West Nile virus state of the art report of MALWEST Project

The 2022 West Nile Virus Season in Greece; A Quite Intense Season

Since 2010, the West Nile virus (WNV) has been established in Greece. We describe the epidemiology of diagnosed human WNV infections in Greece with a focus on the 2022 season. During the transmission period, clinicians were sending samples from suspected cases for testing. Active laboratory-based surveillance was performed with immediate notification of diagnosed cases. We collected clinical information and interviewed patients on a timely basis to identify their place of exposure. Besides serological and molecular diagnostic methods, next-generation sequencing was also performed. In 2022, 286 cases of WNV infection were diagnosed, including 278 symptomatic cases and 184 (64%) cases with neuroinvasive disease (WNND); 33 patients died. This was the third most intense season concerning the number of WNND cases, following 2018 and 2010. Most (96%) cases were recorded in two regions, in northern and central Greece. The virus strain was a variant of previous years, clustering into the Central European subclade of WNV lineage 2. The 2022 WNV season was quite intense in Greece. The prompt diagnosis and investigation of cases are considered pivotal for the timely response, while the availability of whole genome sequences enables studies on the molecular epidemiology of the disease.

Field Evaluation of Commonly Used Adult Mosquito Traps in Greece

Background: Entomological monitoring activities are a major part of mosquito and mosquito-borne diseases surveillance. Several trapping methods are implemented worldwide, aiming to gather data on species composition and their abundance in various study areas. Methods: Several methodological modifications, such as trapping systems baited with attractants or carbon dioxide, have been proposed to increase trap efficiency. The aim of this study was to test different trap types, commonly used in Greece to collect mosquitoes, with the addition of the Biogents Sentinel lure. Moreover, traps were placed in two distinct land types and two different heights above the ground to compare their efficacy. West Nile Virus is endemic in Greece, so we also aimed to detect viral presence and circulation in selected mosquito pools. Results: Adult mosquitoes of Aedes albopictus, Culex pipiens s.l., and Culiseta longiareolata were collected in both study areas. The trap type had a significant impact on the total collections, while the trap position and interaction between trap and position did not significantly affect mosquito catches. WNV was detected in Cx. pipiens s.l. pools examined from the two study areas. Conclusion: This study emphasizes the role of trapping methods as a key component for monitoring and surveillance of adult mosquito populations, reflecting that several trap types present with different mosquito species capture and catch rates.

West Nile Virus in Culex Mosquitoes in Central Macedonia, Greece, 2022

In 2022, Greece was the second most seriously affected European country in terms of the West Nile virus (WNV), after Italy. Specifically, Central Macedonia was the region with the most reported human cases (81.5%). In the present study, 30,816 female Culex pipiens sensu lato mosquitoes were collected from May to September 2022 in the seven regional units of Central Macedonia; they were then grouped into 690 pools and tested for WNV, while next-generation sequencing was applied to the samples, which showed a cycle threshold of Ct < 30 in a real-time RT-PCR test. WNV was detected in 5.9% of pools, with significant differences in the detection rate among regional units and months. It is of interest that in the Thessaloniki regional unit, where most of the human cases were observed, the virus circulation started earlier, peaked earlier, and lasted longer than in the other regional units. All sequences clustered into the Central European subclade of WNV lineage 2, and the virus strain differed from the initial Greek strain of 2010 by 0.52% and 0.27% at the nucleotide and amino acid levels, respectively. Signature substitutions were present, such as S73P and T157A in the prM and E structural proteins, respectively. The screening of mosquitoes provides useful information for virus circulation in a region with a potential for early warning, while the availability of whole-genome sequences is essential for further studies, including virus evolution.

