A novel quantitative multiplex real-time RT-PCR for the simultaneous detection and differentiation of West Nile virus lineages 1 and 2, and of Usutu virus

The key role of Spain in the traffic of West Nile virus lineage 1 strains between Europe and Africa

BACKGROUND

West Nile Virus (WNV) is a zoonotic arbovirus worldwide spread. Seasonal WNV outbreaks occur in the Mediterranean basin since the late 1990's with ever-increasing incidence. In Southern Spain WNV is endemic, as disease foci - caused by WNV lineage 1 (WNV-L1) strains - occur every year. On the contrary, WNV-L2 is the dominant lineage in Europe, so most European WNV sequences available belong to this lineage, WNV-L1 sequences being still scarce.

METHODS

To fill this gap, this study reports the genetic characterisation of 27 newly described WNV-L1 strains, involved in outbreaks affecting wild birds and horses during the last decade in South-Western Spain.

RESULTS

All strains except one belong to the Western Mediterranean-1 sub-cluster (WMed-1), related phylogenetically to Italian, French, Portuguese, Moroccan and, remarkably, Senegalese strains. This sub-cluster persisted, spread and evolved into three distinguishable WMed-1 phylogenetic groups that co-circulated, notably, in the same province (Cádiz). They displayed different behaviours: from long-term persistence and rapid spread to neighbouring regions within Spain, to long-distance spread to different countries, including transcontinental spread to Africa. Among the different introductions of WNV in Spain revealed in this study, some of them succeeded to get established, some extinguished from the territory shortly afterwards. Furthermore, Spain's southernmost province, Cádiz, constitutes a hotspot for virus incursion.

CONCLUSION

Southern Spain seems a likely scenario for emergence of exotic pathogens of African origin. Therefore, circulation of diverse WNV-L1 variants in Spain prompts for an extensive surveillance under a One Health approach.

Arbovirus screening of mosquitoes collected in 2022 in Emilia-Romagna, Italy, with the implementation of a real-time PCR for the detection of Tahyna virus

Several Arboviruses (Arthropod-borne virus) are a concrete health risk. While some arboviruses, such as the West Nile virus (WNV) and the Usutu virus (USUV) are actively surveyed, others are neglected, including the Tahyna virus (TAHV). In this work, we tested - searching for all the three viruses - 37,995 mosquitoes collected in 95 attractive traps, baited by carbon dioxide, distributed in the lowlands of Emilia-Romagna, northern Italy, between 19 July and 12 August 2022. Among the 668 pools obtained, WNV was detected in 45 pools of Culex (Cx.) pipiens and USUV was recorded in 24 pools of the same mosquito; ten of these Cx. pipiens pools tested positive for both WNV and USUV. Interestingly, we recorded a significant circulation of both WNV lineage 1 (WNV-L1) and lineage 2 (WNV-L2): WNV-L1 strains were detected in 40 pools, WNV-L2 strains in three pools and both lineages were detected in two pools. TAHV was detected in 8 different species of mosquitoes in a total of 37 pools: Aedes (Ae.) caspius (25), Ae. albopictus (5), Ae. vexans (3), Cx. pipiens (2), Ae. cinereus (1) and Anopheles maculipennis sl (1). The significant number of Ae. caspius-pools tested positive and the estimated viral load suggest that this mosquito is the principal vector in the surveyed area. The potential involvement of other mosquito species in the TAHV cycle could usefully be the subject of further experimental investigation. The results obtained demonstrate that, with adequate sampling effort, entomological surveillance is able to detect arboviruses circulating in a given area. Further efforts must be made to better characterise the TAHV cycle in the surveyed area and to define health risk linked to this virus.

West Nile virus surveillance using sentinel birds: results of eleven years of testing in corvids in a region of northern Italy

The natural transmission cycle of West Nile virus (WNV) involves birds as primary hosts and mosquitoes as vectors, but this virus can spread to mammals, human beings included. Asymptomatic infected donors pose a risk to the safety of blood transfusions and organ transplants, as WNV can be transmitted through these medical procedures. Since 2009, the region of Emilia-Romagna in northern Italy has been implementing an integrated surveillance system in order to detect WNV circulation in the environment at an early stage. Here we report the results of the two components of the surveillance system, the active testing of corvids and humans, and demonstrate that bird surveillance alone improves a surveillance system based solely on human case detection. As WNV risk reduction measures are applied on a provincial basis, we assessed the ability of this surveillance system component to detect virus circulation prior to the notification of the first human case for each province. Overall, 99 epidemic seasons were evaluated as a result of 11 years (2013-2023) of surveillance in the nine provinces of the region. In this period, 22,314 corvids were tested for WNV and 642 (2.9%) were found to be infected. WNV was generally first detected in birds in July, with sample prevalence peaks occurring between August and September. During the same period, 469 autochthonous human cases were notified, about 60% of which were reported in August. WNV was detected 79 times out of the 99 seasons considered. The virus was notified in birds 73 times (92.4%) and 60 times (75.9%) in humans. WNV was first or only notified in birds in 57 seasons (72.1%), while it was first or only notified in humans in 22 seasons (27.8%). Active surveillance in corvids generally allows the detection of WNV before the onset of human cases. Failure of virus detection occurred mainly in seasons where the number of birds tested was low. Our results show that active testing of a minimum of 3.8 corvids per 100 km2 provides a satisfactory timeliness in the virus detection, but for early detection of WNV it is crucial to test birds between mid-June and mid-August.

Monitoring Aedes populations for arboviruses, Wolbachia, insecticide resistance and its mechanisms in various agroecosystems in Benin

Aedes mosquitoes are the main vectors of arboviruses in Benin. Cases of dengue have been reported in Benin with all four serotypes of the virus actively circulating in this region. Some agricultural settings are known to harbor Aedes vectors responsible for the transmission of arboviruses. The massive use of certain insecticides in agricultural settings has probably contributed to insecticide resistance in these vectors. In Benin, the susceptibility of arbovirus vectors to insecticides is poorly studied. In addition, the distribution of Wolbachia spp., which is used against some arboviruses is unknown. Moreover, there is limited information regarding the vectors responsible for the transmission of arboviruses in Benin. This present study monitored the species composition, arboviruses, and Wolbachia symbiont status, as well as the phenotypic and molecular insecticide resistance profile of Aedes populations from three agroecosystems in Benin. Aedes species identification was performed morphologically and confirmed using qPCR. (RT)-qPCR assay was applied for monitoring the presence of DENV, CHIKV, ZIKV, and WNV pathogens as well as for naturally occurring Wolbachia symbionts. Insecticide resistance was assessed phenotypically, by permethrin (0.75%) exposure of Adults (F0) using World Health Organization (WHO) bioassay protocols, and at the molecular level, using TaqMan (RT)-qPCR assays for assessing knock-down resistance (kdr) mutations (F1534C, V1016G/I, and S989P) and the expression levels of eight detoxification genes (P450s from the CYP9 and CYP6 families, carboxylesterases and glutathione-S-transferases). Aedes aegypti (Ae. aegypti) mosquitoes were the most abundant (93.9%) in the three agroecosystems studied, followed by Aedes albopictus (Ae. albopictus) mosquitoes (6.1%). No arboviruses were detected in the study's mosquito populations. Naturally occurring Wolbachia symbionts were present in 7 pools out of 15 pools tested. This could influence the effectiveness of vector control strategies based on exogenously introduced Wolbachia, all present in the three agroecosystems. Full susceptibility to permethrin was observed in all tested populations of Ae. albopictus. On the contrary, Ae. aegypti were found to be resistant in all three agroecosystem sites except for banana plantation sites, where full susceptibility was observed. Molecular analysis revealed that individual target site resistance kdr mutations F1534C and V1016G/I were detected in most Ae. aegypti populations. Additionally, double mutant (F1534C + V1016G/I) mosquitoes were found in some populations, and in one case, triple mutant (F1534C + V1016G/I + S989P) mosquitoes were detected. Metabolic resistance, as reflected by overexpression of three P450 genes (CYP6BB2, CYP9J26, and CYP9J32), was also detected in Ae. aegypti mosquitoes. Our study provides information that could be used to strategize future vector control strategies and highlights the importance of continuing vector surveillance. Future studies should assess the effect of piperonyl butoxide (PBO) on metabolic resistance and identify the different strains of Wolbachia spp., to choose the best vector control strategies in Benin.

