West Nile Virus Seroprevalence Research Articles

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

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

Seroprevalence of West Nile Virus in Tampa Bay Florida Patients Admitted to Hospital during 2020-2021 for Respiratory Symptoms.

West Nile virus (WNV) is an arbovirus spread primarily by Culex mosquitoes, with humans being a dead-end host. WNV was introduced to Florida in 2001, with 467 confirmed cases since. It is estimated that 80 percent of cases are asymptomatic, with mild cases presenting as a non-specific flu-like illness. Currently, detection of WNV in humans occurs primarily in healthcare settings via RT-PCR or CSF IgM when patients present with severe manifestations of disease including fever, meningitis, encephalitis, or acute flaccid paralysis. Given the short window of detectable viremia and requirement for CSF sampling, most WNV infections never receive an official diagnosis. This study utilized enzyme-linked immunosorbent assay (ELISA) to detect WNV IgG antibodies in 250 patient serum and plasma samples collected at Tampa General Hospital during 2020 and 2021. Plaque reduction neutralization tests were used to confirm ELISA results. Out of the 250 patients included in this study, 18.8% of them were IgG positive, consistent with previous WNV exposure. There was no relationship between WNV exposure and age or sex.

West Nile Virus Sero-Reactive Animals Reveal Potential Zoonotic Threat In Nigeria

West Nile Virus (WNV) is a zoonotic mosquito borne arbovirus that causes encephalitis in horses and human. It is a pathogen of public health importance globally. Data on WNV epizootics in Nigeria is limited, necessitating seroprevalence studies in animals. In this study, 118 sera from Polo horses and 66 archival sera from 31 horses, 10 chicken, 15 rabbits and 10 dogs in Northern and South-Western Nigeria were screened for WNV using West Nile multi-species competitive ELISA. The overall seroprevalence of WNV was 78.26% (n=144). In horses, 93.28% (n=139) of the 149 horse sera were positive, all the 10 chicken samples tested were negative to WNV, only 1 (6.67%) of the 15 rabbits sera tested positive and 4(40%) of 10 dog sera tested was positive. The lack of sero-reactivity in domestic chickens in this study does not suggest a low incidence rate in wild birds that are known reservoirs. Sero-reactivity in rabbits and dogs indicates their exposure and susceptibility to WNV and therefore requires further investigation. The high sero-reactivity recorded in horses reiterates the important role they play in WNV epizootics which underscores the public health risk associated with WNV at the human-animal interface in Nigeria.

Serological survey reveals enzootic circulation of St. Louis encephalitis and West Nile viruses in semiarid Monte ecosystem of Argentina

St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) are arboviruses transmitted by Culex mosquitoes and amplified in avian hosts. The present study aimed to investigate the presence and seasonal circulation of SLEV and WNV in La Rioja province, within the semiarid ecoregion of the Monte, Argentina. Over a two-year period, avian sera were collected and tested for neutralizing antibodies against SLEV and WNV. Our results reveal the enzootic activity of both viruses in this challenging environment. SLEV seroprevalence was 4.5% (35/778), with higher activity in spring (2016) and autumn (2017). WNV seroprevalence was 3.5% (27/778), peaking during the summer 2016–2017. Greater seroprevalence for SLEV in 2016 was detected for the Lark-like Brushrunner (Coryphistera alaudina) and the Short-billed Canastero (Asthenes baeri) and in 2017 for the Black-crested Finch (Lophospingus pusillus) and Lark-like Brushrunner, whereas for WNV greater seroprevalence in 2016 was detected for the Picui Ground Dove (Columbina picui) and in 2017 for the Lark-like Brushrunner and Band-tailed Seedeater (Catamenia analis). Additionally, five avian individuals experienced seroconversion during the sampling period, namely the Lark-like Brushrunner and White-fronted Woodpecker (Melanerpes cactorum) for SLEV, and the Lark-like Brushrunner, Greater Wagtail Tyrant (Stigmatura budytoides) and Many-colored Chaco Finch (Saltatricula multicolor) for WNV. The study highlights the persistence and circulation of these viruses in a semiarid ecosystem, raising questions about overwintering mechanisms and transmission dynamics. This research contributes to understanding arbovirus ecology in diverse environments. Further investigations are needed to assess the specific mechanisms facilitating virus persistence in the Monte ecoregion.