Seasonal Phenological Patterns and Flavivirus Vectorial Capacity of Medically Important Mosquito Species in a Wetland and an Urban Area of Attica, Greece

Seasonal patterns of mosquito population density and their vectorial capacity constitute major elements to understand the epidemiology of mosquito-borne diseases. Using adult mosquito traps, we compared the population dynamics of major mosquito species (Culex pipiens, Aedes albopictus, Anopheles spp.) in an urban and a wetland rural area of Attica Greece. Pools of the captured Cx. pipiens were analyzed to determine infection rates of the West Nile virus (WNV) and the Usutu virus (USUV). The data provided were collected under the frame of the surveillance program carried out in two regional units (RUs) of the Attica region (East Attica and South Sector of Attica), during the period 2017-2018. The entomological surveillance of adult mosquitoes was performed on a weekly basis using a network of BG-sentinel traps (BGs), baited with CO₂ and BG-Lure, in selected, fixed sampling sites. A total of 46,726 adult mosquitoes were collected, with larger variety and number of species in East Attica (n = 37,810), followed by the South Sector of Attica (n = 8916). The collected mosquitoes were morphologically identified to species level and evaluated for their public health importance. Collected Cx. pipiens adults were pooled and tested for West Nile virus (WNV) and Usutu virus (USUV) presence by implementation of a targeted molecular methodology (real-time PCR). A total of 366 mosquito pools were analyzed for WNV and USUV, respectively, and 38 (10.4%) positive samples were recorded for WNV, while no positive pool was detected for USUV. The majority of positive samples for WNV were detected in the East Attica region, followed by the South Sector of Attica, respectively. The findings of the current study highlight the WNV circulation in the region of Attica and the concomitant risk for the country, rendering mosquito surveillance actions and integrated mosquito management programs as imperative public health interventions.

Effect of Education on Improving Knowledge and Behavior for Arboviral Diseases: A Systematic Review and Meta-Analysis

Arboviral diseases are responsible for a high burden of disease in humans, and a significant part of disease risk reduction efforts relies on vector control methods. The elimination of potential breeding sites for the mosquito vectors and a higher level of literacy by the populations at risk could present a sustainable and environmentally friendly solution. This review aims to assess the efficacy of educational interventions for arboviral diseases on knowledge and self-reported behavior. A systematic literature search was performed using Cochrane, EMBASE, Global Health, and PubMed. References of articles retrieved were searched manually for further studies. Critical appraisal of the selected articles was performed using the Effective Public Health Practice Project tool, and studies with a control group were further assessed through the Cochrane's risk of bias tool. A summary narrative of the results and a meta-analysis was conducted. Fourteen studies fulfilling the inclusion criteria were analyzed. Overall, there was an increase in knowledge and in self-reported adoption of protective measures. No effect was found using solely printed material. A meta-analysis was performed separately for the two outcomes measured, which produced a mean standardized difference of 1.86 (95% CI: 1.33-2.39) in knowledge scores compared with the control groups. Regarding the self-reported protective behavior, the results show a summary value of odds ratio of 5.23 (95% CI: 3.09-7.36). Most of the educational interventions had a positive impact on knowledge and self-reported adoption of protective measures. More research producing stronger evidence and evaluating long-term impact is needed.

Reemergence of West Nile Virus Infections in Southern Greece, 2017

Greece experienced the largest European West Nile virus (WNV) outbreak in 2010 since the 1996 Romania epidemic. West Nile virus reemerged in southern Greece during 2017, after a 2-year hiatus of recorded human cases, and herein laboratory findings, clinical features, and geographic distribution of WNV cases are presented. Clinical specimens from patients with clinically suspected WNV infection were sent from local hospitals to the Microbiology Department of Medical School, National and Kapodistrian University of Athens, and were tested for the presence of specific anti-WNV antibodies and WNV RNA. From July to September 2017, 45 confirmed or probable WNV infection cases were identified; 43 of them with an acute/recent infection, of which 24 (55.8%) experienced WNV neuroinvasive disease (WNND). Risk factors for developing WNND included advanced age, hypertension, and diabetes mellitus. A total of four deaths (16.7%) occurred, all in elderly patients aged > 70 years. Thirty-nine cases were identified in regional units that had not been affected before (36 in Argolis and two in Corinth, northeastern Peloponnese, and one in Rethymno, Crete). The remaining four cases were reported from previously affected regional units of northwestern Peloponnese. The reemergence of WNV after a 2-year hiatus of recorded human cases and the spread of the virus in newly affected regions of the country suggests that WNV has been established in Greece and disease transmission will continue in the future. Epidemiological surveillance, intensive mosquito management programs, and public awareness campaigns about personal protective measures are crucial to the prevention of WNV transmission.