Reoccurrence of West Nile virus lineage 1 after 2-year decline: first equine outbreak in Campania region

West Nile virus (WNV) is the most widespread arbovirus worldwide, responsible for severe neurological symptoms in humans as well as in horses and birds. The main reservoir and amplifier of the virus are birds, and migratory birds seem to have a key role in the introduction and spread of WNV during their migratory routes. WNV lineage 1 (L1) has been missing in Italy for almost 10 years, only to reappear in 2020 in two dead raptor birds in southern Italy. The present study reports the first equine outbreak in the Campania region. A 7-year-old horse died because of worsening neurological signs and underwent necropsy and biomolecular analyses. WNV-L1 was detected by real-time RT-PCR in the heart, brain, gut, liver, and spleen. Next Generation Sequence and phylogenetic analysis revealed that the strain responsible for the outbreak showed a nucleotide identity of over 98% with the strain found in Accipiter gentilis 2 years earlier in the same area, belonging to the WNV-L1 Western-Mediterranean sub-cluster. These results underline that WNV-L1, after reintroduction in 2020, has probably silently circulated during a 2-year eclipse, with no positive sample revealed by both serological and biomolecular examinations in horses, birds, and mosquitoes. The climate changes that have occurred in the last decades are evolving the epidemiology of WNV, with introductions or re-introductions of the virus in areas that were previously considered low risk. Thereby, the virus may easily amplify and establish itself to reappear with sporadic evident cases in susceptible hosts after several months or even years.

Viral RNA in Mosquitoes (Diptera: Culicidae) Collected between 2019 and 2021 in Germany

Due to globalisation and climate change, mosquito-borne pathogens are emerging in new areas on all continents, including Europe, which has recently faced outbreaks of dengue, chikungunya and West Nile fever. The present study complements previous investigations to evaluate the circulation of mosquito-borne viruses in Germany, with the aim of identifying potential vector species and risk areas. Mosquitoes collected from 2019 to 2021 and identified to species or species group level were screened for viruses of the families Flaviviridae, Peribunyaviridae and the genus Alphavirus of the family Togaviridae. In total, 22,528 mosquitoes were examined, thus providing the most comprehensive study on West Nile virus (WNV) circulation so far in the German mosquito population. Usutu virus (USUV) RNA was detected in six samples, Sindbis virus (SINV) RNA in 21 samples and WNV RNA in 11 samples. Samples containing RNA of USUV and WNV consisted of mosquitoes collected in the East German federal states of Brandenburg, Saxony and Saxony-Anhalt, while samples with RNA of SINV originated from more widespread locations. Although minimum infection rates have remained relatively low, the intensity of virus circulation appears to be increasing compared to previous studies. Continuous mosquito screening contributes to the early detection of the introduction and spread of mosquito-borne pathogens.

Spatial and temporal dynamics of West Nile virus between Africa and Europe

It is unclear whether West Nile virus (WNV) circulates between Africa and Europe, despite numerous studies supporting an African origin and high transmission in Europe. We integrated genomic data with geographic observations and phylogenetic and phylogeographic inferences to uncover the spatial and temporal viral dynamics of WNV between these two continents. We focused our analysis towards WNV lineages 1 (L1) and 2 (L2), the most spatially widespread and pathogenic WNV lineages. Our study shows a Northern-Western African origin of L1, with back-and-forth exchanges between West Africa and Southern-Western Europe; and a Southern African origin of L2, with one main introduction from South Africa to Europe, and no back introductions observed. We also noticed a potential overlap between L1 and L2 Eastern and Western phylogeography and two Afro-Palearctic bird migratory flyways. Future studies linking avian and mosquito species susceptibility, migratory connectivity patterns, and phylogeographic inference are suggested to elucidate the dynamics of emerging viruses.

Detection of West Nile and Usutu Virus RNA in Autumn Season in Wild Avian Hosts in Northern Italy

West Nile (WNV) and Usutu (USUV) viruses are two mosquito-borne viruses belonging to the family Flaviviridae and genus Flavivirus. The natural transmission cycle of WNV and USUV involves mosquitoes and birds, while mammals are thought to be accidental hosts. The goal of this study was to report-in the context of "off-season monitoring" and passive surveillance-the detection of WNV and USUV RNA in wild birds. To this end, we analyzed biological samples of wild birds in Northern Italy, from October to May, hence outside of the regional monitoring period (June-September). The virological investigations for the detection of USUV and WNV RNA were performed using real-time PCR on frozen samples of the brain, myocardium, kidney, and spleen. In a total sample of 164 wild birds belonging to 27 different species, sequences of both viruses were detected: four birds (2.44%) were positive for WNV and five (3.05%) for USUV. Off-season infections of WNV and especially USUV are still widely discussed and only a few studies have been published to date. To the best of our knowledge, this study is the first report on the detection of USUV RNA until December 22nd. Although further studies are required, our results confirm the viral circulation out-of-season of Flavivirus in wild birds, suggesting reconsidering the epidemiological monitoring period based on each individual climate zone and taking into consideration global warming which will play an important role in the epidemiology of vector-borne diseases.

West Nile Virus Lineage 2 in Free-Living Corvus cornix Birds in Poland

The summer temperatures recorded in Poland in 2022 were among the highest in over 30 years and, combined with higher-than-expected rainfall, gave the impression of an almost tropical climate. Such climatic conditions were ideal for the transmission of vector-borne zoonotic diseases such as West Nile fever. In northeastern Poland, in the Mazowieckie region, the Polish event-based surveillance network reported increased fatalities of free-living hooded crows (Corvus corone cornix). West Nile virus (WNV) lineage 2 was identified for the first time as the etiological agent responsible for the death of the birds. WNV was detected in 17 out of the 99 (17.17%) free-living birds tested in this study. All the WNV-infected dead birds were collected in the same area and were diagnosed in September by the NVRI and confirmed by the EURL for equine diseases, ANSES, in October 2022. Unnaturally high temperatures recorded in Poland in 2022 likely favored the infection and spread of the virus in the avian population. A nationwide alert and awareness raising of blood transfusion centers and hospitals was carried out to prevent human infections by WNV.

Experimental infections in red-legged partridges reveal differences in host competence between West Nile and Usutu virus strains from Southern Spain

Introduction

West Nile virus (WNV) and Usutu virus (USUV) are emerging zoonotic arboviruses sharing the same life cycle with mosquitoes as vectors and wild birds as reservoir hosts. The main objective of this study was to characterize the pathogenicity and course of infection of two viral strains (WNV/08 and USUV/09) co-circulating in Southern Spain in a natural host, the red-legged partridge (Alectoris rufa), and to compare the results with those obtained with the reference strain WNV/NY99.

Methods

WNV inoculated birds were monitored for clinical and analytical parameters (viral load, viremia, and antibodies) for 15 days post-inoculation.

Results and discussion

Partridges inoculated with WNV/NY99 and WNV/08 strains showed clinical signs such as weight loss, ruffled feathers, and lethargy, which were not observed in USUV/09-inoculated individuals. Although statistically significant differences in mortality were not observed, partridges inoculated with WNV strains developed significantly higher viremia and viral loads in blood than those inoculated with USUV. In addition, the viral genome was detected in organs and feathers of WNV-inoculated partridges, while it was almost undetectable in USUV-inoculated ones. These experimental results indicate that red-legged partridges are susceptible to the assayed Spanish WNV with pathogenicity similar to that observed for the prototype WNV/NY99 strain. By contrast, the USUV/09 strain was not pathogenic for this bird species and elicited extremely low viremia levels, demonstrating that red-legged partridges are not a competent host for the transmission of this USUV strain.

Novel Amplicon-Based Sequencing Approach to West Nile Virus

West Nile virus is a re-emerging arbovirus whose impact on public health is increasingly important as more and more epidemics and epizootics occur, particularly in America and Europe, with evidence of active circulation in Africa. Because birds constitute the main reservoirs, migratory movements allow the diffusion of various lineages in the world. It is therefore crucial to properly control the dispersion of these lineages, especially because some have a greater health impact on public health than others. This work describes the development and validation of a novel whole-genome amplicon-based sequencing approach to West Nile virus. This study was carried out on different strains from lineage 1 and 2 from Senegal and Italy. The presented protocol/approach showed good coverage using samples derived from several vertebrate hosts and may be valuable for West Nile genomic surveillance.

First Detection and Molecular Characterization of Usutu Virus in Culex pipiens Mosquitoes Collected in Romania

Usutu virus (USUV) is an emergent arbovirus in Europe causing mortality in bird populations. Similar to West Nile virus (WNV), USUV is maintained in sylvatic cycles between mosquito vectors and bird reservoirs. Spillover events may result in human neurological infection cases. Apart from indirect evidence provided by a recent serological study in wild birds, the circulation of USUV in Romania was not assessed. We aimed to detect and molecular characterize USUV circulating in mosquito vectors collected in South-Eastern Romania-a well-known WNV endemic region-during four transmission seasons. Mosquitoes were collected from Bucharest metropolitan area and Danube Delta, pooled, and screened by real-time RT-PCR for USUV. Partial genomic sequences were obtained and used for phylogeny. USUV was detected in Culex pipiens s.l. female mosquitoes collected in Bucharest, in 2019. The virus belonged to Europe 2 lineage, sub-lineage EU2-A. Phylogenetic analysis revealed high similarity with isolates infecting mosquito vectors, birds, and humans in Europe starting with 2009, all sharing common origin in Northern Italy. To our knowledge, this is the first study characterizing a strain of USUV circulating in Romania.

