Magpies as hosts for West Nile virus, southern France

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.

Understanding West Nile virus transmission: Mathematical modelling to quantify the most critical parameters to predict infection dynamics

West Nile disease is a vector-borne disease caused by West Nile virus (WNV), involving mosquitoes as vectors and birds as maintenance hosts. Humans and other mammals can be infected via mosquito bites, developing symptoms ranging from mild fever to severe neurological infection. Due to the worldwide spread of WNV, human infection risk is high in several countries. Nevertheless, there are still several knowledge gaps regarding WNV dynamics. Several aspects of transmission taking place between birds and mosquitoes, such as the length of the infectious period in birds or mosquito biting rates, are still not fully understood, and precise quantitative estimates are still lacking for the European species involved. This lack of knowledge affects the precision of parameter values when modelling the infection, consequently resulting in a potential impairment of the reliability of model simulations and predictions and in a lack of the overall understanding of WNV spread. Further investigations are thus needed to better understand these aspects, but field studies, especially those involving several wild species, such as in the case of WNV, can be challenging. Thus, it becomes crucial to identify which transmission processes most influence the dynamics of WNV. In the present work, we propose a sensitivity analysis to investigate which of the selected epidemiological parameters of WNV have the largest impact on the spread of the infection. Based on a mathematical model simulating WNV spread into the Lombardy region (northern Italy), the basic reproduction number of the infection was estimated and used to quantify infection spread into mosquitoes and birds. Then, we quantified how variations in four epidemiological parameters representing the duration of the infectious period in birds, the mosquito biting rate on birds, and the competence and susceptibility to infection of different bird species might affect WNV transmission. Our study highlights that knowledge gaps in WNV epidemiology affect the precision in several parameters. Although all investigated parameters affected the spread of WNV and the modelling precision, the duration of the infectious period in birds and mosquito biting rate are the most impactful, pointing out the need of focusing future studies on a better estimate of these parameters at first. In addition, our study suggests that a WNV outbreak is very likely to occur in all areas with suitable temperatures, highlighting the wide area where WNV represents a serious risk for public health.

A One Health view of the West Nile virus outbreak in Andalusia (Spain) in 2020

Reports of West Nile virus (WNV) associated disease in humans were scarce in Spain until summer 2020, when 77 cases were reported, eight fatal. Most cases occurred next to the Guadalquivir River in the Sevillian villages of Puebla del Río and Coria del Río. Detection of WNV disease in humans was preceded by a large increase in the abundance of Culex perexiguus in the neighbourhood of the villages where most human cases occurred. The first WNV infected mosquitoes were captured approximately one month before the detection of the first human cases. Overall, 33 positive pools of Cx. perexiguus and one pool of Culex pipiens were found. Serology of wild birds confirmed WNV circulation inside the affected villages, that transmission to humans also occurred in urban settings and suggests that virus circulation was geographically more widespread than disease cases in humans or horses may indicate. A high prevalence of antibodies was detected in blackbirds (Turdus merula) suggesting that this species played an important role in the amplification of WNV in urban areas. Culex perexiguus was the main vector of WNV among birds in natural and agricultural areas, while its role in urban areas needs to be investigated in more detail. Culex pipiens may have played some role as bridge vector of WNV between birds and humans once the enzootic transmission cycle driven by Cx. perexiguus occurred inside the villages. Surveillance of virus in mosquitoes has the potential to detect WNV well in advance of the first human cases.

