC miniature light traps or Heavy Duty EVS traps. Molecular identification confirmed additional species including Aedes albopictus. The proportion of Cx. pipiens biotypes in Palaio Faliro was 54.5% pipiens, 20.0% molestus and 25.5% hybrids. In Argolida, the collection comprised 68.1% pipiens biotype, 8.3% molestus biotype and 23.6% hybrids. Screening resulted in WNV detection in three females of the pipiens biotype and in one hybrid. As hybrids play a role in spill-over transmission, these findings highlight the importance of entomological surveillance programs incorporating molecular xenomonitoring as an early warning before human cases at the onset of the transmission season.

Insecticide resistance genes affect Culex quinquefasciatus vector competence for West Nile virus

Insecticide resistance has been reported to impact the interactions between mosquitoes and the pathogens they transmit. However, the effect on vector competence for arboviruses still remained to be investigated. We examined the influence of two insecticide resistance mechanisms on vector competence of the mosquito Culex quinquefasciatus for two arboviruses, Rift Valley Fever virus (RVFV) and West Nile virus (WNV). Three Cx. quinquefasciatus lines sharing a common genetic background were used: two insecticide-resistant lines, one homozygous for amplification of the Ester² locus (SA2), the other homozygous for the acetylcholinesterase ace-1 G119S mutation (SR) and the insecticide-susceptible reference line Slab. Statistical analyses revealed no significant effect of insecticide-resistant mechanisms on vector competence for RVFV. However, both insecticide resistance mechanisms significantly influenced the outcome of WNV infections by increasing the dissemination of WNV in the mosquito body, therefore leading to an increase in transmission efficiency by resistant mosquitoes. These results showed that insecticide resistance mechanisms enhanced vector competence for WNV and may have a significant impact on transmission dynamics of arboviruses. Our findings highlight the importance of understanding the impacts of insecticide resistance on the vectorial capacity parameters to assess the overall consequence on transmission.

Plant-Derived Essential Oils; Their Larvicidal Properties and Potential Application for Control of Mosquito-Borne Diseases

Mosquito-borne diseases are currently considered as important threats to human health in subtropical and tropical regions. Resistance to synthetic larvicides in different species of mosquitoes, as well as environmental pollution, are the most common adverse effects of excessive use of such agents. Plant-derived essential oils (EOs) with various chemical entities have a lower chance of developing resistance. So far, no proper classification based on lethal concentration at 50% (LC₅₀) has been made for the larvicidal activity of EOs against different species of Aedes, Anopheles and Culex mosquitoes. To better understand the problem, a summary of the most common mosquito-borne diseases have been made. Related articles were gathered, and required information such as scientific name, used part(s) of plant, target species and LC₅₀ values were extracted. 411 LC₅₀ values were found about the larvicidal activity of EOs against different species of mosquitoes. Depending on the obtained results in each species, LC₅₀ values were summarized as follows: 24 EOs with LC₅₀ < 10 µg/mL, 149 EOs with LC₅₀ in range of 10- 50 µg/mL, 143 EOs having LC₅₀ within 50- 100 µg/mL and 95 EOs showing LC₅₀ > 100 µg/mL. EOs of Callitris glaucophylla and Piper betle against Ae. aegypti, Tagetes minuta against An. gambiae, and Cananga odorata against Cx. quinquefasciatus and An. dirus having LC₅₀ of ~ 1 µg/mL were potentially comparable to synthetic larvicides. It appears that these plants could be considered as candidates for botanical larvicides.