Identification of Usutu Virus Africa 3 Lineage in a Survey of Mosquitoes and Birds from Urban Areas of Western Spain

Usutu virus (USUV) is an emerging zoonotic arbovirus that has caused an increasing number of animal and human cases in Europe in recent years. Understanding the vector species and avian hosts involved in the USUV enzootic cycle in an area of active circulation is vital to anticipate potential outbreaks. Mosquitoes were captured in 2020, while wild birds were sampled in both 2020 and 2021 in Extremadura, southwestern Spain. The presence of USUV in the mosquito vectors was assessed by a real-time reverse transcription-polymerase chain reaction (rRT-PCR) assay and confirmed by sequencing amplicons from two generic RT-PCR sets for flaviviruses. Sequences were analysed phylogenetically. Bird sera were screened for flavivirus antibodies with a blocking ELISA kit and subsequently tested for virus-specific antibodies with a micro-virus-neutralization test. Overall, 6,004 mosquitoes belonging to 13 species were captured, including some well-known flavivirus vectors (Culex pipiens, Cx. perexiguus, and Cx. univittatus). Of the 438 pools tested, USUV was detected in two pools of Cx. pipiens. Phylogenetic analysis using a fragment of the NS5 gene assigned the USUV detected the Africa 3 lineage. Out of 1,413 wild birds tested, USUV-specific antibodies were detected in 17 birds (1.2%, 10 males and 7 females) from eight species. The first detection of USUV Africa 3 lineage in mosquitoes from Spain, together with serologically positive resident wild birds in urban and rural areas, indicates active circulation and a possible risk of exposure for the human population, with necessity to establish specific surveillance plans.

Risk Factors for Exposure of Wild Birds to West Nile Virus in A Gradient of Wildlife-Livestock Interaction

West Nile virus (WNV) transmission rate is shaped by the interaction between virus reservoirs and vectors, which may be maximized in farm environments. Based on this hypothesis, we screened for WNV in wild birds in three scenarios with decreasing gradient of interaction with horses: (i) the farm (A₁); (ii) the neighborhood (A₂); and (iii) a wild area (A₃). We captured wild birds and analyzed their sera for WNV antibodies by blocking ELISA and micro-virus neutralization test. Flavivirus infections were tested with generic and specific PCR protocols. We parameterized linear mixed models with predictors (bird abundance and diversity, vector abundance, vector host abundance, and weather quantities) to identify Flavivirus spp. and WNV exposure risk factors. We detected a low rate of Flavivirus infections by PCR (0.8%) and 6.9% of the birds were seropositive by ELISA. Exposure to Flavivirus spp. was higher in A₁ (9%) than in A₂ and A₃ (5.6% and 5.8%, respectively). Bird diversity was the most relevant predictor of exposure risk and passerines dominated the on-farm bird community. Our results suggest that measures deterring the use of the farm by passerines should be implemented because the environmental favorability of continental Mediterranean environments for WNV is increasing and more outbreaks are expected.

Epidemiological and Evolutionary Analysis of West Nile Virus Lineage 2 in Italy

West Nile virus (WNV) is a mosquito-borne virus potentially causing serious illness in humans and other animals. Since 2004, several studies have highlighted the progressive spread of WNV Lineage 2 (L2) in Europe, with Italy being one of the countries with the highest number of cases of West Nile disease reported. In this paper, we give an overview of the epidemiological and genetic features characterising the spread and evolution of WNV L2 in Italy, leveraging data obtained from national surveillance activities between 2011 and 2021, including 46 newly assembled genomes that were analysed under both phylogeographic and phylodynamic frameworks. In addition, to better understand the seasonal patterns of the virus, we used a machine learning model predicting areas at high-risk of WNV spread. Our results show a progressive increase in WNV L2 in Italy, clarifying the dynamics of interregional circulation, with no significant introductions from other countries in recent years. Moreover, the predicting model identified the presence of suitable conditions for the 2022 earlier and wider spread of WNV in Italy, underlining the importance of using quantitative models for early warning detection of WNV outbreaks. Taken together, these findings can be used as a reference to develop new strategies to mitigate the impact of the pathogen on human and other animal health in endemic areas and new regions.

Detection of viruses from feces of wild endangered Macaca maura: a potential threat to moor macaque survival and for zoonotic infection

BACKGROUND

To date, there is a scarcity of information and literature on Macaca maura health status relative to viral diseases. The objectives of the present study were to investigate on the potential spread of enteric and non-enteric viruses shed in the environment through a wild macaque feces and to understand the possible interrelation in the spread of zoonotic viruses in a poorly studied geographical area, the Sulawesi Island. This study will also contribute providing useful information on potential threats to the health of this endangered species.

METHODS

The sampling was conducted between 2014 and 2016 in the Bantimurung Bulusaraung National Park, in the south of the Sulawesi Island and non-invasive sampling methods were used to collect fresh stools of the M. maura, one of the seven macaque species endemic to the island of Sulawesi, Indonesia. The population under study consisted in two wild, neighboring social macaque groups with partially overlapping home ranges; twenty-four samples were collected and examined using negative staining electron microscopy and a panel of PCR protocols for the detection of ten RNA and two DNA viruses.

RESULTS

Viral particles resembling parvovirus (5 samples), picornavirus (13 samples) and calicivirus (13 samples) were detected by electron microscopy whereas the PCR panel was negative for the 12 viruses investigated, except for one sample positive for a mosquito flavivirus. The results did not correlate with animal sex; furthermore, because all of the animals were clinically healthy, it was not possible to correlate feces consistency with viral presence.

CONCLUSIONS

As information on viral infections in wild moor macaques remains limited, further studies are yet required to identify the fecal-oral and blood transmitted potentially zoonotic viruses, which may infect the moor macaque and other macaque species endemic to the South Sulawesi Island.

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.

Arbovirus Screening in Mosquitoes in Emilia-Romagna (Italy, 2021) and Isolation of Tahyna Virus

Several viruses can be transmitted by mosquitoes. We searched some of these viruses in 20,778 mosquitoes, collected in 95 traps on the plains of Emilia-Romagna (North of Italy) in 2021. We detected West Nile virus (WNV) and Usutu virus (USUV) in pools of Culex (Cx.) pipiens. In addition, we detected two insect-specific flaviviruses in three pools of Aedes (Ae.) caspius and in two of Ae. vexans. Tahyna virus (TAHV) was detected in six pools, three of Ae. caspius and three of Cx. pipiens, and one isolated strain was obtained from one of the Ae. caspius pools. Moreover, we detected TAHV in pools of several mosquito species (Ae. caspius, Ae. vexans, Ae. albopictus, Anopheles maculipennis s.l.) collected in the previous year of surveillance. Our data indicate Ae. caspius as the species most infected with TAHV in the surveyed area. Together with the likely plasticity of the cycle, we reported strong genome stability of the TAHV, probably linked to a successful adaptation of the virus to its ecological niche. Interestingly, in six pools of Cx. pipiens we detected two associated viruses among USUV, WNV, TAHV and all the three viruses in two pools. This result allows us to assume the presence of particular conditions that prompt the circulation of arboviruses, creating the conditions for viral hot spots. While no human diseases related to Tahyna virus were reported in Italy, its detection over the years suggests that it is worth investigating this virus as a potential cause of disease in humans in order to assess its health burden. IMPORTANCE We reported in this work the detection of three Arboviruses (Arthropod-borne viruses) in mosquitoes collected in Emilia-Romagna in 2021. In addition to West Nile and Usutu viruses, which were reported from more than 10 years in the study area, we detected and isolated Tahyna virus (TAHV). We also reported detections of TAHV obtained in previous years of surveillance in different species of mosquitoes. TAHV is the potential causative agent of summer influenza-like diseases and also of meningitis. Even if human cases of disease referable to this virus are not reported in Italy, its relevant presence in mosquitoes suggests investigating the possibility they could.

Health Status of the Eastern Grey Squirrel (Sciurus carolinensis) Population in Umbria: Results of the LIFE Project 'U-SAVEREDS'

Simple Summary

Invasive alien species are non-native species introduced deliberately or unintentionally beyond their past or present natural distribution, and their introduction and spread threatens local biological diversity. The Eastern grey squirrel is native to North America and was introduced to the British Islands, Italy, and South Africa. Around the year 2000, a new population of grey squirrels was recorded in Perugia, central Italy, where the species populated an area of approximately 50 km², both in woodland and urban areas. The Eastern grey squirrel represents a huge threat to the conservation of the native Eurasian red squirrel when the two species coexist. Moreover, given their confident behaviour with humans, the non-native squirrels can negatively impact public health. The U-SAVEREDS Project was set up for Eurasian red squirrel conservation in Umbria through the eradication of the alien species and it also provided information on the health status of the Eastern grey squirrel to identify any infectious agents. The recovery of zoonotic pathogens allowed to assess the Eastern grey squirrel’s impact on human and domestic and wild animals’ health, provide helpful feedback for the management and eradication procedures, and raise public awareness through environmental education.