Characteristics of One Health surveillance systems: A systematic literature review

The concept of One Health (OH) promotes the decompartmentalisation of human, animal, and ecosystem health for the more efficient and sustainable governance of complex health issues. This means that traditional boundaries between disciplines and sectors must be transgressed and that all relevant stakeholders must be involved in the definition and management of health problems. International efforts have been made to strengthen collaboration across sectors and disciplines and OH surveillance is strongly encouraged at global, national and local-level to efficiently manage hazards involving humans, animals and ecosystems. This concept is intuitively appealing and would suggest the enhanced performance and cost-effectiveness of surveillance systems, as compared to more conventional approaches. Nevertheless, confusion and uncertainty regarding the practical application, outcomes and impacts prevail. We believe that this is due to the lack of a conceptual and methodological framework which would (i) define the characteristics of OH surveillance, and (ii) identify the appropriate mechanisms for inter-sectoral and multi-disciplinary collaboration, to ensure that the surveillance system performs well, with regard to the objective, the context and the health hazard under surveillance. The objective of the study is to define the organisational and functional characteristics of OH surveillance systems, the context in which they are implemented, as well as the influential factors which may obstruct or support their implementation and performance. To achieve this, a systematic literature review of existing OH surveillance systems was conducted using the Prisma guidelines. The selected systems were assessed according to 38 predetermined variables. These allowed the characterisation of their objectives, organisation, functioning, performance and benefits. Data extraction was conducted using a spreadsheet and a database was built using an electronic multiple-choice questionnaire. The literature search identified a total of 1635 records. After the screening phase, 31 references were kept and 22 additional references retrieved from bibliographies were added. From these 53 selected documents, we retrieved 41 different surveillance systems in line with the definition proposed in this study. The analysis of this database enabled the identification of different dimensions and areas of collaboration. Barriers and levers for the implementation of OH surveillance systems were also identified and discussed. Based on our results, we propose a framework to characterise the organisation of collaboration for the governance and operation of an effective OH surveillance system.

Experimental transmission of West Nile Virus and Rift Valley Fever Virus by Culex pipiens from Lebanon

West Nile virus (WNV) and Rift Valley fever virus (RVFV) are two emerging arboviruses transmitted by Culex pipiens species that includes two biotypes: pipiens and molestus. In Lebanon, human cases caused by WNV and RVFV have never been reported. However, the introduction of these viruses in the country is likely to occur through the migratory birds and animal trades. In this study, we evaluated the ability of Cx. pipiens, a predominant mosquito species in urban and rural regions in Lebanon, to transmit WNV and RVFV. Culex egg rafts were collected in the West Bekaa district, east of Lebanon and adult females of Cx. pipiens were experimentally infected with WNV and RVFV Clone 13 strain at titers of 1.6×10⁸ and 1.33×10⁷ plaque forming units (PFU)/mL, respectively. We estimated viral infection, dissemination and transmission at 3, 7, 14 and 19 days post infection (dpi). Results showed that infection was higher for WNV than for RVFV from 3 dpi to 19 dpi. Viral dissemination and transmission started from 3 dpi for WNV; and only from 19 dpi for RVFV. Moreover, Cx. pipiens were able to excrete in saliva a higher number of viral particles of WNV (1028 ± 405 PFU/saliva at 19 dpi) than RVFV (42 PFU/saliva at 19 dpi). Cx. pipiens from Lebanon are efficient experimental vectors of WNV and to a lower extent, RVFV. These findings should stimulate local authorities to establish an active entomological surveillance in addition to animal surveys for both viruses in the country.