A Retrospective Study on the Seroprevalence of West Nile Virus Among Donkeys and Mules in Bulgaria.

Background: West Nile virus (WNV) infection, caused by a flavivirus, emerged in Europe and America in the past two decades. The etiological agent causes asymptomatic to life-threatening infection in humans and in some animal species. The objective of this study was to evaluate the seroprevalence of WNV among donkeys and mules in Bulgaria. Methods: A total of 200 archived serum samples were tested by competitive enzyme-linked immunosorbent assay (ELISA). Positive samples were additionally analyzed by virus neutralization assay. Results: Seroprevalence of 7% (14/200) was established among tested animals by ELISA. Two samples were subsequently verified for the presence of virus neutralizing antibodies; thus, the seroprevalence against WNV was determined to be 1% (2/200 [confidence interval = 0.12-3.61]). Positive results among mules included in the study were not found. Conclusion: The findings in the present research demonstrate that donkeys are exposed to WNV infection and seroconvert, which adds to the understanding of virus circulation among donkeys in settlements in north and south Bulgaria.

First Serological Evidence of West Nile Virus among Individuals with Febrile Illness in a Tertiary Hospital in Port Harcourt, Nigeria

Aims: West Nile Virus (WNV) infection can cause severe illness. Very little is known about the seroepidemiology of WNV infection in individuals with febrile illness in Nigeria and many other developing countries. This study was carried out to determine the seroprevalence of WNV in individuals with febrile illness attending a tertiary hospital in Port Harcourt, Nigeria and to determine if there was an association between WNV infection with age and sex.&#x0D; Study Design: Cross-Sectional Study&#x0D; Place and Duration of Study: Port Harcourt in Rivers State, Nigeria from September 2019 to December 2019.&#x0D; Methods: Human sera were obtained and WNV IgG was determined using the Enzyme-Linked Immunosorbent Assay (ELISA) technique.&#x0D; Results: Of the 90 study subjects tested, WNV IgG antibodies were present in 27 (30.0%) study participants while 63 (70.0%) study participants were seronegative for WNV IgG antibody. With age, a higher prevalence of WNV occurred among 61-70-year-olds (31.3%, n= 5) compared to 41-60 (30.8%, n= 12) and 20-40 (28.6%, n= 10). A higher prevalence of WNV IgG antibodies occurred in males (34.3%, n=12) than their female counterparts (30.9%, n=17). This study indicated that there is no association between WNV infection with age and sex.&#x0D; Conclusion and Recommendations: These results show that WNV is circulating in Rivers State and has accounted for malaria-like infection in the region. It is recommended that WNV serological testing for malaria-infected individuals should be included as a routine test since they are most likely to present similar symptoms of WNV fever. Also, proper hygiene which includes eliminating mosquito breeding sites is recommended to mitigate the spread of West Nile Virus infection.

Long-term serological surveillance for West Nile and Usutu virus in horses in south-West Spain

West Nile virus (WNV) is a re-emerging zoonotic pathogen with increasing incidence in Europe, producing a recent outbreak in 2020 in Spain with 77 human cases and eight fatalities. However, the factors explaining the observed changes in the incidence of WNV in Europe are not completely understood. Longitudinal monitoring of WNV in wild animals across Europe is a useful approach to understand the eco-epidemiology of WNV in the wild and the risk of spillover into humans. However, such studies are very scarce up to now. Here, we analysed the occurrence of WNV and Usutu virus (USUV) antibodies in 2102 samples collected between 2005 and 2020 from a population of feral horses in Doñana National Park. The prevalence of WNV antibodies varied between years, with a mean seroprevalence of 8.1% (range 0%–25%) and seasonally. Climate conditions including mean minimum annual temperatures and mean rainy days per year were positively correlated with WNV seroprevalence, while the annual rainfall was negatively. We also detected the highest incidence of seroconversions in 2020 coinciding with the human outbreak in southern Spain. Usutu virus-specific antibodies were detected in the horse population since 2011. The WNV outbreak in humans was preceded by a long period of increasing circulation of WNV among horses with a very high exposure in the year of the outbreak. These results highlight the utility of One Health approaches to better understand the transmission dynamics of zoonotics pathogens.