Abstract

The introduction of the Eastern grey squirrel (Sciurus carolinensis) in Europe is one of the best-known cases of invasive alien species (IAS) colonisation, that poses a severe risk to the conservation of biodiversity. In 2003, it was released in a private wildlife park near the city of Perugia (Italy), where it is replacing the native Eurasian red squirrel (Sciurus vulgaris). The LIFE13 BIO/IT/000204 Project (U-SAVEREDS) was set up for the Sciurus vulgaris conservation in Umbria through an eradication campaign of grey squirrels. One hundred and fifty-four animals were analysed for bacteriological, mycological, virological, and serological investigations (C4 action). Sanitary screening showed that Sciurus carolinensis is a dermatophyte carrier, and therefore, it could cause public health issues for humans, considering its confident behaviour. Moreover, it has been marginally responsible for the spreading of Candida albicans, Coxiella burnetii, and Borrelia lusitaniae. Health status evaluation conducted on the Sciurus carolinensis population indicated that it is necessary to raise awareness of its impacts on biodiversity and human health. Moreover, the health status and behaviours of the IAS must be considered when control or eradication campaigns are planned.

Direct and Indirect Role of Migratory Birds in Spreading CCHFV and WNV: A Multidisciplinary Study on Three Stop-Over Islands in Italy

The annual movements of migratory birds can contribute to the spread of African ticks and tick-borne pathogens of potential public health concern across Europe. The aim of the study was to investigate their role in the possible introduction of African ticks and tick-borne pathogens into European countries during spring migration. A total of 2344 ticks were collected during three spring seasons from 1079 birds captured on three Italian stop-over islands during their northbound migration. Once identified, each tick was tested by RT-PCR for the presence of Crimean-Congo hemorrhagic fever (CCHFV), West Nile (WNV), and Usutu (USUV) viruses. Moreover, carcasses of birds found dead were collected and tested for the possible presence of WNV and USUV. Results confirmed a higher contribution of trans-Saharan migrants compared to intra-Palearctic ones and the prevalence of African tick species in the sample. CCHFV was detected for the second time in Italy in a Hyalomma rufipes, and WNV was found in two ticks of the same genus, all carried by trans-Saharan birds. WNV lineage 1 was also found in the organs of a Garden warbler. These results confirm the role of migratory birds in carrying African ticks, as well as viruses of zoonotic importance, from Africa into Europe.

West Nile Virus and Usutu Virus: A Post-Mortem Monitoring Study in Wild Birds from Rescue Centers, Central Italy

West Nile virus (WNV) and Usutu virus (USUV) are mosquito-borne flaviviruses that have been associated with neurological diseases in humans and wild birds. Wild bird rescue centers are potential significant hot spots for avian infection surveillance, as recognized in the Italian Integrate National Surveillance Plan for Arboviruses. Here we report the results of a post-mortem active monitoring study conducted from November 2017 to October 2020 on animals hosted in five wild bird rescue centers of Central Italy. Five hundred seventy-six (n = 576) wild birds were tested by real-time polymerase chain reaction (RT-PCR) for the presence of WNV or USUV RNA fragments. No birds tested positive for USUV RNA (n = 0; 0.00%). Evidence of WNV RNA (Ct value = 34.36) was found in one bird (n = 1; 0.17%), an adult little grebe (Tachybaptus ruficollis subsp. ruficollis), that tested WNV positive in December 2019. This study highlights the strategic role of wildlife rescue centers in monitoring both the introduction and circulation of avian emerging zoonotic diseases. In addition, the presence of WNV during the cold season evidences the possible role of birds in overwintering mechanisms in the Italian territory and requires further investigations.

West Nile Virus Lineage 2 Overwintering in Italy

In January 2022, West Nile virus (WNV) lineage 2 (L2) was detected in an adult female goshawk rescued near Perugia in the region of Umbria (Italy). The animal showed neurological symptoms and died 15 days after its recovery in a wildlife rescue center. This was the second case of WNV infection recorded in birds in the Umbria region during the cold season, when mosquitoes, the main WNV vectors, are usually not active. According to the National Surveillance Plan, the Umbria region is included amongst the WNV low-risk areas. The necropsy evidenced generalized pallor of the mucous membranes, mild splenomegaly, and cerebral edema. WNV L2 was detected in the brain, heart, kidney, and spleen homogenate using specific RT-PCR. Subsequently, the extracted viral RNA was sequenced. A Bayesian phylogenetic analysis performed through a maximum-likelihood tree showed that the genome sequence clustered with the Italian strains within the European WNV strains among the central-southern European WNV L2 clade. These results, on the one hand, confirmed that the WNV L2 strains circulating in Italy are genetically stable and, on the other hand, evidenced a continuous WNV circulation in Italy throughout the year. In this report case, a bird-to-bird WNV transmission was suggested to support the virus overwintering. The potential transmission through the oral route in a predatory bird may explain the relatively rapid spread of WNV, as well as other flaviviruses characterized by similar transmission patterns. However, rodent-to-bird transmission or mosquito-to-bird transmission cannot be excluded, and further research is needed to better understand WNV transmission routes during the winter season in Italy.

West Nile Virus Occurrence and Ecological Niche Modeling in Wild Bird Species and Mosquito Vectors: An Active Surveillance Program in the Peloponnese Region of Greece

West Nile Virus (WNV) is maintained in nature in a bird-mosquito cycle and human infections follow a seasonal pattern, favored by climatic conditions. Peloponnese Region, located in Southern Greece, initiated an active WNV surveillance program to protect public health during 2019–2020. The project included monitoring of avian hosts and mosquito vectors, while sampling locations were prioritized after consideration of WNV circulation in birds, mosquitos and humans during previous seasons. Biological materials were collected from 493 wild birds of 25 species and 678 mosquito pools, which were molecularly screened for WNV presence. In this case, 14 environmental variables were associated with WNV detection in wild birds and mosquitos by using two separate MaxEnt models. Viral RNA was not detected in the target species during 2019, although in 2020, it was reported on 46 wild birds of ten species and 22 mosquito pools (Culex pipiens and Aedes albopictus). Altitude and land uses were significant predictors for both models and in fact, suitable conditions for virus occurrence were identified in low altitude zones. Bird- and mosquito-based surveillance systems yielded similar results and allowed for targeted vector control applications in cases of increased virus activity. Human cases were not reported on Peloponnese in 2020.

Usutu virus in blackbirds (Turdus merula) with clinical signs, a case study from northern Italy

Usutu virus (USUV) is a mosquito-borne virus belonging to the family Flaviviridae, genus Flavivirus. Natural transmission cycle of USUV involves mosquitoes and birds, so humans and other mammals are considered incidental hosts. In this study, USUV infection was diagnosed in all wild blackbirds, collected from July to September 2018 in a wildlife recovery center in the province of Bologna, in the Emilia-Romagna region, northern Italy. All blackbirds showed neurological clinical signs, such as overturning, pedaling, and incoordination. Moreover, the subjects died shortly after arriving at the hospitalization center. Virological investigations were performed by real-time PCR on frozen samples of the spleen, kidney, myocardium, and brain for the detection of Usutu (USUV) and West Nile (WNV) viruses. The small and large intestine were used as a matrix for the detection of Newcastle disease virus (NDV). All 56 subjects with neurological clinical signs were positive for USUV, only one subject (1.8%) tested positive for WNV, and no subject was positive for NDV. The most represented age class was class 1 J (58.9%), followed by class 3 (25.0%), and lastly from class 4 (16.1%). Most of the blackbirds before dying were in good (51.8%) and fair (39.3%) nutritional status, while only five subjects (8.9%) were cachectic. The USUV genomes detected in the blackbirds of this study fall within the sub-clade already called EU2 that has been detected since 2009 in the Emilia-Romagna region. Neurological clinical signs in USUV-affected blackbirds are still widely discussed and there are few works in the literature. Although our results require further studies, we believe them to be useful for understanding the clinical signs of Usutu virus in blackbirds, helping to increase the knowledge of this zoonotic agent in wild species and to understand its effect on the ecosystem. The goal of this study was to report—in the context of the regional passive surveillance program—the detection of USUV RNA in its most important amplifying host, the common blackbird, when showing clinical signs before death.

Mosquito population structure, pathogen surveillance and insecticide resistance monitoring in urban regions of Crete, Greece

Background

In Greece vector borne diseases (VBD) and foremost West Nile virus (WNV) pose an important threat to public health and the tourist industry, the primary sector of contribution to the national economy. The island of Crete, is one of Greece’s major tourist destinations receiving annually over 5 million tourists making regional VBD control both a public health and economic priority.