West Nile virus (WNV) and Rift Valley fever virus (RVFV) are two emerging mosquito-borne arboviruses mainly transmitted by Culex mosquitoes. WNV considered one of the most important causative agent of viral encephalitis has a wide distribution in many tropical and temperate countries including the Middle East. RVFV is mainly distributed in Sub-Saharan Africa but epizootics were also reported in Egypt, Saudi Arabia and Yemen. The mosquito vector belongs to the Culex pipiens species which includes two biotypes: pipiens and molestus. Both biotypes are the most widely distributed mosquitoes in Lebanon. Using experimental infections of mosquitoes, our study showed that Cx. pipiens populations collected in West Bekaa were susceptible to infection by these two viruses and ensured efficient transmission of WNV and to a lesser extent, RVFV. Our findings may help to prepare a control strategy more adapted to these mosquito vectors.

Emerging Infectious Diseases and Blood Safety: Modeling the Transfusion-Transmission Risk

While the transfusion-transmission (TT) risk associated with the major transfusion-relevant viruses such as HIV is now very low, during the last 20 years there has been a growing awareness of the threat to blood safety from emerging infectious diseases, a number of which are known to be, or are potentially, transfusion transmissible. Two published models for estimating the transfusion-transmission risk from EIDs, referred to as the Biggerstaff-Petersen model and the European Upfront Risk Assessment Tool (EUFRAT), respectively, have been applied to several EIDs in outbreak situations. We describe and compare the methodological principles of both models, highlighting their similarities and differences. We also discuss the appropriateness of comparing results from the two models. Quantitating the TT risk of EIDs can inform decisions about risk mitigation strategies and their cost-effectiveness. Finally, we present a qualitative risk assessment for Zika virus (ZIKV), an EID agent that has caused several outbreaks since 2007. In the latest and largest ever outbreak, several probable cases of transfusion-transmission ZIKV have been reported, indicating that it is transfusion-transmissible and therefore a risk to blood safety. We discuss why quantitative modeling the TT risk of ZIKV is currently problematic.

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During the last 20 years there has been a growing awareness of the threat to blood safety from emerging infectious diseases (EIDs), a number of which are known to be, or are potentially, transfusion-transmissible.

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The transfusion-transmission risk of EID agents can be estimated by risk modeling which can form an important part of risk assessments and inform decisions regarding risk mitigation strategies.

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We describe and compare the methodological principles of two published risk models for estimating the transfusion transmission risk of EIDs.

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We use Zika virus as a case study to demonstrate that reliable risk modeling for EID agents can be problematic due to the uncertainty of the input parameters.

Genetic Contribution of MHC Class II Genes in Susceptibility to West Nile Virus Infection

WNV is a zoonotic neurotropic flavivirus that has recently emerged globally as a significant cause of viral encephalitis. The last five years, 624 incidents of WNV infection have been reported in Greece. The risk for severe WNV disease increases among immunosuppressed individuals implying thus the contribution of the MHC locus to the control of WNV infection. In order to investigate a possible association of MHC class II genes, especially HLA-DPA1, HLA-DQA1, HLA-DRB1, we examined 105 WNV patients, including 68 cases with neuroinvasive disease and 37 cases with mild clinical phenotype, collected during the period from 2010 to2013, and 100 control individuals selected form the Greek population. Typing was performed for exon 2 for all three genes. DQA1*01:01 was considered to be "protective" against WNV infection (25.4% vs 40.1%, P = 0.004) while DQA1*01:02 was associated with increased susceptibility (48.0% vs 32.1%, P = 0.003). Protection against neuroinvasion was associated with the presence of DRB1*11:02 (4.99% vs 0.0%, P = 0.018). DRB1*16:02 was also absent from the control cohort (P = 0.016). Three additional population control groups were used in order to validate our results. No statistically significant association with the disease was found for HLA-DPA alleles. The results of the present study provide some evidence that MHC class II is involved in the response to WNV infection, outlining infection "susceptibility" and "CNS-high-risk" candidates. Furthermore, three new alleles were identified while the frequency of all alleles in the study was compared with worldwide data. The characterization of the MHC locus could help to estimate the risk for severe WNV cases in a country.

