First human case of West Nile virus neuroinvasive infection in Italy, September 2008 - case report

First seroprevalence study of West Nile Virus (WNV) infection in blood donors after the upsurge of West Nile Neuroinvasive Disease (WNND) cases in southern Italy in 2023

BACKGROUND

Mosquito-borne diseases are an emerging threat in Europe. West Nile virus (WNV) is an arbovirus commonly transmitted in an enzootic cycle involving ornithophilic mosquitoes as major vectors. In recent years, global climate change has been identified as a significant driver of the increased spread of this virus. In Italy, outbreaks of WNV infection have been recorded every year in northern Italy. The Apulia region of southern Italy was not considered a high-risk region until 2023, when an unexpected increase in WNV infections occurred. The aim of this study was to evaluate the prevalence of anti-WNV antibodies in a wide sample of blood donors in the Apulia region of southern Italy enrolled between November 2023 and February 2024. In addition, the use of protective measures against mosquito bites was assessed.

METHODS

A retrospective cross-sectional study was conducted on a total of 1,579 blood donors. All sera were tested for anti-WNV IgG by ELISA. Reactive serum samples were also tested by CLIA and by the plaque reduction neutralization test (PRNT). All healthy donors answered a short anonymous questionnaire. Data analysis was performed using StataMP14.0® (StataCorp LLC, CollegeStation, TX77845-4512, USA).

RESULTS

The median age was 47 years (IQR: 37-53), and 75% were male. The questionnaires administered revealed that 68.6% of the subjects had not made any trips in the few weeks prior to blood sampling, and 30.5% remembered being bitten by mosquitoes in the previous 15 days or longer. While 17 samples tested by ELISA were positive for anti-WNV IgG, only six were also positive by CLIA testing. Analysis by PRNT for WNV confirmed 5 cases. The findings revealed a WNV seroprevalence of 0.32% (95% CI: 0.07-0.59). Among the subjects who tested positive, none recalled being bitten by mosquitoes or regularly using mosquito repellents.

CONCLUSIONS

Our study suggests the circulation of WNV in Apulia and highlights the potential human health concerns associated with this emerging virus. Strengthening the integrated surveillance system and planning adequate preventive strategies are crucial next steps to address the potential massive spread of WNV in southern Italy.

First Detection of West Nile Virus by Nasopharyngeal Swab, Followed by Phylogenetic Analysis

West Nile Virus, an arthropod-borne RNA virus, may result in severe neurological disease. West Nile neuroinvasive disease is characterized by meningitis, encephalitis, and possible acute flaccid paralysis. Here, we report a case of neuroinvasive WNV in a 65-year-old woman hospitalized for hyperpyrexia, chills, intense asthenia, and continuous vomiting. Within days, her clinical condition worsened with the onset of severe neurological symptoms, leading to her death within 10 days despite supportive therapies being administered. The diagnosis of West Nile disease was made through nucleic acid amplification testing (NAAT) on blood and cerebrospinal fluid. However, in the final stages of the illness, cerebrospinal fluid collection was not possible due to the patient's critical condition, and a nasopharyngeal swab was used instead. The nasopharyngeal swab facilitated the collection of a sample, which was subsequently analyzed for the presence of the virus and allowed for sequencing, showing that it was a strain that had been circulating in Sardinia for some time and had demonstrated its pathogenicity by causing the death of a hawk in 2021. This case report highlights the rapid progression and severity of WNV infection, particularly in vulnerable individuals, and suggests the potential utility of nasopharyngeal swabs as a less invasive option for sample collection. It also underscores the potential for the zoonotic transmission of the virus from birds to humans through vectors, emphasizing the importance of monitoring and controlling WNV outbreaks, especially in regions where such circulation is observed.

Perspective on donor-derived infections in Italy

BACKGROUND

Expected and unexpected donor-derived infections (DDI) are a rare event in solid organ transplant (SOT) recipients but are potentially associated with significant morbidity and mortality. To assure the microbial safety of transplantation, both national guidelines and the current, regional, and local epidemiology of infectious diseases must be considered.

METHODS

In the present paper the strategies adopted by the Italian National Center for Transplantation (CNT) since 2003 and their evolution to guarantee the safety of organ transplantation are reported. Starting in 2012 mandatory reporting to the CNT of all adverse reactions was started. The number and type of DDI reported to the CNT are currently being analyzed.