Methodology

Under the auspices of the Region of Crete, a systematic integrative surveillance network targeting mosquitoes and associated pathogens was established in Crete for the years 2018–2020. Using conventional and molecular diagnostic tools we investigated the mosquito species composition and population dynamics, pathogen infection occurrences in vector populations and in sentinel chickens, and the insecticide resistance status of the major vector species.

Principal findings

Important disease vectors were recorded across the island including Culex pipiens, Aedes albopictus, and Anopheles superpictus. Over 75% of the sampled specimens were collected in the western prefectures potentially attributed to the local precipitation patterns, with Cx. pipiens being the most dominant species. Although no pathogens (flaviviruses) were detected in the analysed mosquito specimens, chicken blood serum analyses recorded a 1.7% WNV antibody detection rate in the 2018 samples. Notably detection of the first WNV positive chicken preceded human WNV occurrence in the same region by approximately two weeks. The chitin synthase mutation I1043F (associated with high diflubenzuron resistance) was recorded at an 8% allelic frequency in Lasithi prefecture Cx. pipiens mosquitoes (sampled in 2020) for the first time in Greece. Markedly, Cx. pipiens populations in all four prefectures were found harboring the kdr mutations L1014F/C/S (associated with pyrethroid resistance) at a close to fixation rate, with mutation L1014C being the most commonly found allele (≥74% representation). Voltage gated sodium channel analyses in Ae. albopictus revealed the presence of the kdr mutations F1534C and I1532T (associated with putative mild pyrethroid resistance phenotypes) yet absence of V1016G. Allele F1534C was recorded in all prefectures (at an allelic frequency range of 25–46.6%) while I1532T was detected in populations from Chania, Rethymnon and Heraklion (at frequencies below 7.1%). Finally, no kdr mutations were detected in the Anopheles specimens included in the analyses.

Conclusions/Significance

The findings of our study are of major concern for VBD control in Crete, highlighting (i) the necessity for establishing seasonal integrated entomological/pathogen surveillance programs, supporting the design of targeted vector control responses and; ii) the need for establishing appropriate insecticide resistance management programs ensuring the efficacy and sustainable use of DFB and pyrethroid based products in vector control.

The island of Crete, is one of Greece’s major tourist destinations, receiving over 5 million tourists annually, making control of vector borne diseases (VBD) like West Nile virus (WNV) both a public health and economic priority. A comprehensive surveillance network targeting mosquitoes and associated pathogens was established in Crete for the years 2018–2020. Important disease vectors (Culex pipiens, Aedes albopictus and Anopheles superpictus) were recorded across the island. The presence of WNV antibodies in sentinel chickens was also recorded and, notably, preceded human WNV occurrence in the same region by approximately two weeks. Mutations associated with resistance to insecticides used for vector control were also detected; most importantly the chitin synthase mutation I1043F (associated with high diflubenzuron resistance) was recorded for the first time in Greece. The findings of our study are of major concern for VBD control in Greece (and Crete specifically), highlighting (i) the necessity for establishing seasonal surveillance programs and ii) the need for establishing appropriate insecticide resistance management programs for sustainable vector control.

West Nile and Usutu Virus Introduction via Migratory Birds: A Retrospective Analysis in Italy

The actual contribution of migratory birds in spreading West Nile (WNV) and Usutu virus (USUV) across Europe and from Africa to old countries is still controversial. In this study, we reported the results of molecular and serological surveys on migrating birds sampled during peaks of spring and autumn migration at 11 Italian sites located along important flyways, from 2012 to 2014. A total of 1335 specimens made of individual or pooled sera, and organs from 275 dead birds were tested for WNV and USUV RNA by real time PCR (RT-PCR). Furthermore, sera were tested by serum neutralization assay for detecting WNV and USUV neutralizing antibodies. Molecular tests detected WNV lineage 2 RNA in a pool made of three Song Thrush (Turdus philomelos) sera sampled in autumn, and lineage 1 in kidneys of six trans-Saharan birds sampled in spring. Neutralizing antibodies against WNV and USUV were found in 5.80% (n = 72; 17 bird species) and 0.32% (n = 4; 4 bird species) of the tested sera, respectively. Our results do not exclude the role of migratory birds as potential spreaders of WNV and USUV from Africa and Central Europe to Mediterranean areas and highlight the importance of a more extensive active surveillance of zoonotic viruses.

West Nile Virus Lineage 1 in Italy: Newly Introduced or a Re-Occurrence of a Previously Circulating Strain?

In Italy, West Nile virus (WNV) appeared for the first time in the Tuscany region in 1998. After 10 years of absence, it re-appeared in the areas surrounding the Po River delta, affecting eight provinces in three regions. Thereafter, WNV epidemics caused by genetically divergent isolates have been documented every year in the country. Since 2018, only WNV Lineage 2 has been reported in the Italian territory. In October 2020, WNV Lineage 1 (WNV-L1) re-emerged in Italy, in the Campania region. This is the first occurrence of WNV-L1 detection in the Italian territory since 2017. WNV was detected in the internal organs of a goshawk (Accipiter gentilis) and a kestrel (Falco tinnunculus). The RNA extracted in the goshawk tissue samples was sequenced, and a Bayesian phylogenetic analysis was performed by a maximum-likelihood tree. Genome analysis, conducted on the goshawk WNV complete genome sequence, indicates that the strain belongs to the WNV-L1 Western-Mediterranean (WMed) cluster. Moreover, a close phylogenetic similarity is observed between the goshawk strain, the 2008-2011 group of Italian sequences, and European strains belonging to the Wmed cluster. Our results evidence the possibility of both a new re-introduction or unnoticed silent circulation in Italy, and the strong importance of keeping the WNV surveillance system in the Italian territory active.

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.

First neuroinvasive human case of West Nile Disease in Southern Italy: Results of the 'One Health' approach

Background

West Nile Disease (WND) is a zoonotic mosquito‐borne infection involving viral pathogens, human and animal hosts, vectors and environment. Cooperation among medical, veterinary and entomological fields has been promoted by the Italian Public Health Authorities, and an integrated West Nile Virus (WNV) Surveillance Plan has been in force in Italy since 2016 to prevent the transmission risk of WND to humans through an early detection of viral circulation by animal and entomological surveillance. This managing model is unique in Europe.

Objectives

This survey aimed at presenting the ‘One Health’ approach applied in 2016 to the first autochthonous human case of West Nile Neuroinvasive Disease (WNND) in Sicily (Southern Italy).

Methods

Serological (anti‐WNV IgM and IgG ELISA, anti‐WNV neutralizing antibodies) and molecular tests were conducted on blood, liquor and urine of a 38‐year‐old man with encephalitis and meningitis. Overall, 2704 adult culicides from 160 mosquito catches were morphologically identified. Female mosquitoes were analysed in pools for WNV RNA detection. Serological (anti‐WNV IgM and IgG ELISA) and molecular analyses for WNV were carried out in 11 horses, 271 chickens and two dogs sampled in farms around the man's residence.

Results and conclusions

WNND was confirmed by serological analysis on patient's liquor and serum. Collected mosquito species included Culex pipiens (93.56%, CI_95% 92.64%–94.49%), Aedes albopictus (5.25%, CI_95% 4.41%–6.09%), Culex hortensis (0.59%, CI_95% 0.30%–0.88%), Culiseta longiareolata (0.55%, CI_95% 0.27%–0.83%) and Anopheles maculipennis s.l. (0.04%, CI_95% –0.04% to 0.11%). Mosquito pools were negative for WNV RNA. Two dogs (100%) and two horses (18.18%, CI_95% –4.61 to 40.97%) resulted positive for anti‐WNV specific antibodies.

The ‘One Health’ approach allowed to report the first human neuroinvasive WND in Sicily and to confirm the local circulation of WNV in animals of the same area where the clinical case occurred, defining the autochthonous origin of the infection.

A panel of real-time PCR assays for the detection of Bourbon virus, Heartland virus, West Nile virus, and Trypanosoma cruzi in major disease-transmitting vectors

Vector-borne pathogens, such as Bourbon virus (BRBV), Heartland virus (HRTV), West Nile virus (WNV), and Trypanosoma cruzi (TCZ) are a great threat to public health and animal health. We developed a panel of TaqMan real-time PCR assays for pathogen surveillance. PCR targets were selected based on nucleic acid sequences deposited in GenBank. Primers and probes were either designed de novo or selected from publications. The coverages and specificities of the primers and probes were extensively evaluated by performing BLAST searches. Synthetic DNA or RNA fragments (gBlocks) were used as PCR templates in initial assay development and PCR positive controls in subsequent assay validation. For operational efficiency, the same thermocycling profile was used in BRBV, HRTV, and WNV reverse-transcription quantitative PCR (RT-qPCR) assays, and a similar thermocycling profile without the initial reverse-transcription step was used in TCZ qPCR. The assays were optimized by titrating primer and probe concentrations. The analytical sensitivities were 100, 100, 10, and 10 copies of gBlock per reaction for BRBV (Cq = 36.0 ± 0.7), HRTV (Cq = 36.6 ± 0.9), WNV (Cq = 35.5 ± 0.4), and TCZ (Cq = 38.8 ± 0.3), respectively. PCR sensitivities for vector genomic DNA or RNA spiked with gBlock reached 100, 100, 10, and 10 copies per reaction for BRBV, HRTV, WNV, and TCZ, respectively. PCR specificity evaluated against a panel of non-target pathogens showed no significant cross-reactivity. Our BRBV, HRTV, WNV, and TCZ PCR panel could support epidemiologic studies and pathogen surveillance.