An Investigation of West Nile Virus Infection in Local Wild Birds Species

The transmission of West Nile Virus (WNV) to new locations is mostly facilitated by migratory birds. Türkiye's domestic ducks, geese, and chickens have already tested positive for WNV by serology. This study was conducted to identify the seroprevalence of WNV in wild bird species because wild birds in the Western Mediterranean Region are found along migration routes from Africa to Europe, they are home to a wide variety of bird species due to the abundance of lakes and wetlands, the mild Mediterranean climate, and some areas that are suitable habitat for mosquitoes due to their low altitude. Serum samples were taken from 141 wild birds in Isparta (66), Burdur (42), and Antalya (33) for this study on birds in the wild. During serological studies, there was no evidence of WNV-specific antibodies.

Low Seroprevalence of WNV in Namibian Dogs Suggests a Limited Effectiveness as Sentinels for Infection Monitoring.

West Nile virus (WNV) is an important zoonotic Flavivirus responsible for mild fever to severe neurological disease in humans and horses. Despite the occurrence of major previous outbreaks in Namibia and the likelihood of the current endemicity of the virus, only limited investigations and monitoring activities of WNV have been performed in the country. The use of animal sentinels is a valuable approach toward investigating the infection presence in an area and to predict the potential occurrence of human outbreaks. Serological investigations in dogs hold several advantages, considering their infection susceptibility, the ease of sample handling, and the evaluation of risk factors of pet owners that share the same habit with their pets. To evaluate the usefulness of such a sero-epidemiological investigation in Namibia, a broad serosurvey was performed in 2022 that included 426 archived domestic dog samples from eight Namibian regions. Although the ELISA prevalence, indicative of Flavivirus infection, was relatively high (16.43%; 95 CI: 13.10-20.39%), the virus neutralization test confirmed only a minority of cases, highlighting a prevalence of 2.82% (95 CI: 1.47-4.90%), significantly lower than in Namibian donkeys and reports from other countries. Variables that could explain the recorded differences remain to be explored, including animal exposure, variable vector presence, distribution, and feeding preferences. The study results suggest the limited usefulness of dogs as sentinels for WNV monitoring in Namibia.

Multi-Year Comparison of Community- and Species-Level West Nile Virus Antibody Prevalence in Birds from Atlanta, Georgia and Chicago, Illinois, 2005-2016.

West Nile virus (WNV) is prevalent in the United States but shows considerable variation in transmission intensity. The purpose of this study was to compare patterns of WNV seroprevalence in avian communities sampled in Atlanta, Georgia and Chicago, Illinois during a 12-year period (Atlanta 2010-2016; Chicago 2005-2012) to reveal regional patterns of zoonotic activity of WNV. WNV antibodies were measured in wild bird sera using ELISA and serum neutralization methods, and seroprevalence among species, year, and location of sampling within each city were compared using binomial-distributed generalized linear mixed-effects models. Seroprevalence was highest in year-round and summer-resident species compared with migrants regardless of region; species explained more variance in seroprevalence within each city. Northern cardinals were the species most likely to test positive for WNV in each city, whereas all other species, on average, tested positive for WNV in proportion to their sample size. Despite similar patterns of seroprevalence among species, overall seroprevalence was higher in Atlanta (13.7%) than in Chicago (5%). Location and year of sampling had minor effects, with location explaining more variation in Atlanta and year explaining more variation in Chicago. Our findings highlight the nature and magnitude of regional differences in WNV urban ecology.

Serological evidence of circulation of West Nile virus in equids in Algerian eastern drylands and its epidemiological risk factors

In order to determine the prevalence of equine infectious anemia virus (EIAV), Usutu virus (USUV), and West Nile virus (WNV) in eastern Algerian drylands, 340 sera from distinct equids have been collected from 2015 to 2017. Serological analysis for the presence of antibodies against EIAV and flaviviruses was performed using commercially available ELISAs. Sera detected positive, doubtful, or negative close to the doubtful threshold in flavivirus ELISA were tested by the virus neutralization test (VNT), using WNV and USUV strains. The prevalence of WNV antibodies with ELISA was 11.47% (39/340) against 13.53% (46/340) by WNV VNT. EIAV antibodies were not detected in any samples. WNV seroprevalence varies with species, breed and location of horses. Only, one equid was positive for both WNV and USUV neutralizing antibodies. This is the first screening on equids sera of EIAV and USUV in Algeria. This study indicate that WNV and possibly USUV have circulated/are circulating in the Algerian equine population, unlike EIAV does not seem to be present.

