Monitoring West Nile virus (WNV) infection in wild birds in Serbia during 2012: first isolation and characterisation of WNV strains from Serbia

First Detection of West Nile Virus Lineage 2 in Culex pipiens Vectors in Croatia

The West Nile virus (WNV) has recently become more widespread, posing a threat to both human and animal health. In Western Europe, most outbreaks have been caused by WNV lineage 1, while in Eastern Europe, WNV lineage 2 has led to human and bird mortality. The ability to appropriately manage this threat is dependent on integrated surveillance and early detection. This study aimed to quantify the prevalence of WNV infection in mosquitoes and to identify the circulating viral lineage in eastern Croatia. Mosquito traps were set up in rural and urban areas during the 2021-2023 seasons, and the collected specimens were identified morphologically. Mosquito species Culex pipiens and Aedes albopictus were tested for Flaviviruses using conventional PCR in a heminested system. The positive samples were then subjected to a specific real-time PCR designed to detect WNV. A total of 385 mosquito pools were tested, and positive pools were found in samples from Osijek-Baranja and Vukovar-Srijem, both of which contained Cx. pipiens mosquitoes. Sequencing of amplicons revealed WNV lineage 2 partial NS5 gene sequences. Phylogenetic analysis suggests the Hungarian origin of strain, which complements birds' migratory routes. These findings indicate the first detection of WNV in mosquitoes in Croatia. This suggests that human cases in this region are likely due to infections with lineage 2 transmitted by local Culex mosquitoes.

Identification of West Nile virus RNA-dependent RNA polymerase non-nucleoside inhibitors by real-time high throughput fluorescence screening

West Nile virus (WNV) is a re-emergent mosquito-borne RNA virus that causes major outbreaks of encephalitis around the world. However, there is no therapeutic treatment to struggle against WNV, and the current treatment relies on alleviating symptoms. Therefore, due to the threat virus poses to animal and human health, there is an urgent need to come up with fast strategies to identify and assess effective antiviral compounds. A relevant target when developing drugs against RNA viruses is the viral RNA-dependent RNA polymerase (RdRp), responsible for the replication of the viral genome within a host cell. RdRps are key therapeutic targets based on their specificity for RNA and their essential role in the propagation of the infection. We have developed a fluorescence-based method to measure WNV RdRp activity in a fast and reliable real-time way. Interestingly, rilpivirine has shown in our assay inhibition of the WNV RdRp activity with an IC₅₀ value of 3.3 μM and its antiviral activity was confirmed in cell cultures. Furthermore, this method has been extended to build up a high-throughput screening platform to identify WNV polymerase inhibitors. By screening a small chemical library, novel RdRp inhibitors 1-4 have been identified. When their antiviral activity was tested against WNV in cell culture, 4 exhibited an EC₅₀ value of 2.5 μM and a selective index of 12.3. Thus, rilpivirine shows up as an interesting candidate for repurposing against flavivirus. Moreover, the here reported method allows the rapid identification of new WNV RdRp inhibitors.

Rapid spread of a new West Nile virus lineage 1 associated with increased risk of neuroinvasive disease during a large outbreak in northern Italy, 2022: One Health analysis

BACKGROUND

A new strain of WNV lineage 1 (WNV - 1) emerged in the Veneto Region, northern Italy, in 2021, eight years after the last outbreak of WNV - 1 in Italy. The virus, which co-circulates with WNV-2, has become endemic in the Region, where, in 2022, most human cases of neuroinvasive disease (WNND) reported in Europe have occurred.

METHODS

Comparative analysis of the epidemiology and clinical presentation of WNV-1 and WNV-2 infection in humans, as well as the temporal and geographic distribution of WNV-1 and WNV-2 among wild birds and Culex pipiens mosquitoes in Veneto, from May 16th to August 21st, 2022, to determine if the high number of WNND cases was associated with WNV-1.

RESULTS

As of August 21st, 2022, 222 human cases of WNV infection were confirmed by molecular testing, including 103 with fever (WNF) and 119 with WNND. WNV lineage was determined in 201 (90.5%) cases, comprising 138 WNV-1 and 63 WNV-2 infections. During the same period, 35 blood donors tested positive, including 30 in whom WNV lineage was determined (13 WNV-1 and 17 WNV-2). Comparative analysis of the distribution of WNV-1 and WNV-2 infections among WNND cases, WNF cases and WNV-positive blood donors showed that patients with WNND were more likely to have WNV-1 infection than blood donors (odds ratio 3.44; 95% CI 95% 1.54 to 8.24; p = 0.0043). As observed in humans, in wild birds WNV-1 had higher infectious rate (IR) and showed a more rapid expansion than WNV-2. At variance, the distribution of the two lineages was more even in mosquitoes, but with a trend of rapid increase of WNV-1 IR over WNV-2.

CONCLUSIONS

Comparative analysis of WNV-1 vs WNV-2 infection in humans, wild birds, and mosquitos showed a rapid expansion of WNV-1 and suggested that WNV-1 infected patients might have an increased risk to develop severe disease.

Artificial intelligence to predict West Nile virus outbreaks with eco-climatic drivers

Background

In Europe, the frequency, intensity, and geographic range of West Nile virus (WNV)-outbreaks have increased over the past decade, with a 7.2-fold increase in 2018 compared to 2017, and a markedly expanded geographic area compared to 2010. The reasons for this increase and range expansion remain largely unknown due to the complexity of the transmission pathways and underlying disease drivers. In a first, we use advanced artificial intelligence to disentangle the contribution of eco-climatic drivers to WNV-outbreaks across Europe using decade-long (2010-2019) data at high spatial resolution.

Methods

We use a high-performance machine learning classifier, XGBoost (eXtreme gradient boosting) combined with state-of-the-art XAI (eXplainable artificial intelligence) methodology to describe the predictive ability and contribution of different drivers of the emergence and transmission of WNV-outbreaks in Europe, respectively.

Findings

Our model, trained on 2010-2017 data achieved an AUC (area under the receiver operating characteristic curve) score of 0.97 and 0.93 when tested with 2018 and 2019 data, respectively, showing a high discriminatory power to classify a WNV-endemic area. Overall, positive summer/spring temperatures anomalies, lower water availability index (NDWI), and drier winter conditions were found to be the main determinants of WNV-outbreaks across Europe. The climate trends of the preceding year in combination with eco-climatic predictors of the first half of the year provided a robust predictive ability of the entire transmission season ahead of time. For the extraordinary 2018 outbreak year, relatively higher spring temperatures and the abundance of Culex mosquitoes were the strongest predictors, in addition to past climatic trends.

Interpretation

Our AI-based framework can be deployed to trigger rapid and timely alerts for active surveillance and vector control measures in order to intercept an imminent WNV-outbreak in Europe.

Funding

The work was partially funded by the Swedish Research Council FORMAS for the project ARBOPREVENT (grant agreement 2018-05973).

West Nile Virus Lineage 2 Spreads Westwards in Europe and Overwinters in North-Eastern Spain (2017–2020)

West Nile virus lineage 2 (WNV-L2) emerged in Europe in 2004; since then, it has spread across the continent, causing outbreaks in humans and animals. During 2017 and 2020, WNV-L2 was detected and isolated from four northern goshawks in two provinces of Catalonia (north-eastern Spain). In order to characterise the first Spanish WNV-L2 isolates and elucidate the potential overwintering of the virus in this Mediterranean region, complete genome sequencing, phylogenetic analyses, and a study of phenotypic characterisation were performed. Our results showed that these Spanish isolates belonged to the central-southern WNV-L2 clade. In more detail, they were related to the Lombardy cluster that emerged in Italy in 2013 and has been able to spread westwards, causing outbreaks in France (2018) and Spain (2017 and 2020). Phenotypic characterisation performed in vitro showed that these isolates presented characteristics corresponding to strains of moderate to high virulence. All these findings evidence that these WNV-L2 strains have been able to circulate and overwinter in the region, and are pathogenic, at least in northern goshawks, which seem to be very susceptible to WNV infection and may be good indicators of WNV-L2 circulation. Due to the increasing number of human and animal cases in Europe in the last years, this zoonotic flavivirus should be kept under extensive surveillance, following a One-Health approach.