Evidence for West Nile Virus and Usutu Virus Infections in Wild and Resident Birds in Germany, 2017 and 2018

Wild birds play an important role as reservoir hosts and vectors for zoonotic arboviruses and foster their spread. Usutu virus (USUV) has been circulating endemically in Germany since 2011, while West Nile virus (WNV) was first diagnosed in several bird species and horses in 2018. In 2017 and 2018, we screened 1709 live wild and zoo birds with real-time polymerase chain reaction and serological assays. Moreover, organ samples from bird carcasses submitted in 2017 were investigated. Overall, 57 blood samples of the live birds (2017 and 2018), and 100 organ samples of dead birds (2017) were positive for USUV-RNA, while no WNV-RNA-positive sample was found. Phylogenetic analysis revealed the first detection of USUV lineage Europe 2 in Germany and the spread of USUV lineages Europe 3 and Africa 3 towards Northern Germany. USUV antibody prevalence rates were high in Eastern Germany in both years. On the contrary, in Northern Germany, high seroprevalence rates were first detected in 2018, with the first emergence of USUV in this region. Interestingly, high WNV-specific neutralizing antibody titers were observed in resident and short-distance migratory birds in Eastern Germany in 2018, indicating the first signs of a local WNV circulation.

Management of arthropod vector data - Social and ecological dynamics facing the One Health perspective

Emerging infectious diseases (EIDs) are spread by direct and/or indirect contacts between a pathogen or parasite and their hosts. Arthropod vectors have evolved as excellent bloodsuckers, providing an elegant transportation mode for a wide number of infectious agents. The nature of pathogen and parasite transfer and the models used to predict how a disease might spread are magnified in complexity when an arthropod vector is part of the disease cycle. One Health is a worldwide strategy for expanding interdisciplinary collaborations and communications in all aspects of health care for humans, animals and the environment. It would benefit from a structured analysis to address vectoring of arthropod-borne diseases as a dynamic transactional process. This review focused on how arthropod vector data can be used to better model and predict zoonotic disease outbreaks. With enhanced knowledge to describe arthropod vector disease transfer, researchers will have a better understanding about how to model disease outbreaks. As public health research evolves to include more social-ecological systems, the roles of society, ecology, epidemiology, pathogen/parasite evolution and animal behavior can be better captured in the research design. Overall, because of more collaborative data collection processes on arthropod vectors, disease modeling can better predict conditions where EIDs will occur.

West Nile Virus and Usutu Virus Monitoring of Wild Birds in Germany

By systematically setting up a unique nation-wide wild bird surveillance network, we monitored migratory and resident birds for zoonotic arthropod-borne virus infections, such as the flaviviruses West Nile virus (WNV) and Usutu virus (USUV). More than 1900 wild bird blood samples, from 20 orders and 136 different bird species, were collected between 2014 and 2016. Samples were investigated by WNV and USUV-specific real-time polymerase chain reactions as well as by differentiating virus neutralization tests. Dead bird surveillance data, obtained from organ investigations in 2016, were also included. WNV-specific RNA was not detected, whereas four wild bird blood samples tested positive for USUV-specific RNA. Additionally, 73 USUV-positive birds were detected in the 2016 dead bird surveillance. WNV neutralizing antibodies were predominantly found in long-distance, partial and short-distance migrants, while USUV neutralizing antibodies were mainly detected in resident wild bird species, preferentially with low seroprevalences. To date, WNV-specific RNA has neither been detected in wild birds, nor in mosquitoes, thus, we conclude that WNV is not yet present in Germany. Continued wild bird and mosquito monitoring studies are essential to detect the incursion of zoonotic viruses and to allow risk assessments for zoonotic pathogens.

Flaviviruses Produce a Subgenomic Flaviviral RNA That Enhances Mosquito Transmission

Mosquito-borne flaviviruses (MBFVs) are a global public health burden. MBFVs have several unique 3'UTR structures that inhibit the host RNA decay machinery to produce subgenomic flaviviral RNAs (sfRNAs). Number of sfRNA species and their relative quantities are dependent on the 3'UTR tertiary structures and can vary between tissues. Two recent in vivo studies demonstrated that sfRNA enhances mosquito transmission, resulting in increased infection rate of saliva. Transmission efficiency is determined by the immune response. First evidence points to sfRNA interference with the Toll and RNAi immune pathways. However, a more complex picture that includes flexibility in sfRNA production and interaction with immune-related proteins remains to be explored.