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

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

High exposure of West Nile virus in equid and wild bird populations in Spain following the epidemic outbreak in 2020.

A cross-sectional study was conducted to assess the circulation and risk factors associated with West Nile virus (WNV) exposure in equine and wild bird populations following the largest epidemic outbreak ever reported in Spain. A total of 305 equids and 171 wild birds were sampled between November 2020 and June 2021. IgG antibodies against flaviviruses were detected by blocking enzyme-linked immunosorbent assay (bELISA) in 44.9% (109/243) and 87.1% (54/62) of unvaccinated and vaccinated equids, respectively. The individual seroprevalence in unvaccinated individuals (calculated on animals seropositive by both bELISA and virus microneutralization test [VNT]) was 38.3% (95%CI: 33.1-43.4). No IgM antibodies were detected in animals tested (0/243; 0.0%; 95%CI: 0.0-1.5) by capture-ELISA. The main risk factors associated with WNV exposure in equids were age (adult and geriatric), breed (crossbred) and the absence of a disinsection programme on the facilities. In wild birds, IgG antibodies against flaviviruses were found in 32.7% (56/171; 95%CI: 26.8-38.6) using bELISA, giving an individual WNV seroprevalence of 19.3% (95%CI: 14.3-24.3) after VNT. Seropositivity was found in 37.8% of the 37 species analysed. Species group (raptors), age (>1-year old) and size (large) were the main risk factors related to WNV seropositivity in wild birds. Our results indicate high exposure and widespread distribution of WNV in equid and wild bird populations in Spain after the epidemic outbreak in 2020. The present study highlights the need to continue and improve active surveillance programmes for the detection of WNV in Spain, particularly in those areas at greatest risk of virus circulation.

Screening of Circulation of Usutu and West Nile Viruses: A One Health Approach in Humans, Domestic Animals and Mosquitoes in Burkina Faso, West Africa.

Usutu virus (USUV) and West Nile virus (WNV) are phylogenetically closely related arboviruses. These viruses mainly follow an enzootic cycle involving mosquitoes and birds, but they occasionally infect humans and other mammals, inducing neurotropic disorders. Since the discovery of USUV, only two human cases have been reported in Africa, including one in Burkina Faso in 2004. Since then, no studies have been conducted to measure the extent of the circulation of this virus in Burkina Faso, and no study regarding the circulation of WNV has been conducted. Our study aimed to determine the seroprevalence of USUV and WNV in blood donations and in animals (horses, dogs, chickens and pigeons) and to perform molecular screening in patients with febrile fever and in Culex quinquefasciatus and Aedes aegypti mosquitoes. The prevalence of USUV and WNV was studied by serological (ELISA and microneutralization tests) and molecular analyses (RT-qPCR) of mosquito, dog, domestic bird, horse, and human samples in Burkina Faso between 2019 and 2021. We detected a very active transmission of both viruses in Burkina Faso. WNV and USUV seroprevalence is particularly high in humans (19.16% and 14.17%, respectively) and horses (17.28% and 6.17%). Molecular screening did not detect WNV or USUV in the mosquito or human samples tested. Our study shows an active spread of USUV and WNV in Burkina Faso, especially for WNV. This study highlights the value of developing surveillance programs to better prevent, detect, and alert people to USUV and WNV circulation in both primary and incidental hosts.