Intensive West Nile Virus Circulation in Serbia in 2018-Results of Integrated Surveillance Program

The results of the Serbian national integrated West Nile virus (WNV) surveillance program conducted in 2018 and funded by the Serbian Veterinary Directorate are presented. The WNV surveillance program encompassed the entire territory of Serbia and was conducted by the veterinary service in collaboration with entomologists and ornithologists. The objective of the program was early detection of WNV circulation in the environment and timely reporting to the public health service and local authorities to increase clinical and mosquito control preparedness. The program was based on the detection of WNV presence in wild birds (natural hosts) and mosquitoes (virus vectors) and on serological testing of sentinel horses (WNV-specific IgM antibodies). The season 2018 was confirmed to be the season of the most intensive WNV circulation with the highest number and severity of human cases in Serbia ever reported. The most intense WNV circulation was observed in the northern and central parts of Serbia including Vojvodina Province, the Belgrade City area, and surrounding districts, where most positive samples were detected among sentinel animals, mosquitoes and wild birds. The majority of human cases were preceded by the detection of WNV circulation during the surveillance. The WNV surveillance program in 2018 showed satisfactory results in the capacity to indicate the spatial distribution of the risk for humans and sensitivity to early detection of WNV circulation in the environment.

Survey on the Presence of Viruses of Economic and Zoonotic Importance in Avifauna in Northern Italy

Wild birds play an important role in the circulation and spread of pathogens that are potentially zoonotic or of high economic impact on zootechnical production. They include, for example, West Nile virus (WNV), Usutu virus (USUV), avian influenza virus (AIV), and Newcastle disease virus (NDV), which, despite having mostly an asymptomatic course in wild birds, have a strong impact on public health and zootechnical production. This study investigated the presence of these viruses in several wild bird species from North Italy during the biennium 2019-2020. Wild birds derived from 76 different species belonging to 20 orders. Out of 679 birds, 27 were positive for WNV (lineage 2) with a prevalence of 4%; all birds were negative for USUV; one gull was positive for H13N6 influenza virus, and 12 samples were positive for NDV with a prevalence of 2%. Despite the low prevalence observed, the analyses performed on these species provide further data, allowing a better understanding of the diffusion and evolution of diseases of both economic and zoonotic importance.

Previous Usutu Virus Exposure Partially Protects Magpies (Pica pica) against West Nile Virus Disease But Does Not Prevent Horizontal Transmission

The mosquito-borne flaviviruses USUV and WNV are known to co-circulate in large parts of Europe. Both are a public health concern, and USUV has been the cause of epizootics in both wild and domestic birds, and neurological cases in humans in Europe. Here, we explore the susceptibility of magpies to experimental USUV infection, and how previous exposure to USUV would affect infection with WNV. None of the magpies exposed to USUV showed clinical signs, viremia, or detectable neutralizing antibodies. After challenge with a neurovirulent WNV strain, neither viremia, viral titer of WNV in vascular feathers, nor neutralizing antibody titers of previously USUV-exposed magpies differed significantly with respect to magpies that had not previously been exposed to USUV. However, 75% (6/8) of the USUV-exposed birds survived, while only 22.2% (2/9) of those not previously exposed to USUV survived. WNV antigen labeling by immunohistochemistry in tissues was less evident and more restricted in magpies exposed to USUV prior to challenge with WNV. Our data indicate that previous exposure to USUV partially protects magpies against a lethal challenge with WNV, while it does not prevent viremia and direct transmission, although the mechanism is unclear. These results are relevant for flavivirus ecology and contention.

Epidemiology of human West Nile virus infections in the European Union and European Union enlargement countries, 2010 to 2018

Background

West Nile virus (WNV) circulates in an enzootic cycle involving mosquitoes and birds; humans are accidental hosts.

Aim

We analysed human WNV infections reported between 2010 and 2018 to the European Centre for Disease Prevention and Control to better understand WNV epidemiology.

Methods

We describe probable and confirmed autochthonous human cases of WNV infection reported by European Union (EU) and EU enlargement countries. Cases with unknown clinical manifestation or with unknown place of infection at NUTS 3 or GAUL 1 level were excluded from analysis.

Results

From southern, eastern and western Europe, 3,849 WNV human infections and 379 deaths were reported. Most cases occurred between June and October. Two large outbreaks occurred, in 2010 (n = 391) and in 2018 (n = 1,993). The outbreak in 2018 was larger than in all previous years and the first cases were reported unusually early. The number of newly affected areas (n = 45) was higher in 2018 than in previous years suggesting wider spread of WNV.

Conclusion

Real-time surveillance of WNV infections is key to ensuring that clinicians and public health authorities receive early warning about the occurrence of cases and potential unusual seasonal patterns. Human cases may appear shortly after first detection of animal cases. Therefore, public health authorities should develop preparedness plans before the occurrence of human or animal WNV infections.

Akt Kinase Intervenes in Flavivirus Replication by Interacting with Viral Protein NS5

Arthropod-borne flaviviruses, such as Zika virus (ZIKV), Usutu virus (USUV), and West Nile virus (WNV), are a growing cause of human illness and death around the world. Presently, no licensed antivirals to control them are available and, therefore, search for broad-spectrum antivirals, including host-directed compounds, is essential. The PI3K/Akt pathway controls essential cellular functions involved in cell metabolism and proliferation. Moreover, Akt has been found to participate in modulating replication in different viruses including the flaviviruses. In this work we studied the interaction of flavivirus NS5 polymerases with the cellular kinase Akt. In vitro NS5 phosphorylation experiments with Akt showed that flavivirus NS5 polymerases are phosphorylated and co-immunoprecipitate by Akt. Polymerase activity assays of Ala- and Glu-generated mutants for the Akt-phosphorylated residues also indicate that Glu mutants of ZIKV and USUV NS5s present a reduced primer-extension activity that was not observed in WNV mutants. Furthermore, treatment with Akt inhibitors (MK-2206, honokiol and ipatasertib) reduced USUV and ZIKV titers in cell culture but, except for honokiol, not WNV. All these findings suggest an important role for Akt in flavivirus replication although with specific differences among viruses and encourage further investigations to examine the PI3K/Akt/mTOR pathway as an antiviral potential target.

West Nile virus in humans, Greece, 2018: the largest seasonal number of cases, 9 years after its emergence in the country

Background

Human cases of West Nile virus (WNV) infection are recorded since 2010 in Greece, with seasonal outbreaks occurring almost annually. Enhanced surveillance has been implemented since 2010, to promptly characterise cases’ temporal and geographical distribution and inform authorities for implementation of appropriate measures (mosquito control, health education, blood safety).

Aim

We describe the epidemiology of WNV human infections in Greece focusing on the 2018 season.

Methods

The National Public Health Organization advised physicians to test all suspect WNV infection cases and refer samples to reference laboratories. Laboratories notified diagnosed cases on a daily basis. Treating physicians, patients, and infected blood donors were interviewed within 48 hours after diagnosis and the probable infection location was identified. Hospitalised cases were followed up until discharge.

Results

A total of 317 autochthonous WNV infection cases were diagnosed in 2018. Among them, 243 cases had neuroinvasive disease (WNND), representing a 23% increase of WNND cases compared with 2010, the previous most intense season. There were 51 deaths. Cases started occurring from week 22, earlier than usual. Both rural and urban areas were affected, with 86 (26% of the total) municipalities belonging to seven (54% of the total) regions recording cases. Two major epicentres were identified in Attica and Central Macedonia regions.

Conclusions

The largest number of human cases of WNV infection ever recorded in Greece occurred in 2018, with a wide geographical distribution, suggesting intense virus circulation. Enhanced surveillance is vital for the early detection of human cases and the prompt implementation of response measures.