West Nile and Usutu Viruses' Surveillance in Birds of the Province of Ferrara, Italy, from 2015 to 2019

West Nile (WNV) and Usutu (USUV) viruses are mosquito-borne flaviviruses. Thanks to their importance as zoonotic diseases, a regional plan for surveillance of Arboviruses was implemented in Emilia-Romagna in 2009. The province of Ferrara belongs to the Emilia-Romagna region, and it is an endemic territory for these viruses, with favorable ecological conditions for abundance of mosquitoes and wild birds. From 2015 to 2019, we collected 1842 dead-found birds at a wildlife rehabilitation center, which were analysed by three different PCRs for the detection of WNV and USUV genomes. August was characterized by the highest infection rate for both viruses. Columbiformes scored the highest USUV prevalence (8%), while Galliformes and Strigiformes reported the highest prevalence for WNV (13%). Among Passeriformes (the most populated Order), Turdus merula was the most abundant species and scored the highest prevalence for both viruses. To optimize passive surveillance plans, monitoring should be focused on the summer and towards the avian species more prone to infection by both viruses.

West Nile and Usutu viruses co-circulation in central Italy: outcomes of the 2018 integrated surveillance

BACKGROUND

West Nile (WNV) and Usutu (USUV) are emerging vector-borne zoonotic flaviviruses. They are antigenically very similar, sharing the same life cycle with birds as amplification host, Culicidae as vector, and man/horse as dead-end host. They can co-circulate in an overlapping geographic range. In Europe, surveillance plans annually detect several outbreaks.

METHODS

In Italy, a WNV/USUV surveillance plan is in place through passive and active surveillance. After a 2018 WNV outbreak, a reinforced integrated risk-based surveillance was performed in four municipalities through clinical and serological surveillance in horses, Culicidae catches, and testing on human blood-based products for transfusion.

RESULTS

Eight WNV cases in eight equine holdings were detected. Twenty-three mosquitoe catches were performed and 2367 specimens of Culex pipiens caught; 17 pools were USUV positive. A total of 8889 human blood donations were tested, and two asymptomatic donors were USUV positive.

CONCLUSIONS

Different surveillance components simultaneously detected WNV only in horses and USUV only in humans and mosquitoes. While in endemic areas (i.e. northern Italy) entomological surveillance is successfully used as an early detection warning, this method in central Italy seems ineffective. To achieve a high level of sensitivity, the entomological trapping effort should probably exceed a reasonable balance between cost and performance. Besides, WNV/USUV early detection can be addressed by horses and birds. Further research is needed to adapt the surveillance components in different epidemiological contexts.

Development of multiplex real-time PCR assays for differential detection of capripoxvirus, parapoxvirus and foot-and-mouth disease virus

This study reports the development of multiplex real-time PCR assays for differential detection of capripoxvirus (CaPV), parapoxvirus (PaPV) and foot-and-mouth disease virus (FMDV) in sheep, goats and cattle. Three multiplex assays were developed, a capripox (CaP) rule-out assay for simultaneous detection and differentiation of CaPV and PaPV, a FMD rule-out assay for simultaneous detection and differentiation of FMDV and PaPV, and a FMD/CaP rule-out assay for simultaneous detection and differentiation of CaPV, PaPV and FMDV. All multiplex assays included β-actin gene ACTB as an internal positive control to monitor PCR inhibition and accuracy of nucleic acid extractions. The optimized assays were highly specific to the target viruses (CaPV, PaPV and FMDV) with no cross-reactivity against other viruses that cause similar clinical signs. Using positive control plasmids as template, the limit of detection (LOD) of the multiplex assays were estimated as 2 CaPV, 7 PaPV and 15 FMDV copies per assay. The amplification efficiency (AE) and correlation coefficient (R² ), estimated from the standard curves (Ct vs. log₁₀ template dilution), were 94%-106% and >0.99, respectively, for CaP and FMD rule-out assays, 96%-116% (AE) and >0.98 (R² ), respectively, for CaP/FMD rule-out assays and 91%-102% and >0.99, respectively, for the corresponding singleplex assays. The diagnostic sensitivity (DSe) of the multiplex assays was assessed on 35 CaPV and 39 FMDV clinical specimens from experimentally infected (CS-E) animals, and 29 CaPV (LSDV), 28 FMDV and 36 PaPV clinical specimens from naturally infected (CS-N) animals; all tested positive (DSe 100%) except two CS-E FMDV specimens that were tested negative by FMD rule-out and the corresponding singleplex (FMDV) assays (37/39; DSe 95%). The newly developed multiplex assays offer a valuable tool for differential detection of clinically indistinguishable CaPV, PaPV and FMDV in suspected animals and animals with mixed infections.

West Nile and Usutu virus infections in wild birds admitted to rehabilitation centres in Extremadura, western Spain, 2017-2019

West Nile virus (WNV) is an emerging flavivirus transmitted generally by mosquitoes of Culex genus. It is maintained in an enzootic life cycle where birds act as reservoir hosts. Humans and horses are also susceptible to infection, and occasionally, they suffer from neurological complications. However, they do not transmit the virus to other vectors, behaving as dead-end hosts. Sporadic WNV outbreaks observed in horses and wild birds from Extremadura (western Spain) during 2016 and 2017 seasons prompted to carry out this survey in wild birds, focused on specimens coming from two wildlife rehabilitation centres. Between October 2017 and December 2019, samples from 391 wild birds, belonging to 56 different species were collected and analysed in search of evidence of WNV infection. The analysis of serum samples for WNV-specific antibodies by ELISA, whose specificity was subsequently confirmed by virus-neutralisation test (VNT) showed positive results in 18.23 % birds belonging to 18 different species. Pelecaniformes (33.33 %), Accipitriformes (25.77 %) and Strigiformes (22.92 %) orders had the higher seroprevalences. Remarkably, WNV-specific antibodies were found in a black stork for the first time in Europe. Analysis by real time RT-PCR in symptomatic birds confirmed the presence of WNV lineage 1 RNA in griffon vulture and little owls. Specificity analysis of ELISA positive and doubtful sera was performed by differential VNT titration against WNV and two other cross-reacting avian flaviviruses found in Spain: Usutu virus (USUV) and Bagaza virus (BAGV). Only four samples showed USUV-specific antibodies (1.04 %) corresponding to three species: Eurasian eagle-owl, griffon vulture and great bustard (first detection in Europe) whereas no samples were found reactive to BAGV. Differential VNT yielded undetermined flavivirus result in 16 samples (4.17 %). This is the first study carried out on wild birds from Extremadura (western Spain). It highlights the widespread circulation of WNV in the region and its co-circulation with USUV.

VectorDisk: A Microfluidic Platform Integrating Diagnostic Markers for Evidence-Based Mosquito Control

Effective mosquito monitoring relies on the accurate identification and characterization of the target population. Since this process requires specialist knowledge and equipment that is not widely available, automated field-deployable systems are highly desirable. We present a centrifugal microfluidic cartridge, the VectorDisk, which integrates TaqMan PCR assays in two feasibility studies, aiming to assess multiplexing capability, specificity, and reproducibility in detecting disk-integrated vector-related assays. In the first study, pools of 10 mosquitoes were used as samples. We tested 18 disks with 27 DNA and RNA assays each, using a combination of multiple microfluidic chambers and detection wavelengths (geometric and color multiplexing) to identify mosquito and malaria parasite species as well as insecticide resistance mechanisms. In the second study, purified nucleic acids served as samples to test arboviral and malaria infective mosquito assays. Nine disks were tested with 14 assays each. No false positive results were detected on any of the disks. The coefficient of variation in reproducibility tests was <10%. The modular nature of the platform, the easy adaptation of the primer/probe panels, the cold chain independence, the rapid (2–3 h) analysis, and the assay multiplexing capacity are key features, rendering the VectorDisk a potential candidate for automated vector analysis.