Exposure of Wild Ungulates to the Usutu and Tick-Borne Encephalitis Viruses in France in 2009-2014: Evidence of Undetected Flavivirus Circulation a Decade Ago

Abstract: Flaviviruses have become increasingly important pathogens in Europe over the past few decades. A better understanding of the spatiotemporal distribution of flaviviruses in France is needed to better define risk areas and to gain knowledge of the dynamics of virus transmission cycles. Serum samples from 1014 wild boar and 758 roe deer from 16 departments (administrative units) in France collected from 2009 to 2014 were screened for flavivirus antibodies using a competitive ELISA (cELISA) technique. Serum samples found to be positive or doubtful by cELISA were then tested for antibodies directed against West Nile virus (WNV), Usutu virus (USUV), Bagaza virus (BAGV), and tick-borne encephalitis/Louping ill viruses (TBEV/LIV) by microsphere immunoassays (except BAGV) and micro-neutralization tests. USUV antibodies were detected only in southeastern and southwestern areas. TBEV/LIV antibodies were detected in serum samples from eastern, southwestern and northern departments. The results indicate continuous circulation of USUV in southern France from 2009 to 2014, which was unnoticed by the French monitoring system for bird mortality. The findings also confirm wider distribution of TBEV in the eastern part of the country than of human clinical cases. However, further studies are needed to determine the tick-borne flavivirus responsible for the seroconversion in southwestern and northern France.

Usefulness of Eurasian Magpies (Pica pica) for West Nile virus Surveillance in Non-Endemic and Endemic Situations

: In September 2017, passive surveillance allowed the detection of West Nile virus (WNV) lineage 2 for the first time in northern Spain in a northern goshawk (Accipiter gentilis). However, a cross sectional study carried out in Eurasian magpies (Pica pica) in a nearby area evidenced that WNV had been circulating two months earlier. Therefore, active surveillance in Eurasian magpies proved its effectiveness for the early detection of WNV in a non-endemic area. Further surveys in 2018 and the beginning of 2019 using young magpies (i.e., born after 2017) showed the repeated circulation of WNV in the same region in the following transmission season. Therefore, active surveillance in Eurasian magpies as well proved to be useful for the detection of WNV circulation in areas that may be considered as endemic. In this manuscript we present the results of those studies and discuss reasons that make the Eurasian magpies an ideal species for the surveillance of WNV, both in endemic and non-endemic areas.

West Nile virus in Algeria: a comprehensive overview

West Nile virus (WNV) is a mosquito-borne virus belonging to the genus Flavivirus, related to the Japanese encephalitis antigenic complex of Flaviviridae family. It is transmitted by the bite of infected mosquitoes. The virus is maintained in a mosquito-bird-mosquito transmission cycle. WNV has recently dramatically expanded its geographical range and is now considered the most widespread arbovirus in the world, including the Americas, Europe and countries facing the Mediterranean Basin. In Algeria, West Nile disease (WND) infections with human meningoencephalitis cases have been reported in 1994 in Tinerkouk (southwest Sahara. In autumn 2012, one fatal clinical case of WNV neuroinvasive infection was reported in Jijel (coastal east). During the same year, a retrospective serosurvey performed in Algiers and bordering areas highlighted specific anti-WNV IgG in local population. Between 2013 and 2014 two clinical cases were reported, in Timimoune (south) and Guelma (northeast) respectively. Although no case was reported in equids, serosurveys demonstrated its presence: an animal serosurvey was conducted in Djanet (south) in 1975, and in 2014 a seroprevalence of equids in the northeast part of Algeria highlighted a virus circulation. This review aims to evaluate the global epidemiologic situation of West Nile disease in Algeria, with an updated situation based on human cases, equine reports and entomologic investigations. Our study reinforces the need for building the capacity for surveillance in this region to prevent future emergence of WNV and other arboviruses.

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.