The Role of Birds of Prey in West Nile Virus Epidemiology

Reported human cases of West Nile virus (WNV) in Europe increased dramatically in 2018. Lineage 1 strains had been circulating in Euro-Mediterranean countries since the early 1990s. The subsequent introduction of WNV lineage 2 has been responsible for the remarkable upsurge of European WNV outbreaks since 2004, including the dramatic increase in human cases observed since 2018. The virus exists in a natural cycle between mosquitoes and wild birds, with humans and horses acting as dead-end hosts. As the key vertebrate hosts in the transmission cycle of WNV, avian species have been the focus of surveillance across many countries. Raptors appear particularly susceptible to WNV infection, resulting in higher prevalence, and in some cases exhibiting neurological signs that lead to the death of the animal. In addition, birds of prey are known to play an important role as WNV reservoir and potentially amplifying hosts of infection. Importantly, raptor higher susceptibility/prevalence may indicate infection through predation of infected prey. Consequently, they are considered important target species when designing cost-effective surveillance for monitoring both seasonal WNV circulation in endemic countries and its emergence into new areas, where migrating raptors may play a critical role in virus introduction. This review summarizes the different aspects of the current knowledge of WNV infection in birds of prey and evaluates their role in the evolution of the epizootic that is spreading throughout Europe.

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.

Epidemiology of Usutu Virus: The European Scenario

Usutu virus (USUV) is an emerging arbovirus isolated in 1959 (Usutu River, Swaziland). Previously restricted to sub-Saharan Africa, the virus was introduced in Europe in 1996. While the USUV has received little attention in Africa, the virus emergence has prompted numerous studies with robust epidemiological surveillance programs in Europe. The natural transmission cycle of USUV involves mosquitoes (vectors) and birds (amplifying hosts) with humans and other mammals considered incidental ("dead-end") hosts. In Africa, the virus was isolated in mosquitoes, rodents and birds and serologically detected in horses and dogs. In Europe, USUV was detected in bats, whereas antibodies were found in different animal species (horses, dogs, squirrels, wild boar, deer and lizards). While bird mortalities were not reported in Africa, in Europe USUV was shown to be highly pathogenic for several bird species, especially blackbirds (Turdus merula) and great gray owls (Strix nebulosa). Furthermore, neurotropism of USUV for humans was reported for the first time in both immunocompromised and immunocompetent patients. Epizootics and genetic diversity of USUV in different bird species as well as detection of the virus in mosquitoes suggest repeated USUV introductions into Europe with endemization in some countries. The zoonotic potential of USUV has been reported in a growing number of human cases. Clinical cases of neuroinvasive disease and USUV fever, as well as seroconversion in blood donors were reported in Europe since 2009. While most USUV strains detected in humans, birds and mosquitoes belong to European USUV lineages, several reports indicate the presence of African lineages as well. Since spreading trends of USUV are likely to continue, continuous multidisciplinary interventions ("One Health" concept) should be conducted for monitoring and prevention of this emerging arboviral infection.

Clinical, pathological and virological aspects of fatal West Nile virus infections in ten free-ranging goshawks (Accipiter gentilis) in Germany

West Nile virus (WNV), a zoonotic arbovirus, is a new epizootic disease in Germany and caused increasing avian and equine mortality since its first detection in 2018. The northern goshawk (Accipiter gentilis) is highly susceptible to fatal WNV disease and thus is considered as an indicator species for WNV emergence in European countries. Therefore, information regarding clinical presentation and pathological findings is important for identifying suspect cases and initiating further virological diagnostics. Between July and September 2019, ten free-ranging goshawks were admitted to the Small Animal Clinic of the Freie Universität Berlin with later confirmed WNV infection. Clinical, pathological and virological findings are summarized in this report. All birds were presented obtunded and in poor to cachectic body condition. Most of the birds were juveniles (8/10) and females (9/10). Neurologic abnormalities were observed in all birds and included stupor (3/10), seizures (3/10), head tremor (2/10), head tilt (2/10), ataxia (2/10) and monoplegia (2/10). Concurrent diseases like aerosacculitis/pneumonia (7/10), clinical infections with Eucoleus spp. and Trichomonas spp. (3/10), trauma-related injuries (3/10) and myiasis (2/10) were found. Blood analysis results were unspecific considering concurrent diseases. Median time of survival was two days. The most common pathological findings were meningoencephalitis (9/10), myocarditis (8/10), iridocyclitis (8/8) and myositis (7/10). WNV infection was diagnosed by real-time quantitative reverse transcription polymerase chain reaction and confirmed by serology and immunohistochemistry.

Detection of enzootic circulation of a new strain of West Nile virus lineage 1 in sentinel chickens in the north of Tunisia

Tunisia has experienced various West Nile disease outbreaks. Notwithstanding the serological and molecular confirmations in humans, horses and birds, the human surveillance system can still be improved. Three sentinel chicken flocks were placed in different Tunisian endemic regions and followed up from September 2016 to January 2017. A total of 422 sera from Sejnene (north of Tunisia), 392 from Moknine (east coast of Tunisia) and 386 from Tozeur (south of Tunisia) were tested for West Nile-specific antibodies and viral RNA. The WNV elisa positive rate in sentinel chickens in Sejnene was 10.7% (95% CI: 5.08-21.52). No positive samples were detected in Moknine. In Tozeur, the overall serological elisa positive rate during the study period was 9.8% (95% CI:4.35-21.03). West Nile virus nucleic acid was detected in two chickens in Sejnene.Phylogenetic analysis of one of the detected partial NS3 gene sequences showed that recent Tunisian WNV strain belong to WNV lineage 1 and is closely related to Italian strains detected in mosquitoes in 2016 and in a sparrow hawk in 2017. This report showed the circulation, first molecular detection and sequencing of WNV lineage 1 in chickens in the north of Tunisia and highlights the use of poultry as a surveillance tool to detect WNV transmission in a peri-domestic area.

Assessment of climate change impact on the malaria vector Anopheles hyrcanus, West Nile disease, and incidence of melanoma in the Vojvodina Province (Serbia) using data from a regional climate model

Motivated by the One Health paradigm, we found the expected changes in temperature and UV radiation (UVR) to be a common trigger for enhancing the risk that viruses, vectors, and diseases pose to human and animal health. We compared data from the mosquito field collections and medical studies with regional climate model projections to examine the impact of climate change on the spreading of one malaria vector, the circulation of West Nile virus (WNV), and the incidence of melanoma. We analysed data obtained from ten selected years of standardised mosquito vector sampling with 219 unique location-year combinations, and 10 years of melanoma incidence. Trends in the observed data were compared to the climatic variables obtained by the coupled regional Eta Belgrade University and Princeton Ocean Model for the period 1961-2015 using the A1B scenario, and the expected changes up to 2030 were presented. Spreading and relative abundance of Anopheles hyrcanus was positively correlated with the trend of the mean annual temperature. We anticipated a nearly twofold increase in the number of invaded sites up to 2030. The frequency of WNV detections in Culex pipiens was significantly correlated to overwintering temperature averages and seasonal relative humidity at the sampling sites. Regression model projects a twofold increase in the incidence of WNV positive Cx. pipiens for a rise of 0.5°C in overwintering TOctober-April temperatures. The projected increase of 56% in the number of days with Tmax ≥ 30°C (Hot Days-HD) and UVR doses (up to 1.2%) corresponds to an increasing trend in melanoma incidence. Simulations of the Pannonian countries climate anticipate warmer and drier conditions with possible dominance of temperature and number of HD over other ecological factors. These signal the importance of monitoring the changes to the preparedness of mitigating the risk of vector-borne diseases and melanoma.