Evaluation of West Nile Virus Diagnostic Capacities in Veterinary Laboratories of the Mediterranean and Black Sea Regions

The increasing incidence of West Nile virus (WNV) in the Euro-Mediterranean area warrants the implementation of effective surveillance programs in animals. A crucial step in the fight against the disease is the evaluation of the capacity of the veterinary labs to accurately detect the infection in animal populations. In this context, the animal virology network of the MediLabSecure project organized an external quality assessment (EQA) to evaluate the WNV molecular and serological diagnostic capacities of beneficiary veterinary labs. Laboratories from 17 Mediterranean and Black Sea countries participated. The results of the triplex real time RT-PCR for simultaneous detection and differentiation of WNV lineage 1 (L1), lineage 2 (L2) and Usutu virus (USUV) were highly satisfactory, especially for L1 and L2, with detection rates of 97.9% and 100%, respectively. For USUV, 75% of the labs reported correct results. More limitations were observed for the generic detection of flaviviruses using conventional reverse-transcription polymerase chain reaction (RT-PCR), since only 46.1% reported correct results in the whole panel. As regards the serological panel, the results were excellent for the generic detection of WNV antibodies. More variability was observed for the specific detection of IgM antibodies with a higher percentage of incorrect results mainly in samples with low titers. This EQA provides a good overview of the WNV (and USUV) diagnostic performance of the involved veterinary labs and demonstrates that the implemented training program was successful in upgrading their diagnostic capacities.

Polymerase Spiral Reaction Assay for Rapid and Real Time Detection of West Nile Virus From Clinical Samples

West Nile virus (WNV) is a mosquito-borne virus of public health importance. Currently, there is no FDA approved vaccine available against WNV infection in humans. Therefore, the early diagnosis of the WNV infection is important for epidemiologic control and timely clinical management in areas where multiple Flaviviruses are endemic. The present study aimed to develop reverse transcription polymerase spiral reaction (RT-PSR) assay that rapidly and accurately detects the envelope (env) gene of WNV. RT-PSR assay was optimized at 63°C for 60 min using real-time turbidimeter or visual detection by the addition of SYBR Green I dye. The standard curve for RT-PSR assay was generated using the 10-fold serial dilutions of in vitro transcribed WNV RNA. To determine the detection limit of RT-PSR assay, an amplified product of conventional RT-PCR was in vitro transcribed as per standard protocol. The detection limit of the newly developed RT-PSR assay was compared with that of conventional RT-PCR and CDC reported TaqMan real-time RT-PCR using a serial 10-fold dilution of IVT WNV RNA. The detection limit of RT-PSR was found to be 1 RNA copy, which is 100-fold higher than that of conventional RT-PCR (100 copies). This suggests that RT-PSR assay is a valuable diagnostic tool for rapid and real-time detection of WNV in acute-phase serum samples. The assay was validated with a panel of 107 WNV suspected human clinical samples with signs of acute posterior uveitis and onset of febrile illness. Out of 107 samples, 30 were found positive by RT-PSR assay. The specificities of the selected primer sets were established by the absence of cross-reactivity with other closely related members viruses of the Flaviviruses, Alphaviruses, and Morbilliviruses groups. No cross-reactivity was observed with other viruses. To best of our knowledge, this is the first report describing the RT-PSR assay for the detection of RNA virus (WNV) in clinical samples. RT-PSR is a high throughput method and more than 30 reactions can be run at once in real-time turbidimeter. PSR assay has potential to be used for a rapid screening of large number of clinical samples in endemic areas during an outbreak.

Serological evidence of co-circulation of West Nile and Usutu viruses in equids from western Spain

West Nile virus (WNV) is a mosquito-borne emerging virus in Europe with capacity to cause neurological complications such as encephalitis or meningoencephalitis in humans, birds or equids. In Spain, WNV is actively circulating in mosquitoes, birds and horses in different regions, but never has been deeply studied in Extremadura. Therefore, the aim of this study was to evaluate the seroprevalence of WNV in equids of those areas and to analyse the risk factors associated with exposure to the virus. A total of 199 out of 725 equids presented antibodies against WNV by competition ELISA (27.45%), while 22 were doubtful (3.03%). Anti-WNV IgM antibodies were detected in 16 equids (2.21%), and 3 animals were doubtful (0.41%). All ELISA-reactive positive/doubtful sera (N = 226) were further tested by micro-virus neutralization test (VNT), and a total of 143 horses were confirmed as positive for WNV, obtaining a seroprevalence of 19.72% in equids of western Spain. In addition, specific antibodies against USUV were confirmed in 11 equids. In 24 equids, a specific flavivirus species (detected by ELISA test) could not be determined. The generalized linear mixed-effects models showed that the significant risk factors associated with individual WNV infection in equids were the age (adults) and hair coat colour (light), whereas in USUV infections, it was the breed (pure). Data demonstrated that WNV and USUV are circulating in regions of western Spain. Given the high WNV seroprevalence found in equids from the studied areas, it is important to improve the surveillance programmes of public health to detect undiagnosed human cases and to establish a vaccination programme in equid herds in these regions.

Toscana, West Nile, Usutu and tick-borne encephalitis viruses: external quality assessment for molecular detection of emerging neurotropic viruses in Europe, 2017

BackgroundNeurotropic arboviruses are increasingly recognised as causative agents of neurological disease in Europe but underdiagnosis is still suspected. Capability for accurate diagnosis is a prerequisite for adequate clinical and public health response.AimTo improve diagnostic capability in EVD-LabNet laboratories, we organised an external quality assessment (EQA) focusing on molecular detection of Toscana (TOSV), Usutu (USUV), West Nile (WNV) and tick-borne encephalitis viruses (TBEV).MethodsSixty-nine laboratories were invited. The EQA panel included two WNV RNA-positive samples (lineages 1 and 2), two TOSV RNA-positive samples (lineages A and B), one TBEV RNA-positive sample (Western subtype), one USUV RNA-positive sample and four negative samples. The EQA focused on overall capability rather than sensitivity of the used techniques. Only detection of one, clinically relevant, concentration per virus species and lineage was assessed.ResultsThe final EQA analysis included 51 laboratories from 35 countries; 44 of these laboratories were from 28 of 31 countries in the European Union/European Economic Area (EU/EEA). USUV diagnostic capability was lowest (28 laboratories in 18 countries), WNV detection capacity was highest (48 laboratories in 32 countries). Twenty-five laboratories were able to test the whole EQA panel, of which only 11 provided completely correct results. The highest scores were observed for WNV and TOSV (92%), followed by TBEV (86%) and USUV (75%).ConclusionWe observed wide variety in extraction methods and RT-PCR tests, showing a profound absence of standardisation across European laboratories. Overall, the results were not satisfactory; capacity and capability need to be improved in 40 laboratories.

Detection of Astrovirus in a Cow with Neurological Signs by Nanopore Technology, Italy

In this study, starting from nucleic acids purified from the brain tissue, Nanopore technology was used to identify the etiological agent of severe neurological signs observed in a cow which was immediately slaughtered. Histological examination revealed acute non-suppurative encephalomyelitis affecting the brainstem, cerebrum, cerebellum, and medulla oblongata, while by using PCR-based assays, the nucleic acids of major agents for neurological signs were not detected. By using Nanopore technology, 151 sequence reads were assigned to Bovine Astrovirus (BoAstV). Real-time RT-PCR and in situ hybridization (ISH) confirmed the presence of viral RNA in the brain. Moreover, using the combination of fluorescent ISH and immunofluorescence (IF) techniques, it was possible to detect BoAstV RNA and antigens in the same cells, suggesting the active replication of the virus in infected neurons. The nearly whole genome of the occurring strain (BoAstV PE3373/2019/Italy), obtained by Illumina NextSeq 500, showed the highest nucleotide sequence identity (94.11%) with BoAstV CH13/NeuroS1 26,730 strain, an encephalitis-associated bovine astrovirus. Here, we provide further evidence of the role of AstV as a neurotropic agent. Considering that in a high proportion of non-suppurative encephalitis cases, which are mostly indicative of a viral infection, the etiologic agent remains unknown, our result underscores the value and versatility of Nanopore technology for a rapid diagnosis when the PCR-based algorithm gives negative results.

Enhanced West Nile Virus Circulation in the Emilia-Romagna and Lombardy Regions (Northern Italy) in 2018 Detected by Entomological Surveillance

With several human cases reported annually since 2008 and the unapparent risk of infection of blood donors, the West Nile virus (WNV) is emerging as an important health issue in Europe. Italy, as well as other European countries, experienced a recrudescence of the virus circulation in 2018, which led to an increased number of human cases. An integrated surveillance plan was activated in the Emilia-Romagna and Lombardy regions (Northern Italy) since 2008 in order to monitor the intensity and timing of WNV circulation. A fundamental part of this plan consists in entomological surveillance. In 2018, the surveillance plan made it possible to collect 385,293 mosquitoes in 163 stations in the two Regions. In total 269,147 Culex mosquitoes were grouped into 2,337 pools and tested for WNV, which was detected in 232 pools. Circulation started in the central part of the Emilia-Romagna region in the middle of June, about one month before the previous seasons. Circulation suddenly expanded to the rest of the region and reached the Lombardy region in the middle of July. WNV circulated more intensively in the eastern part of the surveyed area, as confirmed by the highest number of human cases. A relationship between the number of mosquitoes collected and the virus incidence emerged, but the data obtained highlighted that the probability of detecting the virus in a given site was less than expected with a higher number of collected mosquitoes. A significant relationship was observed between the temperature recorded one week before the sampling and the number of collected mosquitoes, as well as between the estimated number of WNV-positive mosquitoes and the temperature recorded two weeks before the sampling. The two weeks delay in the influence of temperature on the positive mosquitoes is in line with the time of the virus extrinsic incubation in the mosquito. This finding confirms that temperature is one of the principal drivers in WNV mosquito infection. The surveillance system demonstrated the ability to detect the virus circulation early, particularly in areas where circulation was more intense. This allowed evaluating the effect of mosquito abundance and weather factors on virus circulation.