An Integrative Eco-Epidemiological Analysis of West Nile Virus Transmission

West Nile disease, caused by the West Nile virus (WNV), is a mosquito-borne zoonotic disease affecting humans and horses that involves wild birds as amplifying hosts. The mechanisms of WNV transmission remain unclear in Europe where the occurrence of outbreaks has dramatically increased in recent years. We used a dataset on the competence, distribution, abundance, diversity and dispersal of wild bird hosts and mosquito vectors to test alternative hypotheses concerning the transmission of WNV in Southern France. We modelled the successive processes of introduction, amplification, dispersal and spillover of WNV to incidental hosts based on host-vector contact rates on various land cover types and over four seasons. We evaluated the relative importance of the mechanisms tested using two independent serological datasets of WNV antibodies collected in wild birds and horses. We found that the same transmission processes (seasonal virus introduction by migratory birds, Culex modestus mosquitoes as amplifying vectors, heterogeneity in avian host competence, absence of 'dilution effect') best explain the spatial variations in WNV seroprevalence in the two serological datasets. Our results provide new insights on the pathways of WNV introduction, amplification and spillover and the contribution of bird and mosquito species to WNV transmission in Southern France.

Accuracy estimation of an indirect ELISA for the detection of West Nile Virus antibodies in wild birds using a latent class model

West Nile virus (WNV) and Usutu virus (USUV), genus Flavivirus, are members of the Japanese encephalitis virus antigenic complex, and are maintained primarily in an enzootic cycle between mosquitoes and birds. WNV is zoonotic, and poses a threat to public health, especially in relation to blood transfusion. Serosurveillance of wild birds is suitable for early detection of WNV circulation, although concerns remain to be addressed as regards i) the type of test used, whether ELISA, virus neutralization test (VNT), plaque reduction neutralization test (PRNT), ii) the reagents (antigens, revealing antibodies), iii) the different bird species involved, and iv) potential cross-reactions with other Flaviviruses, such as USUV. The authors developed an indirect IgG ELISA with pan-avian specificity using EDIII protein as antigen and a monoclonal antibody (mAb 1A3) with broad reactivity for avian IgG. A total of 140 serum samples were collected from juvenile European magpies (Pica pica) in areas where both WNV and USUV were co-circulating. The samples were then tested using this in-house ELISA and VNT in parallel. Estimation of test accuracy was performed using different Bayesian two latent class models. At a cut-off set at an optical density percentage (OD%) of 15, the ELISA showed a posterior median of diagnostic sensitivity (DSe) of 88% (95%PCI: 73-99%) and a diagnostic specificity (DSp) of 86% (95%PCI: 68-99%). At this cut-off, ELISA and VNT (cut-off 1/10) performances were comparable: DSe=91% (95%PCI: 79-99%), and DSp=77% (95%PCI: 59-98%). With the cut-off increased to 30 OD%, the ELISA DSe dropped to 78% (95%PCI: 52-99%), and the DSp rose to 94% (95%PCI: 83-100%). In field conditions, the cut-off that yields the best accuracy for the ELISA appears to correspond to 15 OD%. In areas where other Flaviviruses are circulating, however, it might be appropriate to raise the cut-off to 30 OD% in order to achieve higher specificity and reduce the detection of seropositive birds infected by other Flaviviruses, such as USUV.

Seroprevalence of West Nile virus antibodies in equids in the North-East of Algeria and detection of virus circulation in 2014

West Nile fever (WNF) is a viral disease of wild birds transmitted by mosquitoes. Humans and equids can also be affected and suffer from meningoencephalitis. In Algeria, since the 1994 epidemic, no data on WNV circulation was available until 2012. In September 2012, a fatal human case of WNV neuro-invasive infection occurred in Jijel province. This study describes the first seroprevalence study of West Nile virus (WNV) antibodies conducted in the equine population in Algeria. During 2014, serum samples were collected from 293 equids (222 donkeys and 71 horses) asymptomatic and unvaccinated for WNV in three localities in Northeastern wetlands of Algeria. Antibodies against WNV were found in 51 samples (seroprevalence 17.4%) of sampled equids, distributed as follows: 19 (seroprevalence 26.8%) horses and 32 (seroprevalence 14.4%) donkeys. Moreover 7 horses coming from Blida, in the center of Algeria, were tested before and after an 8-months stay in North-East Algeria. We observe a seroconversion in 2 horses, showing WNV circulation in 2014 in this specific region of Algeria.