Emerging Trends in the Epidemiology of West Nile and Usutu Virus Infections in Southern Europe

The epidemiology of West Nile (WNV) and Usutu virus (USUV) has changed dramatically over the past two decades. Since 1999, there have been regular reports of WNV outbreaks and the virus has expanded its area of circulation in many Southern European countries. After emerging in Italy in 1996, USUV has spread to other countries causing mortality in several bird species. In 2009, USUV seroconversion in horses was reported in Italy. Co-circulation of both viruses was detected in humans, horses and birds. The main vector of WNV and USUV in Europe is Culex pipiens, however, both viruses were found in native Culex mosquito species (Cx. modestus, Cx. perexiguus). Experimental competence to transmit the WNV was also proven for native and invasive mosquitoes of Aedes and Culex genera (Ae. albopictus, Ae. detritus, Cx. torrentium). Recently, Ae. albopictus and Ae. japonicus naturally-infected with USUV were reported. While neuroinvasive human WNV infections are well-documented, USUV infections are sporadically detected. However, there is increasing evidence of a role of USUV in human disease. Seroepidemiological studies showed that USUV circulation is more common than WNV in some endemic regions. Recent data showed that WNV strains detected in humans, horses, birds, and mosquitoes mainly belong to lineage 2. In addition to European USUV lineages, some reports indicate the presence of African USUV lineages as well. The trends in WNV/USUV range and vector expansion are likely to continue in future years. This mini-review provides an update on the epidemiology of WNV and USUV infections in Southern Europe within a multidisciplinary "One Health" context.

Current Progress of Avian Vaccines Against West Nile Virus

Birds are the main natural host of West Nile virus (WNV), the worldwide most distributed mosquito-borne flavivirus, but humans and equids can also be sporadic hosts. Many avian species have been reported as susceptible to WNV, particularly corvids. In the case that clinical disease develops in birds, this is due to virus invasion of different organs: liver, spleen, kidney, heart, and mainly the central nervous system, which can lead to death 24–48 h later. Nowadays, vaccines have only been licensed for use in equids; thus, the availability of avian vaccines would benefit bird populations, both domestic and wild ones. Such vaccines could be used in endangered species housed in rehabilitation and wildlife reserves, and in animals located at zoos and other recreational installations, but also in farm birds, and in those that are grown for hunting and restocking activities. Even more, controlling WNV infection in birds can also be useful to prevent its spread and limit outbreaks. So far, different commercial and experimental vaccines (inactivated, attenuated, and recombinant viruses, and subunits and DNA-based candidates) have been evaluated, with various regimens, both in domestic and wild avian species. However, there are still disadvantages that must be overcome before avian vaccination can be implemented, such as its cost-effectiveness for domestic birds since in many species the pathogenicity is low or zero, or the viability of being able to achieve collective immunity in wild birds in freedom. Here, a comprehensive review of what has been done until now in the field of avian vaccines against WNV is presented and discussed.

Evidence of West Nile Virus (WNV) Circulation in Wild Birds and WNV RNA Negativity in Mosquitoes of the Danube Delta Biosphere Reserve, Romania, 2016

West Nile virus (WNV) is a zoonotic flavivirus whose transmission cycle in nature includes wild birds as amplifying hosts and ornithophilic mosquito vectors. Bridge vectors can transmit WNV to mammal species potentially causing West Nile Fever. Wild bird migration is a mode of WNV introduction into new areas. The Danube Delta Biosphere Reserve (DDBR) is a major stopover of wild birds migrating between Europe and Africa. The aim of this study was to investigate the presence of WNV in the DDBR during the 2016 transmission season in wild birds and mosquitoes. Blood from 68 wild birds (nine different species) trapped at four different locations was analyzed by competitive ELISA and Virus Neutralization Test (VNT), revealing positive results in 8/68 (11.8%) of the wild birds by ELISA of which six samples (three from juvenile birds) were confirmed seropositive by VNT. Mosquitoes (n = 6523, 5 genera) were trapped with CDC Mini Light traps at two locations and in one location resting mosquitoes were caught. The presence of WNV RNA was tested in 134 pools by reverse transcription quantitative PCR (RT-qPCR). None of the pools was positive for WNV-specific RNA. Based on the obtained results, WNV was circulating in the DDBR during 2016.

A Recombinant Subviral Particle-Based Vaccine Protects Magpie (Pica pica) Against West Nile Virus Infection

The mosquito-borne West Nile virus (WNV) is a highly neurovirulent Flavivirus currently representing an emergent zoonotic concern. WNV cycles in nature between mosquito vectors and birds that act as amplifier hosts and play an essential role in virus ecology, being, thus, WNV a threat to many species. Availability of an efficient avian vaccine would benefit certain avian populations, both birds grown for hunting and restocking activities, as well as endangered species in captive breeding projects, wildlife reservations, and recreation installations, and would be useful to prevent and contain outbreaks. Avian vaccination would be also of interest to limit WNV spillover to humans or horses from susceptible bird species that live in urbanized landscapes, like magpies. Herein, we have addressed the efficacy of a single dose of a WNV recombinant subviral particle (RSP) vaccine in susceptible magpie (Pica pica). The protective capacity of the RSP-based vaccine was demonstrated upon challenge of magpies with 5 × 10³ plaque forming units of a neurovirulent WNV strain. A significant improvement in survival rates of immunized birds was recorded when compared to vehicle-inoculated animals (71.4 vs. 22.2%, respectively). Viremia, which is directly related to the capacity of a host to be competent for virus transmission, was reduced in vaccinated animals, as was the presence of infectious virus in feather follicles. Bird-to-bird transmission was recorded in three of six unchallenged (contact) magpies housed with non-vaccinated WNV-infected birds, but not in contact animals housed with vaccinated WNV-infected magpies. These results demonstrate the protective efficacy of the RSP-based vaccine in susceptible birds against WNV infection and its value in controlling the spread of the virus.

Evidence of the first clinical case of equine neuroinvasive West Nile disease in Serbia, 2018

During July 2018, the first clinical case of neurological West Nile virus (WNV) infection was reported in a Belgian sports mare in Belgrade, Serbia. Typical symptoms, such as hypersensitive skin reaction, disorientation, weakness, ataxia and the loss of equilibrium were reported. Detection of WNV IgM antibodies by commercial ELISA in the serum samples of the diseased mare strongly indicated acute infection. The ELISA positive results were confirmed by VNT. Hematological and biochemical parameters were in the reference range. The only finding was a minor lymphopenia. WNV RNA was not detected by RT-qPCR in the blood sample extracted seven days after the disease had broken out. The horse improved clinically in two weeks while other horses at the same premises remained asymptomatic. The clinical, serological, biochemical and molecular analyses applied confirmed the first clinical case of neuroinvasive WNV infection in horses in Serbia. The West Nile virus has been circulating in Serbia in the last decade in mosquitoes, birds, and horses, but no evidence of equine WNV clinical cases were registered so far.

Mortality of Goshawks (Accipiter gentilis) Due to West Nile Virus Lineage 2

In 2017, we isolated and identified West Nile virus (WNV) lineage 2 from two dead captive goshawks (Accipiter gentilis), for the first time in the Czech Republic. Goshawk might serve as an early indicator species for the ongoing WNV emergence in several European countries.

West Nile virus and other mosquito-borne viruses present in Eastern Europe

Eastern Europe (EE) has been severely affected by mosquito-borne viruses (moboviruses). In this review, we summarize the epidemiology of moboviruses, with particular attention to West Nile virus (WNV). The study of WNV human cases in EE between 2010 and 2016, revealed that the epidemiology of WNV in EE is complex with the combination of introduction of different WNV strains from lineages 1 and 2, and the establishment of endemic cycles. We found a positive correlation between the risk of WNV re-emergence in an area and the number of human cases reported in the previous year. We also report the main ecological and biological characteristics of the key mosquito species vectors of moboviruses. Recent expansion of invasive mosquito species in EE, mainly Aedes albopictus but also Aedes aegypti and Culex quinquefasciatus, may result in new scenarios with an increased risk of transmission of moboviruses. Main gaps of knowledge in relation to moboviruses and their vectors in EE are identified. Understanding the epidemiology of moboviruses in EE is essential for the improvement of their surveillance and the control of the diseases they cause.