Serological monitoring of backyard chickens in Central Macedonia-Greece can detect low transmission of West Nile virus in the absence of human neuroinvasive disease cases

During 2010-13, West Nile virus (WNV) epidemics occurred in Greece with high numbers of human cases. In parallel, WNV serological surveillance utilizing domestic birds was applied mainly in Central Macedonia, as well as in other areas of the country, and allowed efficient detection of WNV activity during this period. The objective of the study was to evaluate the sensitivity of chicken-based WNV surveillance in periods of low-level virus transmission (2014-15) in a well-studied area, i.e. the epicenter of the 2010 WNV epidemic (Central Macedonia), which is considered endemic since then. WNV activity was monitored via determination of antiviral immune responses in juvenile backyard chickens. The birds were sampled twice per transmission period. WNV-specific antibodies were detected by ELISA in 2.8% out of 255 chickens sampled early in the 2014 transmission period (95% CI: 1-6%). Continued virus transmission was detected at the end of the period, as 4.2% out of 240 sampled chickens seroconverted to WNV (95% CI: 2-8%). Although 14 human neuroinvasive cases occurred in Greece during 2014, no such cases were reported in the study area. During the 2015 early warning period, antibodies against WNV were not detected in sampled chickens (n=250, 95% CI: 0-2%). However, humoral immune responses were detected in 6 out of 240 chicken sampled at the end of the transmission period (2.5%; 95% CI: 1-6%), indicating continued WNV activity. No human cases were reported in Greece during 2015. All samples were negative with real-time RT-PCR. Serological surveillance of chickens resulted in identification of areas with low WNV activity levels during 2014-15, and provided indications of its overwintering in Central Macedonia. The findings suggest that surveillance based on serological testing of domestic birds is sensitive and able to detect low-level of WNV enzootic transmission, in the absence of human cases.

Identification of Climatic Factors Affecting the Epidemiology of Human West Nile Virus Infections in Northern Greece

Climate can affect the geographic and seasonal patterns of vector-borne disease incidence such as West Nile Virus (WNV) infections. We explore the association between climatic factors and the occurrence of West Nile fever (WNF) or West Nile neuro-invasive disease (WNND) in humans in Northern Greece over the years 2010–2014. Time series over a period of 30 years (1979–2008) of climatic data of air temperature, relative humidity, soil temperature, volumetric soil water content, wind speed, and precipitation representing average climate were obtained utilising the ECMWF’s (European Centre for Medium-Range Weather Forecasts) Re-Analysis (ERA-Interim) system allowing for a homogeneous set of data in time and space. We analysed data of reported human cases of WNF/WNND and Culex mosquitoes in Northern Greece. Quantitative assessment resulted in identifying associations between the above climatic variables and reported human cases of WNF/WNND. A substantial fraction of the cases was linked to the upper percentiles of the distribution of air and soil temperature for the period 1979–2008 and the lower percentiles of relative humidity and soil water content. A statistically relevant relationship between the mean weekly value climatic anomalies of wind speed (negative association), relative humidity (negative association) and air temperature (positive association) over 30 years, and reported human cases of WNF/WNND during the period 2010–2014 could be shown. A negative association between the presence of WNV infected Culex mosquitoes and wind speed could be identified. The statistically significant associations could also be confirmed for the week the WNF/WNND human cases appear and when a time lag of up to three weeks was considered. Similar statistically significant associations were identified with the weekly anomalies of the maximum and minimum values of the above climatic factors. Utilising the ERA-Interim re-analysis methodology it could be shown that besides air temperature, climatic factors such as soil temperature, relative humidity, soil water content and wind speed may affect the epidemiology of WNV.

Associations of ABO, D, and Lewis blood groups and HLA Class I and Class II alleles with West Nile virus Lineage 2 disease outcome in Greece, 2010 to 2013

BACKGROUND

West Nile virus (WNV) infection, commonly asymptomatic, may cause mild West Nile fever (WNF) or potentially fatal neuroinvasive disease (WNND). An outbreak of 262 cases of the new Lineage 2 strain in Greece in 2010 continued with high mortality (17%) in WNND. The objective was to investigate ABO, D, and Lewis blood groups, as well as HLA Class I and Class II alleles, in relation to WNV Lineage 2 disease morbidity.