West Nile Virus Seroprevalence and Cross-Neutralization in Sera from Eastern and Central Sudan

Objectives: In regions with co-existing flaviviruses, the diagnosis of previous West Nile virus (WNV) infections is challenging due to cross-reacting antibodies. The aim of the study was to determine the frequency of previous WNV infections in sera from three Sudanese states by excluding potentially dengue virus (DENV) and ZIKV cross-reacting sera and to determine the percentage of WNV cross-neutralizing sera from individuals with previous DENV infection. Methods: Serum samples from Kassala, North Kordofan, and Red Sea state were screened for antibodies against DENV by ELISA. Sera without DENV antibodies (N = 106) and a matched set of sera with DENV antibodies (N = 108) was selected. In all blood samples the frequency of WNV-neutralizing antibodies and the antibody titers were measured with microplate neutralization assays. DENV and Zika virus (ZIKV) microplate neutralization assays were performed with all WNV neutralizing sera of the DENV negative group. Results: A fraction of 30.2% of the DENV antibody negative sera neutralized WNV. The seroprevalence increased with age from 9.5% to 41.7%. Men and women were equally affected. The percentage of DENV positive sera that neutralized WNV was 83.3%. DENV positive sera had higher WNV neutralization titers than DENV negative sera. Conclusions: A significant fraction of the DENV antibody negative sera from three regions in Sudan showed serologic evidence of previous WNV infection. In comparison, the large majority of DENV antibody positive sera had WNV neutralizing antibodies. Studies are needed to identify clinical cases of WNV infection and to determine whether individuals with cross-neutralizing antibodies are protected from WNV disease.

Seroprevalence Rates against West Nile, Usutu, and Tick-Borne Encephalitis Viruses in Blood-Donors from North-Western Romania.

Introduction: West Nile virus (WNV), Usutu virus (USUV), and the tick-borne encephalitis virus (TBEV) are all arboviruses belonging to Flaviviridae family. All are characterized by vectorial transmission and sometimes associated with neuroinvasive infections. The circulation of these viruses is considered endemic in parts of Europe, with human cases reported in many countries. Among hosts, the viruses are vectored by hematophagous arthropods, such as mosquitoes (WNV, USUV) and ticks (TBEV). Considering the currently outdated knowledge regarding the epidemiology of these viruses in Romania, the aim of our study was to assess the seroprevalence rates of WNV, USUV, and TBEV among healthy blood donors in north-western Romania. Methods: Human blood samples from healthy donors were collected between November 2019 and February 2020 in six counties from the north-western region of Romania. The samples were serologically tested by ELISA and serum neutralization test. Results: Overall, we obtained a seroprevalence of 3.17% for WNV, 0.08% for TBEV, and 0% for USUV. Conclusion: Despite the low seroprevalence of WNV, USUV, and TBEV in our study, we highlight the need for continuous nationwide vector and disease surveillance and implementation of control measures. Further research is required for an optimal overview of the epidemiological status of the Romanian population regarding these flaviviruses together with countrywide awareness campaigns.

Seroprevalence of West Nile Virus in Regular Blood Donors Referred to the Blood Bank of Kurdistan Province, Iran

Background: West Nile virus is an infection that is most commonly caused by infected mosquito bites, however, blood transfusions, organ transplants, breast feeding, pregnant mother-to-the-fetus transmission, and occupational transmission among laboratory and medical staff are also the less common routes of infection. Given the endemic nature of this virus in the Middle East, the aim of this study was to investigate the presence of this virus in regular blood donors, as the reliable source of blood supply needed for patients in hospitals.&#x0D; Methods: In this descriptive-analytical study, venous blood samples were collected from 259 regular blood donors referred to the Blood Transfusion Organization of Kurdistan. After separating blood serum, the amount of IgM and IgG antibodies against West Nile virus was measured via ELISA test.&#x0D; Results: Concerning antibodies, IgG and IgM against West Nile virus were positive in 14 patients (5.4%) and 3 patients (1.2%), respectively. Seropositive IgG levels were observed in 11 patients over the age of 40 (12.5%) but only in 3 patients under 40 years of age (1.8%). The difference was statistically significant (OR = 7.95; 95% CI: 2.16–29.32; p &lt; 0.01).&#x0D; Conclusion: Given the value of blood and blood products obtained from regular blood donors for therapeutic purposes and the significant prevalence of the virus and considering the presence of cases with positive IgM, it seems necessary to screen blood donors in blood transfusion centers in the western parts of Iran.

West Nile Virus Seroprevalence in Manisa Province: A Population-based Study.