Susceptibility and role as competent host of the red-legged partridge after infection with lineage 1 and 2 West Nile virus isolates of Mediterranean and Central European origin

West Nile virus (WNV; genus Flavivirus; family Flaviviridae) is the aetiological agent of an emerging, mosquito-borne disease with great impact on human and animal health. Over the past 15 years, WNV has been responsible for large epidemics mainly in North America but also in Europe, where lineage 1 and more recently lineage 2 strains have caused an upsurge in the number of outbreaks with increased human infection and higher virulence for certain wild bird species. This study aimed to compare the course of infection of the lineage 1 WNV strains Israel/98 and Italy/08 and the lineage 2 strain Austria/08 in the red-legged partridge (Alectoris rufa), a gallinaceous bird indigenous to the Iberian Peninsula and widely distributed in Southern and Western Europe. After experimental inoculation, clinical and analytic parameters (viraemia, viral load, antibodies) were examined over a period of 15 days. All inoculated birds became viremic and showed clinical disease, with a morbidity rate of 100% and mortality rates between 22.2 and 55.5% depending on the virus strain. The red-legged partridge demonstrated to be a competent host for transmission of the three investigated WNV isolates with the highest competence index observed for the Italian strain. Likewise, this strain was the most pathogenic causing the highest viral loads in blood, organs, feathers and oral and cloacal secretions. These experimental results indicate that the red-legged partridge is highly susceptible to the infection with lineage 1 and 2 WNV strains and that this species may act as an amplifying host for both WNV lineages.

High susceptibility of magpie (Pica pica) to experimental infection with lineage 1 and 2 West Nile virus

West Nile virus (WNV), a zoonotic pathogen naturally transmitted by mosquitoes whose natural hosts are birds, has spread worldwide during the last few decades. Resident birds play an important role in flavivirus epidemiology, since they can serve as reservoirs and facilitate overwintering of the virus. Herein, we report the first experimental infection of magpie (Pica pica) with two strains of West Nile virus, lineages 1 (NY-99) and 2 (SRB Novi-Sad/12), which are currently circulating in Europe. Magpies were highly susceptible to WNV infection, with similar low survival rates (30% and 42.8%) for both lineages. All infected magpies developed viremia detectable at 3 days post-infection with titers above those necessary for successful transmission of WNV to a mosquito. Neutralizing antibodies were detected at all time points analyzed (from 7 to 17 days post-infection). WNV genome was detected in the brains and hearts of all magpies that succumbed to the infection, and, in some of the surviving birds. WNV-RNA was amplified from swabs (oral and cloacal) at 3, 6 and 7 days post-infection and feather pulps, from 3 to 17 days post-infection, of infected animals. Even more, infectious virus was recovered from swabs up to 7 days post-infection and from feather pulps up to 10 days post infection. Sham-infected control animals were negative for viremia, viral RNA, and antibodies. These results suggest that the magpie, which is one of the most abundant corvid species in Europe, could represent a source of WNV transmission for birds and humans. Our observations shed light on the pathogenesis, transmission, and ecology of WNV and can benefit the implementation of surveillance and control programs.

Birds play an important role in the epidemiology of flaviviruses such as West Nile virus (WNV) since birds are natural hosts and facilitate hibernation of the virus in periods of absence of mosquitoes that transmit the virus. Since it has been proposed that magpies play an important role in an endemic WNV cycle in human habitats in Europe, we conducted the first experimental infection of magpie with the two WNV lineages currently circulating in Europe. We observed high susceptibility of magpie to WNV infection with virus titers higher than those necessary for the successful transmission of WNV to a mosquito and often resulting in death. Likewise, we detected elevated titers of neutralizing antibodies in all the samples tested as well as the viral genome in the organs, oropharyngeal and cloacal swabs and feather pulps of the infected animals. Our results suggest that the magpie, which is one of the most abundant corvid species in Europe, could be a source of WNV transmission to other birds and humans, which expands the knowledge about WNV pathogenesis, transmission and ecology, that benefits monitoring and control programs.

Methodology and results of integrated WNV surveillance programmes in Serbia

Studies conducted during the past few years have confirmed active West Nile virus (WNV) circulation in Serbia. Based on these studies and the epidemiological situation, the Veterinary Directorate of the Ministry of Agriculture and Environmental Protection launched national WNV surveillance programmes in 2014 and 2015. The programmes encompassed the territory of Serbia and were conducted by the veterinary service in collaboration with entomologists and ornithologists. The objective of the programmes was early detection of WNV and timely reporting to the public health service and local authorities to increase both clinical and mosquito control preparedness. The WNV surveillance programmes were based on direct and indirect surveillance of the presence of WNV by the serological testing of initially seronegative sentinel horses and chickens as well as through viral detection in pooled mosquito and wild bird samples. The most intense WNV circulation was observed in all seven districts of Vojvodina Province (northern Serbia) and Belgrade City, where most of the positive samples were detected among sentinel animals, mosquitoes and wild birds. The West Nile virus surveillance programmes in 2014 and 2015 showed satisfactory results in their capacity to indicate the spatial distribution of the risk for humans and their sensitivity to early detect viral circulation at the enzootic level. Most of the human cases were preceded by the detection of WNV circulation as part of the surveillance programmes. According to the existing data, it can be reasonably assumed that WNV infection, now an endemic infection in Serbia, will continue to present a significant problem for the veterinary service and public health.

Integrated analysis of human-animal-vector surveillance: West Nile virus infections in Austria, 2015-2016

The results of integrated human and veterinary surveillance for West Nile virus (WNV) infections in Austria during the transmission seasons 2015 and 2016 are shown. Altogether WNV nucleic acid was detected in 21 humans, horses, wild birds and mosquito pools. In detail: in four human clinical cases [two cases of West Nile fever (WNF) and two cases of West Nile neuroinvasive disease (WNND)]; eight blood donors [among 145,541 tested donations], of which three remained asymptomatic and five subsequently developed mild WNF; two horses with WNND, of which one recovered and one had to be euthanized; two wild birds [one goshawk and one falcon, both succumbed to WNND]; and five Culex pipiens mosquito pools. Compared to previous years the number of infections increased remarkably. All infections were recorded in the city of Vienna and neighboring regions of Lower Austria. Sixteen coding-complete WNV sequences were established which were closely related to each other and to other Austrian, Czech and Italian viruses, all belonging to the Central/Southern European cluster of WNV sublineage 2d. However, several genetically slightly different WNV strains seem to co-circulate in the same area, as demonstrated by phylogenetic analysis. Based on detailed sequence analysis, all newly discovered Austrian WNV strains had the potential to cause neurological disease, but no correlation was found between severity of disease and the analyzed genetic virulence/neuroinvasiveness markers. Results of integrated human-animal-vector surveillance presented in this paper provide a comprehensive description of WNV activity in the region and will facilitate proactive public health measures to prevent or mitigate potential outbreaks.

A Survey on West Nile and Usutu Viruses in Horses and Birds in Poland

West Nile virus (WNV) and Usutu virus (USUV) are members of the family Flaviviridae which, natural life cycles involve mosquito–bird–mosquito transmission. Both represent emerging viruses in Europe with potential to cause neuroinvasive disease in humans. This study investigates the seroprevalence of serum neutralizing antibodies to WNV and to USUV in birds and in horses in Poland. Antibodies against WNV and USUV were detected in 5 (35.7%) and in 1 (7.14%) of 14 birds and in 62 (15.08%) and in 115 (27.98%) of 411 horses, respectively. Twenty-one WNV serologically positive horses (33.87%) and 67 USUV serologically positive horses (58.26%) did not travel outside Polish borders. Given the high abundance of potentially competent mosquito species in Poland, high populations of horses and different bird species, our findings highlight implementation of active control programs, including monitoring of geographic spread and dynamics of WNV and USUV transmission in both primary and accidental hosts. It is also important to improve public health awareness about the disease these viruses may cause.

West Nile Virus Lineage 2 Associated with Human Case in Republic of Serbia

A suspicion on West Nile virus (WNV) in Serbia was first reported in 1972 by a seroprevalence study, after which no data were available for four decades. We report full sequence of the isolate obtained for the first time from a human sample in Serbia. The closest clustering was obtained with lineage 2 WNV identified in Greece in 2010. Since WNV lineage 2 emerged in Europe in 2004, a cocirculation of lineages 1 and 2-as observed in Hungary and Italy-cannot be excluded. The reinforcement of surveillance will be required to investigate the possible cocirculation of the two lineages and the burden of WNV in the local population.