STUDY DESIGN AND METHODS

A cohort of 132 Greek WNV cases in 2010 to 2013 (65% male; mean age 64 years; 41% WNF, 59% WNND) was compared to 51,339 healthy WNV-negative blood donors and 246 healthy subjects.

RESULTS

Blood group A was more common in WNV cases (51%) than blood donors (39%) and group O less common (32% vs. 42%). D negativity within group A was higher in WNV than in blood donors (18% vs. 10%, p = 0.044). The frequency of secretors (Lewis(a-b+)) was 60% in WNV and 68% in donors (p = 0.16). HLA alleles C*08, DRB1*O4:O5, and DQB1*O2 occurred significantly less frequently in WNV than controls (p < 0.05 unadjusted for multiple testing) and DRB1*10:O1 more frequently (p = 0.039).

CONCLUSION

This first study of symptomatic WNV Lineage 2 suggests A/D negativity as a new risk factor associated with WNV infection and level of morbidity. Further studies are required of the possibility that HLA C*08, DRB1*O4:O5, and DQB1*O2 are protective alleles and DRB1*10:O1 a "susceptible" allele to WNV infection and the role of secretor status in relation to WNV infection.

West Nile Virus Circulation in Mosquitoes in Greece (2010-2013)

Background of the Study. Following a large West Nile virus (WNV) epidemic in Northern Greece in 2010, an active mosquito surveillance system was implemented, for a 3-year period (2011, 2012, and 2013). Description of the Study Site and Methodology. Using mainly CO2 mosquito traps, mosquito collections were performed. Samples were pooled by date of collection, location, and species and examined for the presence of WNV. Results. Positive pools were detected in different areas of the country. In 2010, MIR and MLE values of 1.92 (95% CI: 0.00-4.57) and 2.30 (95% CI: 0.38-7.49) were calculated for the Serres Regional Unit in Central Macedonia Region. In 2011, the highest MIR value of 3.71(95% CI: 1.52-5.91) was recorded in the Regions of Central Greece and Thessaly. In 2012, MIR and MLE values for the whole country were 2.03 (95% CI: 1.73-2.33) and 2.15 (95% CI: 1.86-2.48), respectively, for Cx. pipiens. In 2013, in the Regional Unit of Attica, the one outbreak epicenter, MIR and MLE values for Cx. pipiens were 10.75 (95% CI: 7.52-13.99) and 15.76 (95% CI: 11.66-20.65), respectively. Significance of Results/Conclusions. The contribution of a mosquito-based surveillance system targeting WNV transmission is highlighted through the obtained data, as in most regions positive mosquito pools were detected prior to the date of symptom onset of human cases. Dissemination of the results on time to Public Health Authorities resulted in planning and application of public health interventions in local level.

Economic appraisal of the public control and prevention strategy against the 2010 West Nile Virus outbreak in Central Macedonia, Greece

OBJECTIVES

The aim of the present paper is to evaluate the economic efficiency of the public control and prevention strategies to tackle the 2010 West Nile Virus (WNV) outbreak in the Region of Central Macedonia, Greece. Efficiency is examined on the basis of the public prevention costs incurred and their potential in justifying the costs arising from health and nuisance impacts in the succeeding years.

STUDY DESIGN

Economic appraisal of public health management interventions.

METHODS

Prevention and control cost categories including control programmes, contingency planning and blood safety testing, are analyzed based on market prices. A separate cost of illness approach is conducted for the estimation of medical costs and productivity losses from 2010 to 2013 and for the calculation of averted health impacts. The averted mosquito nuisance costs to households are estimated on the basis of a contingent valuation study. Based on these findings, a limited cost-benefit analysis is employed in order to evaluate the economic efficiency of these strategies in 2010-2013.