Recent circulation of West Nile virus and potentially other closely related flaviviruses in Southern France

In recent years, the number of West Nile virus (WNV) cases reported in horses and humans has increased dramatically throughout the Mediterranean basin. Furthermore, the emergence of Usutu virus (USUV) in Austria in 2001, and its subsequent expansion to Hungary, Spain, Italy, Switzerland, the United Kingdom, and Germany, has given added cause for concern regarding the impact of the spread of flaviviruses on human and animal health in western Europe. Despite frequent detection of WNV and USUV cases in neighboring countries, no case of WNV has been detected in France since 2006 and USUV has never been reported. However, recent investigations focused on detecting the circulation of flaviviruses in France are lacking. We investigated the circulation of WNV and USUV viruses in wild birds in southern France on the basis of a serological survey conducted on a sentinel species, the magpie (Pica pica), in the Camargue area from November, 2009, to December, 2010. We detected WNV-neutralizing antibodies at a high titer (160) in a second-year bird showing recent exposure to WNV, although no WNV case has been detected in humans or in horses since 2004 in the Camargue. In addition, we observed low titers (10 or 20) of USUV-specific antibodies in six magpies, two of which were also seropositive for WNV. Such low titers do not give grounds for concluding that these birds had been exposed to USUV; cross-reactions at low titers may occur between antigenically closely related flaviviruses. But these results urge for further investigations into the circulation of flaviviruses in southern France. They also emphasize the necessity of undertaking epidemiological studies on a long-term basis, rather than over short periods following public health crises, to gain insight into viral dynamics within natural reservoirs.

Ecological surveillance for West Nile in Catalonia (Spain), learning from a five-year period of follow-up

To enhance early detection of West Nile virus (WNV) transmission, an integrated ecological surveillance system was implemented in Catalonia (north-eastern Spain) from 2007 to 2011. This system incorporated passive and active equine surveillance, periodical testing of chicken sentinels in wetland areas, serosurveillance wild birds and testing of adult mosquitoes. Samples from 298 equines, 100 sentinel chickens, 1086 wild birds and 39 599 mosquitoes were analysed. During these 5 years, no acute WNV infection was detected in humans or domestic animal populations in Catalonia. WNV was not detected in mosquitoes either. Nevertheless, several seroconversions in resident and migrant wild birds indicate that local WNV or other closely related flaviviruses transmission was occurring among bird populations. These data indicate that bird and mosquito surveillance can detect otherwise silent transmission of flaviviruses and give some insights regarding possible avian hosts and vectors in a European setting.

Risks of emerging infectious diseases: evolving threats in a changing area, the mediterranean basin

The Mediterranean basin is a biodiversity hotspot; it has historically had a large human presence that has shaped ecosystems for millennia. As the cradle of many civilizations, the area was one of the main theatres for transitions that punctuated both human and pathogen histories, which are intimately linked. Today we are living through another great historical transition summarized in the expression 'global changes'. In this context, we are witnessing a rise in the emergence of pathogens widely associated with aforementioned global changes. The Mediterranean basin might be especially vulnerable to this phenomenon due to the acute consequences global changes will have in this key intercontinental interface region. In addition, Arab revolutions and European economic crisis are creating both sanitary issues and presenting new opportunities to improve infectious disease control and prevention in the region. The aim of this review is to identify the impacts that ongoing changes might have on the risk of infectious disease emergence in the Mediterranean basin. We focussed on three key domains undergoing transformations: (i) resources, namely safe drinking water and animal products, (ii) socio-economic factors including health inequalities within countries and poor sanitary conditions linked to ongoing conflicts and (iii) movements of people and goods that are reshaped by current changes and are intimately linked to the risk of disease proliferation. Building on recent examples, we try to identify upcoming challenges and discuss ways to meet them in the light of existing international human and veterinary health guidelines and their possible improvements.