Geographic variations of the bird-borne structural risk of West Nile virus circulation in Europe

The structural risk of West Nile Disease results from the usual functioning of the socio-ecological system, which may favour the introduction of the pathogen, its circulation and the occurrence of disease cases. Its geographic variations result from the local interactions between three components: (i) reservoir hosts, (ii) vectors, both characterized by their diversity, abundance and competence, (iii) and the socio-economic context that impacts the exposure of human to infectious bites. We developed a model of bird-borne structural risk of West Nile Virus (WNV) circulation in Europe, and analysed the association between the geographic variations of this risk and the occurrence of WND human cases between 2002 and 2014. A meta-analysis of WNV serosurveys conducted in wild bird populations was performed to elaborate a model of WNV seropositivity in European bird species, considered a proxy for bird exposure to WNV. Several eco-ethological traits of bird species were linked to seropositivity and the statistical model adequately fitted species-specific seropositivity data (area under the ROC curve: 0.85). Combined with species distribution maps, this model allowed deriving geographic variations of the bird-borne structural risk of WNV circulation. The association between this risk, and the occurrence of WND human cases across the European Union was assessed. Geographic risk variations of bird-borne structural risk allowed predicting WND case occurrence in administrative districts of the EU with a sensitivity of 86% (95% CI: 0.79-0.92), and a specificity of 68% (95% CI: 0.66-0.71). Disentangling structural and conjectural health risks is important for public health managers as risk mitigation procedures differ according to risk type. The results obtained show promise for the prevention of WND in Europe. Combined with analyses of vector-borne structural risk, they should allow designing efficient and targeted prevention measures.

Zika virus infection confers protection against West Nile virus challenge in mice

Flaviviruses are RNA viruses that constitute a worrisome threat to global human and animal health. Zika virus (ZIKV), which was initially reported to cause a mild disease, recently spread in the Americas, infecting millions of people. During this recent epidemic, ZIKV infection has been linked to serious neurological diseases and birth defects, specifically Guillain-Barrè syndrome (GBS) and microcephaly. Because information about ZIKV immunity remains scarce, we assessed the humoral response of immunocompetent mice to infection with three viral strains of diverse geographical origin (Africa, Asia and America). No infected animals showed any sign of disease or died after infection. However, specific neutralizing antibodies were elicited in all infected mice. Considering the rapid expansion of ZIKV throughout the American continent and its co-circulation with other medically relevant flaviviruses, such as West Nile virus (WNV), the induction of protective immunity between ZIKV and WNV was analyzed. Remarkably, protection after challenge with WNV was observed in mice previously infected with ZIKV, as survival rates were significantly higher than in control mice. Moreover, previous ZIKV infection enhanced the humoral immune response against WNV. These findings may be relevant in geographical areas where both ZIKV and WNV co-circulate, as well as for the future development of broad-spectrum flavivirus vaccines.

Antiviral Activity of Nordihydroguaiaretic Acid and Its Derivative Tetra-O-Methyl Nordihydroguaiaretic Acid against West Nile Virus and Zika Virus

Flaviviruses are positive-strand RNA viruses distributed all over the world that infect millions of people every year and for which no specific antiviral agents have been approved. These viruses include the mosquito-borne West Nile virus (WNV), which is responsible for outbreaks of meningitis and encephalitis. Considering that nordihydroguaiaretic acid (NDGA) has been previously shown to inhibit the multiplication of the related dengue virus and hepatitis C virus, we have evaluated the effect of NDGA, and its methylated derivative tetra-O-methyl nordihydroguaiaretic acid (M₄N), on the infection of WNV. Both compounds inhibited the infection of WNV, likely by impairing viral replication. Since flavivirus multiplication is highly dependent on host cell lipid metabolism, the antiviral effect of NDGA has been previously related to its ability to disturb the lipid metabolism, probably by interfering with the sterol regulatory element-binding proteins (SREBP) pathway. Remarkably, we observed that other structurally unrelated inhibitors of the SREBP pathway, such as PF-429242 and fatostatin, also reduced WNV multiplication, supporting that the SREBP pathway may constitute a druggable target suitable for antiviral intervention against flavivirus infection. Moreover, treatment with NDGA, M₄N, PF-429242, and fatostatin also inhibited the multiplication of the mosquito-borne flavivirus Zika virus (ZIKV), which has been recently associated with birth defects (microcephaly) and neurological disorders. Our results point to SREBP inhibitors, such as NDGA and M₄N, as potential candidates for further antiviral development against medically relevant flaviviruses.

Potential disease transmission from wild geese and swans to livestock, poultry and humans: a review of the scientific literature from a One Health perspective

There are more herbivorous waterfowl (swans and geese) close to humans, livestock and poultry than ever before. This creates widespread conflict with agriculture and other human interests, but also debate about the role of swans and geese as potential vectors of disease of relevance for human and animal health. Using a One Health perspective, we provide the first comprehensive review of the scientific literature about the most relevant viral, bacterial, and unicellular pathogens occurring in wild geese and swans. Research thus far suggests that these birds may play a role in transmission of avian influenza virus, Salmonella, Campylobacter, and antibiotic resistance. On the other hand, at present there is no evidence that geese and swans play a role in transmission of Newcastle disease, duck plague, West Nile virus, Vibrio, Yersinia, Clostridium, Chlamydophila, and Borrelia. Finally, based on present knowledge it is not possible to say if geese and swans play a role in transmission of Escherichia coli, Pasteurella, Helicobacter, Brachyspira, Cryptosporidium, Giardia, and Microsporidia. This is largely due to changes in classification and taxonomy, rapid development of identification methods and lack of knowledge about host specificity. Previous research tends to overrate the role of geese and swans as disease vectors; we do not find any evidence that they are significant transmitters to humans or livestock of any of the pathogens considered in this review. Nevertheless, it is wise to keep poultry and livestock separated from small volume waters used by many wild waterfowl, but there is no need to discourage livestock grazing in nature reserves or pastures where geese and swans are present. Under some circumstances it is warranted to discourage swans and geese from using wastewater ponds, drinking water reservoirs, and public beaches. Intensified screening of swans and geese for AIV, West Nile virus and anatid herpesvirus is warranted.

Surveillance of Arthropod-Borne Viruses and Their Vectors in the Mediterranean and Black Sea Regions Within the MediLabSecure Network

PURPOSE OF REVIEW

Arboviruses, viruses transmitted by arthropods such as mosquitoes, ticks, sandflies, and fleas are a significant threat to public health because of their epidemic and zoonotic potential. The geographical distribution of mosquito-borne diseases such as West Nile (WN), Rift Valley fever (RVF), Dengue, Chikungunya, and Zika has expanded over the last decades. Countries of the Mediterranean and Black Sea regions are not spared. Outbreaks of WN are repeatedly reported in the Mediterranean basin. Human cases of RVF were reported at the southern borders of the Maghreb region. For this reason, establishing the basis for the research to understand the potential for the future emergence of these and other arboviruses and their expansion into new geographic areas became a public health priority. In this context, the European network "MediLabSecure" gathering laboratories in 19 non-EU countries from the Mediterranean and Black Sea regions seeks to improve the surveillance (of animals, humans, and vectors) by reinforcing capacity building and harmonizing national surveillance systems to address this important human and veterinary health issue. The aim of this review is to give an exhaustive overview of arboviruses and their vectors in the region.

RECENT FINDINGS

The data presented underline the importance of surveillance in the implementation of more adapted control strategies to combat vector-borne diseases. Partner laboratories within the MediLabSecure network present a wide range of infrastructures and have benefited from different training programs.

SUMMARY

Although reporting of arboviral presence is not carried out in a systematic manner, the expansion of the area where arboviruses are present cannot be disputed. This reinforces the need for increasing surveillance capacity building in this region to prevent future emergences.