RESULTS

Results indicate that cost of illness and prevention costs fell significantly in the years following the 2010 outbreak, also as a result of the epidemic coming under control. According to the contingent valuation survey, the annual average willingness to pay to eliminate the mosquito problem in the study area ranged between 22 and 27 € per household. Cost-benefit analysis indicates that the aggregate benefit of implementing the previous 3-year strategy creates a net socio-economic benefit in 2013. However the spread of the WNV epidemic and the overall socio-economic consequences, had the various costs not been employed, remain unpredictable and extremely difficult to calculate.

CONCLUSIONS

The application of a post epidemic strategy appears to be of utmost importance for public health safety. An updated well designed survey is needed for a more precise definition of the optimum prevention policies and levels and for the establishment of the various cost/benefit parameters.

West Nile Virus Seroprevalence in the Greek Population in 2013: A Nationwide Cross-Sectional Survey

Cases of West Nile Virus (WNV) disease were recorded for three consecutive years in Greece following the year 2010 outbreak. A cross-sectional serologic survey was conducted to estimate the WNV seroprevalence and assess the ratio of infection to neuroinvasive disease. A stratified left-over sampling methodology was used including age and residence strata. A total of 3,962 serum samples was collected and tested for WNV Immunoglobulin G (IgG) antibodies by Enzyme–Linked Immunosorbent Assay (ELISA). All positive samples were further tested by Plaque Reduction Neutralization Test (PRNT) and WNV Immunoglobulin M (IgM) antibodies. WNV IgG antibodies were detected in 82 samples and 61 were also positive in PRNT representing a weighted seroprevalence of 2.1% (95% C.I.: 1.7–2.6) and 1.5% (95% C.I.: 1.2–2.0), respectively. Multivariable analysis showed that seroprevalence was associated with age and residence. The overall ratio of neuroinvasive disease to infected persons was estimated at 1:376 (95% C.I.: 1:421–1:338), while the elderly people had the highest ratio. This nationwide study provided valuable data regarding the epidemiology of WNV in Greece based on the fact that elderly people have higher risk of being both infected and having severe disease.

Evaluation of Cross-Protection of a Lineage 1 West Nile Virus Inactivated Vaccine against Natural Infections from a Virulent Lineage 2 Strain in Horses, under Field Conditions

Although experimental data regarding cross-protection of horse West Nile virus (WNV) vaccines against lineage 2 infections exist, the cross-protective efficacy of these vaccines under field conditions has not been demonstrated. This study was conducted to evaluate the capability of an inactivated lineage 1 vaccine (Equip WNV) to protect against natural infections from the Nea Santa-Greece-2010 lineage 2 strain. In total, 185 WNV-seronegative horses in Thessaloniki, Greece, were selected during 2 consecutive years (2011 and 2012); 140 were immunized, and 45 were used as controls. Horses were examined for signs compatible with WNV infection. Neutralizing antibody titers against the Greek strain and the PaAn001/France lineage 1 strain were determined in immunized horses. WNV circulation was detected during both years in the study area. It was estimated that 37% and 27% of the horses were infected during 2011 and 2012, respectively. Three control animals developed clinical signs, and the WNV diagnosis was confirmed. Signs related to WNV infection were not observed in the vaccinated animals. The nonvaccinated animals had a 7.58% ± 1.82% higher chance of exhibiting signs than immunized animals (P < 0.05). Neutralizing antibodies raised against both strains in all immunized horses were detectable 1 month after the initial vaccination course. The cross-protective capacity of the lowest titer (1:40) was evident in 19 animals which were subsequently infected and did not exhibit signs. Neutralizing antibodies were detectable until the annual booster, when strong anamnestic responses were observed (geometrical mean titer ratio [GMTR] for lineage 1 of 30.2; GMTR for lineage 2 of 27.5). The results indicate that Equip WNV is capable of inducing cross-protection against natural infections from a virulent lineage 2 WNV strain in horses.