A Duplex Quantitative Real-Time Reverse Transcription-PCR for Simultaneous Detection and Differentiation of Flaviviruses of the Japanese Encephalitis and Ntaya Serocomplexes in Birds

High impact, mosquito-borne flaviviruses such as West Nile virus (WNV), Usutu virus (USUV), Japanese encephalitis virus (JEV), Tembusu virus (TMUV), and Bagaza/Israel turkey meningoencephalomyelitis virus (BAGV/ITV) are emerging in different areas of the world. These viruses belong to the Japanese encephalitis (JE) serocomplex (JEV, WNV, and USUV) and the Ntaya serocomplex (TMUV and BAGV/ITV). Notably, they share transmission route (mosquito bite) and reservoir host type (wild birds), and some of them co-circulate in the same areas, infecting overlapping mosquito and avian population. This may simplify epidemiological surveillance, since it allows the detection of different infections targeting the same population, but also represents a challenge, as the diagnostic tools applied need to detect the whole range of flaviviruses surveyed, and correctly differentiate between these closely related pathogens. To this aim, a duplex real-time RT-PCR (dRRT-PCR) method has been developed for the simultaneous and differential detection of JE and Ntaya flavivirus serocomplexes. The method has been standardized and evaluated by analyzing a panel of 49 flaviviral and non-flaviviral isolates, and clinical samples of different bird species obtained from experimental infections or from the field, proving its value for virus detection in apparently healthy or suspicious animals. This new dRRT-PCR technique is a reliable, specific and highly sensitive tool for rapid detection and differentiation of JE and Ntaya flavivirus groups in either domestic or wild animals. This novel method can be implemented in animal virology diagnostic laboratories as screening tool in routine surveillance and in the event of bird encephalitis emergence.

Population dynamics, pathogen detection and insecticide resistance of mosquito and sand fly in refugee camps, Greece

BACKGROUND

As of 2015 thousands of refugees are being hosted in temporary refugee camps in Greece. Displaced populations, travelling and living under poor conditions with limited access to healthcare are at a high risk of exposure to vector borne disease (VBD). This study sought to evaluate the risk for VBD transmission within refugee camps in Greece by analyzing the mosquito and sand fly populations present, in light of designing effective and efficient context specific vector and disease control programs.

METHODS

A vector/pathogen surveillance network targeting mosquitoes and sand flies was deployed in four temporary refugee camps in Greece. Sample collections were conducted bi-weekly during June-September 2017 with the use of Centers for Disease Control (CDC) light traps and oviposition traps. Using conventional and molecular diagnostic tools we investigated the mosquito/sand fly species composition, population dynamics, pathogen infection rates, and insecticide resistance status in the major vector species.

RESULTS

Important disease vectors including Anopheles sacharovi, Culex pipiens, Aedes albopictus and the Leishmania vectors Phlebotomus neglectus, P. perfiliewi and P. tobbi were recorded in the study refugee camps. No mosquito pathogens (Plasmodium parasites, flaviviruses) were detected in the analysed samples yet high sand fly Leishmania infection rates are reported. Culex pipiens mosquitoes displayed relatively high knock down resistance (kdr) mutation allelic frequencies (ranging from 41.0 to 63.3%) while kdr mutations were also detected in Ae. albopictus populations, but not in Anopheles and sand fly specimens. No diflubenzuron (DFB) mutations were detected in any of the mosquito species analysed.

CONCLUSIONS

Important disease vectors and pathogens in vectors (Leishmania spp.) were recorded in the refugee camps indicating a situational risk factor for disease transmission. The Cx. pipiens and Ae. albopictus kdr mutation frequencies recorded pose a potential threat against the effectiveness of pyrethroid insecticides in these settings. In contrast, pyrethroids appear suitable for the control of Anopheles mosquitoes and sand flies and DFB for Cx. pipiens and Ae. albopictus larvicide applications. Targeted actions ensuring adequate living conditions and the establishment of integrated vector-borne disease surveillance programs in refugee settlements are essential for protecting refugee populations against VBDs.

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.

Assessing the role of migratory birds in the introduction of ticks and tick-borne pathogens from African countries: An Italian experience

The continuous flow of billions of birds between Africa and Europe creates an "ecological bridge" between physically remote areas. Migratory birds fly south from their breeding grounds during late summer/fall and fly back in spring. These movements regulate the spread of internal and external parasites, as well as pathogens of potential public health concern. The aim of the present study was to investigate the possible introduction of exotic tick species and tick-borne pathogens into Europe via migratory birds. At the bird observatory of Ventotene island (Italy), 443 feeding ticks were collected from 249 birds captured and ringed during their northbound migration in spring 2013. Each tick was identified by morphological and molecular methods and then tested for bacterial and viral pathogens: Borrelia burgdorferi s.l., Rickettsia spp., Ehrlichia ruminantium and Coxiella burnetii, Crimean Congo haemorrhagic fever virus (CCHFV) and Flavivirus. Morphological and molecular identification confirmed Hyalomma rufipes as the most abundant species among the collected arthropods (366/443; 82.6%) followed by Hyalomma marginatum (10/433; 2.3%). Rickettsia aeschlimannii was identified in 158 ticks, while one engorged Amblyomma variegatum nymph was infected with Rickettsia africae. The other bacteria were not detected in any specimen. Among viruses, RNA belonging to West Nile virus and other Flavivirus were detected whereas all ticks were negative for CCHFV RNA. These results confirm how migratory birds play a role in carrying Rickettsia-infected ticks, as well as viruses of zoonotic importance, from Africa into Europe. To what extent tick species are capable of establishing a permanent population once introduced in naïve areas, is far from defined and deserve further investigation.

Usutu Virus: An Arbovirus on the Rise

The Usutu virus (USUV) is a flavivirus that is drawing increasing attention because of its potential for emergence. First isolated in Africa, it was introduced into Europe where it caused significant outbreaks in birds, such as in Austria in 2001. Since then, its geographical distribution has rapidly expanded, with increased circulation, especially in the last few years. Similar to West Nile virus (WNV), the USUV enzootic transmission cycle involves Culex mosquitoes as vectors, and birds as amplifying reservoir hosts, with humans and other mammals likely being dead-end hosts. A similarity in the ecology of these two viruses, which co-circulate in several European countries, highlights USUV’s potential to become an important human pathogen. While USUV has had a severe impact on the blackbird population, the number of human cases remains low, with most infections being asymptomatic. However, some rare cases of neurological disease have been described, both in healthy and immuno-compromised patients. Here, we will discuss the transmission dynamics and the current state of USUV circulation in Europe.

Influence of flavivirus co-circulation in serological diagnostics and surveillance: A model of study using West Nile, Usutu and Bagaza viruses

This study aims at assessing the serological cross-reactions existing between three mosquito-borne flaviviruses with avian reservoirs co-circulating in Europe: West Nile (WNV), Usutu (USUV) and Bagaza (BAGV). The study is useful for a better interpretation of serological results in diagnostics and surveillance. Serum samples obtained from a natural host, the red-legged partridge (Alectoris rufa), experimentally infected with WNV, USUV or BAGV were analysed using two commercially available WNV competition ELISAs suitable for serological surveillance, and by the confirmatory virus neutralization test (VNT). The ELISAs examined showed different levels of specificity for WNV, as judged by cross-reaction observed with the other flaviviruses. By VNT, virus-specific antibodies were confirmed in 80%, 50% or 0% of sera from WNV-, BAGV-, or USUV-inoculated birds, respectively. The results indicate how the co-circulation of cross-reacting flaviviruses may affect the outcomes of WNV serological surveillance when applying currently available serological tools. On the one hand, the choice of the ELISA test for antibody screening should consider the differences found in specificity, since one test is more specific for WNV while the other one is more suitable for detection of a broader range of flavivirus antibodies. On the other hand, besides corroborating that cross-neutralization occurs between flaviviruses from different serocomplexes (WNV/USUV and BAGV), this study points out that cross-neutralization between WNV and USUV is not symmetric, and reveals the difficulty to identify USUV infections serologically. This finding indicates that actual USUV infections might be underestimated in the current diagnostic schemes.

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.