West Nile virus 'circulation' in Vojvodina, Serbia: Mosquito, bird, horse and human surveillance

Efforts to detect West Nile virus (WNV) in the Vojvodina province, northern Serbia, commenced with human and mosquito surveillance in 2005, followed by horse (2009) and wild bird (2012) surveillance. The knowledge obtained regarding WNV circulation, combined with the need for timely detection of virus activity and risk assessment resulted in the implementation of a national surveillance programme integrating mosquito, horse and bird surveillance in 2014. From 2013, the system showed highly satisfactory results in terms of area specificity (the capacity to indicate the spatial distribution of the risk for human cases of West Nile neuroinvasive disease - WNND) and sensitivity to detect virus circulation even at the enzootic level. A small number (n = 50) of Culex pipiens (pipiens and molestus biotypes, and their hybrids) females analysed per trap/night, combined with a high number of specimens in the sample, provided variable results in the early detection capacity at different administrative levels (NUTS2 versus NUTS3). The clustering of infected mosquitoes, horses, birds and human cases of WNND in 2014-2015 was highly significant, following the south-west to north-east direction in Vojvodina (NUTS2 administrative level). Human WNND cases grouped closest with infected mosquitoes in 2014, and with wild birds/mosquitoes in 2015. In 2014, sentinel horses showed better spatial correspondence with human WNND cases than sentinel chickens. Strong correlations were observed between the vector index values and the incidence of human WNND cases recorded at the NUTS2 and NUTS3 levels. From 2010, West Nile virus was detected in mosquitoes sampled at 43 different trap stations across Vojvodina. At 14 stations (32.56%), WNV was detected in two different (consecutive or alternate) years, at 2 stations in 3 different years, and in 1 station during 5 different years. Based on these results, integrated surveillance will be progressively improved to allow evidence-based adoption of preventive public health and mosquito control measures.

Ecology of West Nile virus across four European countries: review of weather profiles, vector population dynamics and vector control response

West Nile virus (WNV) represents a serious burden to human and animal health because of its capacity to cause unforeseen and large epidemics. Until 2004, only lineage 1 and 3 WNV strains had been found in Europe. Lineage 2 strains were initially isolated in 2004 (Hungary) and in 2008 (Austria) and for the first time caused a major WNV epidemic in 2010 in Greece with 262 clinical human cases and 35 fatalities. Since then, WNV lineage 2 outbreaks have been reported in several European countries including Italy, Serbia and Greece. Understanding the interaction of ecological factors that affect WNV transmission is crucial for preventing or decreasing the impact of future epidemics. The synchronous co-occurrence of competent mosquito vectors, virus, bird reservoir hosts, and susceptible humans is necessary for the initiation and propagation of an epidemic. Weather is the key abiotic factor influencing the life-cycles of the mosquito vector, the virus, the reservoir hosts and the interactions between them. The purpose of this paper is to review and compare mosquito population dynamics, and weather conditions, in three ecologically different contexts (urban/semi-urban, rural/agricultural, natural) across four European countries (Italy, France, Serbia, Greece) with a history of WNV outbreaks. Local control strategies will be described as well. Improving our understanding of WNV ecology is a prerequisite step for appraising and optimizing vector control strategies in Europe with the ultimate goal to minimize the probability of WNV infection.

High Prevalence of West Nile Virus in Domestic Birds and Detection in 2 New Mosquito Species in Madagascar

West Nile virus is an arthropod-borne zoonosis transmitted by a large number of mosquito species, and birds play a key role as reservoir of the virus. Its distribution is largely widespread over Africa, Asia, the Americas and Europe. Since 1978, it has frequently been reported in Madagascar. Studies described a high seroprevalence level of the virus in humans in different areas of the island and a human fatal case of WNV infection was reported in 2011. Despite these reports, the epidemiology of WNV in Madagascar, in particular, viral circulation remains unclear. To explore the transmission of WNV in two rural human populations of Madagascar, we investigated local mosquitoes and poultry for evidence of current infections, and determined seroprevalence of candidate sentinel species among the local poultry. These 2 areas are close to lakes where domestic birds, migratory wild birds and humans coexist. Serological analysis revealed WNV antibodies in domestic birds (duck, chicken, goose, turkey and guinea fowl) sampled in both districts (Antsalova 29.4% and Mitsinjo 16.7%). West Nile virus nucleic acid was detected in one chicken and in 8 pools of mosquitoes including 2 mosquito species (Aedeomyia madagascarica and Anopheles pauliani) that have not been previously described as candidate vectors for WNV. Molecular analysis of WNV isolates showed that all viruses detected were part of the lineage 2 that is mainly distributed in Africa, and were most closely matched by the previous Malagasy strains isolated in 1988. Our study showed that WNV circulates in Madagascar amongst domestic birds and mosquitoes, and highlights the utility of poultry as a surveillance tool to detect WNV transmission in a peri-domestic setting.

Evaluation of the pathogenicity of West Nile virus (WNV) lineage 2 strains in a SPF chicken model of infection: NS3-249Pro mutation is neither sufficient nor necessary for conferring virulence

Lineage 2 West Nile virus (WNV) strains were reported for the first time in Europe in 2004. Despite an almost silent circulation around their entry point in Hungary, an upsurge of pathogenicity occurred in 2010 as 262 people suffered from neuroinvasive disease in Greece. This increase in virulence was imputed to the emergence of a His249Pro mutation in the viral NS3 helicase, as previously evidenced in American crows experimentally infected with the prototype lineage 1 North-American WNV strain. However, since 2003, WNV strains bearing the NS3Pro genotype are regularly isolated in Western-Mediterranean countries without being correlated to any virulent outbreak in vertebrates. We thus sought to evaluate the weight of the NS3_249Pro genotype as a virulence marker of WNV in an in vivo avian model of WNV infection. We therefore characterized three genetically-related Eastern-Europe lineage 2 WNV strains in day-old specific pathogen-free (SPF) chickens: Hun2004 and Aus2008 which are both characterized by a NS3_249His genotype, and Gr2011 which is characterized by a NS3_249Pro genotype. Unlike Hun2004 and Aus2008, Gr2011 was weakly virulent in SPF chicks as Gr2011-induced viremia was lower and waned quicklier than in the Hun2004 and Aus2008 groups. Overall, this study showed that the presence of a proline residue at position 249 of the viral NS3 helicase is neither sufficient nor necessary to confer pathogenicity to any given lineage 2 WNV strain in birds.

Phylogenetic characterization of Central/Southern European lineage 2 West Nile virus: analysis of human outbreaks in Italy and Greece, 2013-2014

In recent years, West Nile virus (WNV) lineage 2 has been spreading and causing disease outbreaks in humans and animals in Europe. In order to characterize viral diversity, we performed full-length genome sequencing of WNV lineage 2 from human samples collected during outbreaks in Italy and Greece in 2013 and 2014. Phylogenetic analysis showed that these WNV lineage 2 genomes belonged to a monophyletic clade derived from a single introduction into Europe of the prototype Hungarian strain. Correlation of phylogenetic data with geospatial information showed geographical clustering of WNV genome sequences both in Italy and in Greece, indicating that the virus had evolved and diverged during its dispersal in Europe, leading to the emergence of novel genotypes, as it adapted to local ecological niches. These genotypes carried divergent conserved amino acid substitutions, which might have been relevant for viral adaptation, as suggested by selection pressure analysis and in silico and experimental modelling of sequence changes. In conclusion, the results of this study provide further information on WNV lineage 2 transmission dynamics in Europe, and emphasize the need for WNV surveillance activities to monitor viral evolution and diversity.