Vector borne infections in Italy: results of the integrated surveillance system for West Nile disease in 2013

The epidemiology of West Nile disease (WND) is influenced by multiple ecological factors and, therefore, integrated surveillance systems are needed for early detecting the infection and activating consequent control actions. As different animal species have different importance in the maintenance and in the spread of the infection, a multispecies surveillance approach is required. An integrated and comprehensive surveillance system is in place in Italy aiming at early detecting the virus introduction, monitoring the possible infection spread, and implementing preventive measures for human health. This paper describes the integrated surveillance system for WND in Italy, which incorporates data from veterinary and human side in order to evaluate the burden of infection in animals and humans and provide the public health authorities at regional and national levels with the information needed for a fine tune response.

Phlebovirus infections in Greece

Sandfly fever viruses are endemic in the Mediterranean region causing to humans asymptomatic or mild infections to severe neurological syndromes. In order to investigate the epidemiology of phlebovirus infections in Greece, samples from 499 patients with acute febrile illness (50.2% accompanied by neurological symptoms) were tested during 2010-2014 by serological and molecular methods. Phlebovirus infection was detected in 40 (8%) patients, 25 of them presenting acute neurological infection. Most cases were observed in the summer, with a peak in August. Increased number of cases was observed in 2013, and three of them were observed in Athens. Toscana virus lineage C RNA was detected in one encephalitis case, while the serological results showed that most cases were caused by phleboviruses belonging to the sandfly fever Naples virus serocomplex. This study provided the first insight into the epidemiology of phleboviral disease in Greece.

Emergence of Equine West Nile Encephalitis in Central Macedonia, Greece, 2010

During the summer of 2010, an outbreak of West Nile virus (WNV) infections attributed to a lineage 2 WNV strain was reported among humans and horses in Central Macedonia, Northern Greece. Here, the clinical and laboratory investigation of horses that showed severe neurological signs due to WNV infection is being described. Specifically, between August and September 2010, 17 horses with neurological signs were detected. WNV infection was confirmed in all 17 clinical cases by applying laboratory testing. The duration of WNV-specific IgM antibodies in sera obtained from seven of the clinically affected horses was relatively short (10-60 days; mean 44 days). In the regional unit of Thessaloniki, (i) seroprevalence of WNV and fatality rate in horses were high (33% and 30%, respectively), and (ii) the ratio of neurological manifestations-to-infections for this virus strain was high (19%). These observations indicate that the strain responsible for the massive human epidemic of 2010 in Greece was also highly pathogenic for horses. This is the first time that WNV infection has been documented in horses with clinical manifestations in Greece. WNV infection should be included in the differential diagnosis of horses with encephalitis in Greece.

Laboratory and surveillance studies following a suspected Dengue case in Greece, 2012

OBJECTIVES

To describe the laboratory assays used to investigate a suspected dengue case in summer 2012 in western Greece and to report the public health response.

DESIGN OF METHODS

Samples from the patient were tested for detection of Dengue virus (DENV) antibodies, NS1 antigen and RNA. Public health professionals interviewed residents of the village, and blood samples taken from 132 persons were tested for antibodies for DENV and West Nile virus (WNV). Samples from 10 persons who reported symptoms in the prior 15 days (including 3 persons who had fever at the time of sampling) were tested for DENV, WNV and additional arboviruses. Entomological missions were organized in the area of potential exposure to investigate the presence of competent DENV vectors.

RESULTS

Based on a combination of serological and molecular methods, DENV infection was excluded, and the problems in the serology, especially in the DENV NS1 antigen, were attributed to interfering factors. A 6.1% WNV seroprevalence was detected in the region, and phlebovirus IgM and IgG antibodies were detected in two of three persons who had fever at the time of sampling. Aedes albopictus adult mosquitoes were present in the region.

CONCLUSIONS

A multi-disciplinary field and laboratory investigation showed no evidence of DENV infection. There is a need for industries to improve the immunometric assays to avoid interference with rheumatoid or other factors, and increased awareness is needed for the evaluation of the diagnostic assays. The high WNV seroprevalence in the investigated region highlights the need for strengthening awareness on vector borne diseases. The presence of Ae. albopictus suggests that the possibility of introduction of DENV exists, and preparedness plans are needed.

West Nile virus outbreak in humans, Greece, 2012: third consecutive year of local transmission

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