Pathology and immunohistochemical findings of west nile virus infection in psittaciformes

West Nile virus (WNV) infection was diagnosed in 38 psittacine birds based on histology, immunohistochemistry, and reverse transcriptase polymerase chain reaction (RT-PCR). Rosellas (Platycercus spp, n = 13), conures (Enicognathus, Aratinga, and Nandayus spp, n = 6), and lorikeets (Trichoglossus spp, n = 6) represented the most commonly affected species. Clinical signs ranged from lethargy, ruffled feathers, anorexia, and weight loss in most birds to sudden death in others. Except for mild to moderate enlargement of liver and spleen, there were no significant gross lesions at necropsy. Histopathologic findings included lymphoplasmacytic and histiocytic hepatitis, interstitial nephritis, myocarditis, splenitis, enteritis, pancreatitis, and occasionally, encephalitis. Viral antigen was detected by immunohistochemistry in 34 of 35 hearts (97.1%), 29 of 32 pancreata (90.6%), 33 of 37 kidneys (89.2%), 31 of 35 intestines (88.6%), 27 of 33 gizzards (81.8%), 8 of 10 ovaries (80%), 27 of 34 spleens (79.4%), 30 of 38 livers (78.9%), 23 of 32 lungs (71.9%), 21 of 31 proventriculi (67.7%), 14 of 21 adrenals (66.7%), 10 of 16 testes (62.5%), 17 of 30 brains (56.7%), 15 of 27 skins (55.5%), 3 of 6 oviducts (50%), 15 of 34 skeletal muscles (44.1%), 11 of 27 crop or esophagus (40.7%), and 1 of 6 thymuses (16.7%). Kidney was positive for WNV by RT-PCR in all the cases tested. In conclusion, Psittaciformes are susceptible to West Nile virus infection, and WNV infections are often associated with nonspecific clinical signs and widespread viral distribution in this order of birds.

Low West Nile virus circulation in wild birds in an area of recurring outbreaks in Southern France

West Nile virus (WNV) has a history of irregular but recurrent epizootics in countries of Mediterranean and of Central and Eastern Europe. We have investigated the temporal enzootic activity of WNV in free-ranging birds over a 3-year period in an area with sporadic occurrences of WNV outbreaks in Southern France. We conducted an intensive serologic survey on several wild bird populations (>4000 serum samples collected from 3300 birds) selected as potential indicators of the WNV circulation. WNV antibodies were detected by seroneutralization and/or plaque reduction neutralization in house sparrows, black-billed magpies, and scops owls, but these species appeared to be insufficient indicators of WNV circulation. Overall seroprevalence was low (<1%), including in birds that had been potentially exposed to the virus during recent outbreaks. However, the detection of a seroconversion in one bird, as well as the detection of seropositive birds in all years of our monitoring, including juveniles, indicate a constant annual circulation of WNV at a low level, including in years without any detectable emergence of WN fever in horses or humans.

A metapopulation model to simulate West Nile virus circulation in Western Africa, Southern Europe and the Mediterranean basin

In Europe, virological and epidemiological data collected in wild birds and horses suggest that a recurrent circulation of West Nile virus (WNV) could exist in some areas. Whether this circulation is permanent (due to overwintering mechanisms) or not remains unknown. The current conception of WNV epidemiology suggests that it is not: this conception combines an enzootic WNV circulation in tropical Africa with seasonal introductions of the virus in Europe by migratory birds. The objectives of this work were to (i) model this conception of WNV global circulation; and (ii) evaluate whether the model could reproduce data and patterns observed in Europe and Africa in vectors, horses, and birds. The model was calibrated using published seroprevalence data obtained from African (Senegal) and European (Spain) wild birds, and validated using independent, published data: seroprevalence rates in migratory and resident wild birds, minimal infection rates in vectors, as well as seroprevalence and incidence rates in horses. According to this model, overwintering mechanisms are not needed to reproduce the observed data. However, the existence of such mechanisms cannot be ruled out.