Monitoring of West Nile virus in mosquitoes between 2011-2012 in Hungary

West Nile virus (WNV) is a widely distributed mosquito-borne flavivirus. WNV strains are classified into several genetic lineages on the basis of phylogenetic differences. Whereas lineage 1 viruses are distributed worldwide, lineage 2 WNV was first detected outside of Africa in Hungary in 2004. Since then, WNV-associated disease and mortality in animal and human hosts have been documented periodically in Hungary. After the first detection of WNV from a pool of Culex pipiens mosquitoes in 2010, samples were collated from several sources and tested in a 2-year monitoring program. Collection areas were located in the Southern Transdanubium, in northeastern Hungary, in eastern Hungary, and in southeastern Hungary. During the 2 years, 23,193 mosquitoes in 645 pools were screened for WNV virus presence with RT-PCR. Three pools were found positive for WNV in 2011 (one pool of Ochlerotatus annulipes collected in Fényeslitke in June, one pool of Coquillettidia richiardii collected in Debrecen, Fancsika-tó, in July, and one pool of Cx. pipiens captured near Red-Footed Falcon colonies at Kardoskút in September). The minimal infection rate (MIR=proportion of infected mosquitoes per 1000 mosquitoes) of all mosquito pools was 0.25, whereas the MIR of infected species was 2.03 for O. annulipes, 0.63 for C. richiardii, and 2.70 for C.x pipiens. Molecular data have demonstrated that the same lineage 2 WNV strain has circulated in wild birds, horses, humans, and mosquitoes in Hungary since 2004. Mosquito-based surveillance successfully complemented the ongoing, long-term passive surveillance system and it was useful for the early detection of WNV circulation.

The challenge of West Nile virus in Europe: knowledge gaps and research priorities

West Nile virus (WNV) is continuously spreading across Europe, and other continents, i.e. North and South America and many other regions of the world. Despite the overall sporadic nature of outbreaks with cases of West Nile neuroinvasive disease (WNND) in Europe, the spillover events have increased and the virus has been introduced into new areas. The high genetic diversity of the virus, with remarkable phenotypic variation, and its endemic circulation in several countries, require an intensification of the integrated and multidisciplinary research efforts built under the 7th Framework Programme of the European Union (FP7). It is important to better clarify several aspects of WNV circulation in Europe, including its ecology, genomic diversity, pathogenicity, transmissibility, diagnosis and control options, under different environmental and socio-economic scenarios. Identifying WNV endemic as well as infection-free areas is becoming a need for the development of human vaccines and therapeutics and the application of blood and organs safety regulations. This review, produced as a joint initiative among European experts and based on analysis of 118 scientific papers published between 2004 and 2014, provides the state of knowledge on WNV and highlights the existing knowledge and research gaps that need to be addressed with high priority in Europe and neighbouring countries.

Limited susceptibility of mice to Usutu virus (USUV) infection and induction of flavivirus cross-protective immunity

Flaviviruses are RNA viruses that constitute a worrisome threat to global human and animal health. In Europe, West Nile virus (WNV) outbreaks have dramatically increased in number and severity in recent years, with dozens of human and horse deaths and a high avian mortality across the continent. Besides WNV, the only clinically relevant mosquito-borne flavivirus detected so far in Europe has been the Usutu virus (USUV), which after being reported for the first time in Austria in 2001, quickly spread across Europe, causing a considerable number of bird deaths and neurological disorders in a few immunocompromised patients. Even though USUV infects multiple avian species that develop antibodies, there is little information about USUV susceptibility, pathogenicity and cross-reactive immunity. Here, the susceptibility of suckling and adult mice to USUV infection and the induction of cross-protective immunity against WNV challenge have been addressed.

The global ecology and epidemiology of West Nile virus

Since its initial isolation in Uganda in 1937 through the present, West Nile virus (WNV) has become an important cause of human and animal disease worldwide. WNV, an enveloped virus of the genus Flavivirus, is naturally maintained in an enzootic cycle between birds and mosquitoes, with occasional epizootic spillover causing disease in humans and horses. The mosquito vectors for WNV are widely distributed worldwide, and the known geographic range of WNV transmission and disease has continued to increase over the past 77 years. While most human infections with WNV are asymptomatic, severe neurological disease may develop resulting in long-term sequelae or death. Surveillance and preventive measures are an ongoing need to reduce the public health impact of WNV in areas with the potential for transmission.

West Nile virus serosurveillance in pigs, wild boars, and roe deer in Serbia

West Nile virus (WNV) is maintained in nature in an enzootic transmission cycle between birds and mosquitoes, but it also infects many other vertebrates, including humans and horses, in which it can induce severe neurological diseases; however, data about virus circulation in other mammals is scarce. WNV has a history of recent outbreaks in Europe, including Serbia, where it was identified for the first time in 2010 in mosquitoes and in 2012 in birds and humans, being responsible for over 300 confirmed human cases and 35 deaths there along 2013. To assess WNV circulation among mammals in the country, 688 samples obtained from 279 farm pigs, 318 wild boars, and 91 roe deer were investigated for the presence of antibodies to WNV by enzyme-linked immunosorbent assay (ELISA) and viral neutralization test (VNT), and the specificity of their reactivity was assayed against Usutu virus (USUV). ELISA-reactive sera were identified in 43 (15.4%) pigs, 56 (17.6%) wild boars, and 17 (18.7%) roe deer. Of these, 6 (14%), 33 (59%), and 4 (23.5%) respectively, neutralized WNV. One out of the 45 ELISA negative sera tested, from a roe deer, neutralized WNV. Cross-reactivity neutralization test indicated that all deer and pigs neutralizing sera were WNV specific, while in 5 (15.2%) of the wild boar samples the specificity could not be established. Four wild boar sera showed USUV specificity. All these data confirm the circulation of both flaviviruses in Serbia, and highlight the need for the implementation of global coordinated surveillance programs in the region.

Latest developments and challenges in the diagnosis of human West Nile virus infection

West Nile virus (WNV) is a mosquito-borne flavivirus responsible for an increasing number of human outbreaks of neuroinvasive disease in Europe and in North America. Notwithstanding the improvements in the knowledge of virus epidemiology and clinical course of infection and the development of new laboratory tests, the diagnosis of WNV infection remains challenging and many cases still remain unrecognized. WNV genome diversity, transient viremia with low viral load and cross-reactivity with other flaviviruses of the antibodies induced by WNV infection are important hurdles that require the diagnosis to be performed by experienced laboratories. Herein, we present and discuss the novel findings on the molecular epidemiology and clinical features of WNV infection in humans with special focus on Europe, the performance of diagnostic tests and the novel methods that have been developed for the diagnosis of WNV infection. A view on how the field might evolve in the future is also presented.

Emergence of west nile virus lineage 2 in europe: a review on the introduction and spread of a mosquito-borne disease

West Nile virus (WNV) is transmitted by mosquitoes and causes fever and encephalitis in humans, equines, and occasionally wild birds. The virus was first isolated in sub-Saharan Africa where it is endemic. WNV lineage 1 has been responsible for repeated disease outbreaks in the countries of the Mediterranean basin over the past 50 years. This lineage was also introduced into North America in 1999 causing widespread human, equine, and avian mortality. WNV lineage 2, the first WNV lineage to be isolated, was believed to be restricted to sub-Saharan Africa causing a relatively mild fever in humans. However, in 2004, an investigation in Hungary of a case of encephalitis in a wild goshawk (Accipiter gentiles) resulted in the isolation of WNV lineage 2. During the summer of 2004, and in subsequent years, the virus appeared to spread locally throughout Hungary and into neighboring Austria. Subsequently, WNV lineage 2 emerged in Greece in 2010 and in Italy in 2011, involving outbreaks on the Italian mainland and Sardinia. Further spread through the Balkan countries is also suspected. Whole genome sequencing has confirmed that the virus responsible for the outbreaks in Greece and Italy was almost identical to that isolated in Hungary. However, unlike the outbreaks in Hungary, the burden of disease in Mediterranean countries has fallen upon the human population with numerous cases of West Nile fever and a relatively higher mortality rate than in previous outbreaks. The emergence of WNV lineage 2 in Europe, its over-wintering and subsequent spread over large distances illustrates the repeated threat of emerging mosquito-borne diseases. This article will review the emergence of WNV lineage 2 in Europe; consider the pathways for virus spread and the public health implications for the continent.