West Nile Virus (WNV), which causes widespread outbreaks in different parts of the world, is a risk to public health in Turkey, too. Community-based study data are needed to identify measures against possible outbreaks. This study aimed to determine the seroprevalence of community-based WNV in Manisa and to investigate the relationship between sociodemographic and socioeconomic variables. We included individuals older than two years of age (N=1,317,917) registered in the Manisa Province Family Medicine Information System. Selected participants (n=1233) were determined by a simple random sampling method. Specific IgG antibodies against WNV were investigated in serum samples using a commercial ELISA test (Euroimmun, Germany). The relationship between age, gender, location, education and income level, occupation, population density, altitude, the location of the toilet in the house, and the presence of hypertension, diabetes mellitus and cardiovascular disease variables were analyzed by chi-square, Fisher's exact test and t-test. Adjusted odds ratio (OR) with95% confidence interval (CI) for each variable were calculated by the logistic regression method to explain potential risks. WNV IgG antibodies were detected in 47 (3.8%) sera samples by ELISA. Seroprevalence was significantly correlated with independent variables of advanced age, presence of hypertension, diabetes mellitus and cardiovascular disease, low level of education and income, living in low altitude areas and the location of the toilet. In multivariate analysis; age (every one-year increase) (OR:1.05; 95% CI:1.02-1.07; p <0.001), equivalent annual income per capita below 3265 TL (OR:3.21; 95% CI: 1.53-6.73; p=0.002), and living areas below 132 meters altitude (OR=3.21; 95% CI 1.26-8.15; p=0.014) were found to be the risk factors for WNV seropositivity. In Manisa province, WNV IgG seroprevalence was detected as 3.8% with ELISA method. Older age, low income and living in regions with a low altitude were found to be associated with increased seropositivity significantly.

Seroprevalence and Risk Factors for Equine West Nile Virus Infections in Eastern Germany, 2020.

West Nile virus (WNV) infections were first detected in Germany in 2018, but information about WNV seroprevalence in horses is limited. The study’s overall goal was to gather information that would help veterinarians, horse owners, and veterinary-, and public health- authorities understand the spread of WNV in Germany and direct protective measures. For this purpose, WNV seroprevalence was determined in counties with and without previously registered WNV infections in horses, and risk factors for seropositivity were estimated. The cohort consisted of privately owned horses from nine counties in Eastern Germany. A total of 940 serum samples was tested by competitive panflavivirus ELISA (cELISA), and reactive samples were further tested by WNV IgM capture ELISA and confirmed by virus neutralization test (VNT). Information about potential risk factors was recorded by questionnaire and analyzed by logistic regression. A total of 106 serum samples showed antibodies against flaviviruses by cELISA, of which six tested positive for WNV IgM. The VNT verified a WNV infection for 54 samples (50.9%), while 35 sera neutralized tick-borne encephalitis virus (33.0%), and eight sera neutralized Usutu virus (7.5%). Hence, seroprevalence for WNV infection was 5.8% on average and was significantly higher in counties with previously registered infections (p = 0.005). The risk factor analysis showed breed type (pony), housing in counties with previously registered infections, housing type (24 h turn-out), and presence of outdoor shelter as the main significant risk factors for seropositivity. In conclusion, we estimated the extent of WNV infection in the resident horse population in Eastern Germany and showed that seroprevalence was higher in counties with previously registered equine WNV infections.

Spread of West Nile Virus and Usutu Virus in the German Bird Population, 2019-2020.

West Nile virus (WNV) and Usutu virus (USUV) are important flaviviruses circulating in Germany. While USUV was first reported more than 10 years ago, WNV has only reached the country in 2018. Wild birds are important amplifying hosts for both viruses. Therefore, we have been monitoring the bird population in different regions of Germany by a previously established network for many years. This report summarizes the results of molecular and/or serological methods of 2345 blood samples from birds of 22 different orders and over 2900 bird carcasses from 2019 and 2020. USUV RNA circulation was found in different regions of Germany, with emphasis on USUV lineages Europe 3 and Africa 3. Increased evidence of USUV lineage Europe 2 was detected in eastern Germany. WNV RNA was found only in birds from the eastern part of the country. The seroprevalence for USUV was between 3.11% and 7.20% in all three regions investigated, whereas the WNV seroprevalence spanned from 14.77% to 16.15% in eastern Germany, with a noticeable tendency for a westward and southward expansion in both years. Thus, wild bird monitoring for WNV and USUV can serve as an early warning system for a human exposure risk.