RESULTS

The infectious diseases second opinion has written and updated the guidelines on the safety of organs for transplantation and supported the Italian transplant network for the use of organs from donors with suspected or documented potentially transmissible infections.

CONCLUSION

A transplant safety network was developed in Italy in 2003 and has been updated according to the evolving knowledge and the changing epidemiology. This is an evolving field, and a continuous update of the recommendation is needed.

West Nile Virus Seroprevalence in the Italian Tuscany Region from 2016 to 2019

Although in humans West Nile virus is mainly the cause of mild or sub-clinical infections, in some cases a neuroinvasive disease may occur predominantly in the elderly. In Italy, several cases of West Nile virus infection are reported every year. Tuscany was the first Italian region where the virus was identified; however, to date only two cases of infection have been reported in humans. This study aimed at evaluating the prevalence of antibodies against West Nile virus in the area of Siena Province to estimate the recent circulation of the virus. Human serum samples collected in Siena between 2016 and 2019 were tested for the presence of antibodies against West Nile virus by ELISA. ELISA positive samples were further evaluated using immunofluorescence, micro neutralization, and plaque reduction neutralization assays. In total, 1.9% (95% CI 1.2–3.1) and 1.4% (95% CI 0.8–2.4) of samples collected in 2016–2017 were positive by ELISA and immunofluorescence assay, respectively. Neutralizing antibodies were found in 0.7% (95% CI 0.3–1.5) of samples. Additionally, 0.9% (95% CI 0.4–1.7) and 0.65% (95% CI 0.3–1.45) of samples collected in 2018–2019 were positive by ELISA and immunofluorescence assay, respectively. The prevalence of neutralizing antibodies was 0.5% (95% CI 0.2–1.3). Although no human cases of West Nile infection were reported in the area between 2016 and 2019 and virus prevalence in the area of Siena Province was as low as less than 1%, the active asymptomatic circulation confirms the potential concern of this emergent virus for human health.

Evolutionary Dynamics of the Lineage 2 West Nile Virus That Caused the Largest European Epidemic: Italy 2011-2018

Lineage 2 West Nile virus (WNV) caused a vast epidemic in Europe in 2018, with the highest incidence being recorded in Italy. To reconstruct the evolutionary dynamics and epidemiological history of the virus in Italy, 53 envelope gene and 26 complete genome sequences obtained from human and animal samples were characterised by means of next-generation sequencing. Phylogenetic analysis revealed two Italian strains originating between 2010 and 2012: clade A, which apparently became extinct in 2013–2014, and clade B, which was responsible for the 2018 epidemic. The mean genetic distances in clade B increased over time and with the distance between sampling locations. Bayesian birth-death and coalescent skyline plots of the clade B showed that the effective number of infections and the effective reproduction number (Re) increased between 2015 and 2018. Our data suggest that WNV-2 entered Italy in 2011 as a result of one or a few penetration events. Clade B differentiated mainly as a result of genetic drift and purifying selection, leading to the appearance of multiple locally circulating sub-clades for different times. Phylodynamic analysis showed a current expansion of the infection among reservoir birds and/or vectors.

Economics of One Health: Costs and benefits of integrated West Nile virus surveillance in Emilia-Romagna

Since 2013 in Emilia-Romagna, Italy, surveillance information generated in the public health and in the animal health sectors has been shared and used to guide public health interventions to mitigate the risk of West Nile virus (WNV) transmission via blood transfusion. The objective of the current study was to identify and estimate the costs and benefits associated with this One Health surveillance approach, and to compare it to an approach that does not integrate animal health information in blood donations safety policy (uni-sectoral scenario). Costs of human, animal, and entomological surveillance, sharing of information, and triggered interventions were estimated. Benefits were quantified as the averted costs of potential human cases of WNV neuroinvasive disease associated to infected blood transfusion. In the 2009–2015 period, the One Health approach was estimated to represent a cost saving of €160,921 compared to the uni-sectoral scenario. Blood donation screening was the main cost for both scenarios. The One Health approach further allowed savings of €1.21 million in terms of avoided tests on blood units. Benefits of the One Health approach due to short-term costs of hospitalization and compensation for transfusion-associated disease potentially avoided, were estimated to range from €0 to €2.98 million according to the probability of developing WNV neuroinvasive disease after receiving an infected blood transfusion.

Emerging arboviral human diseases in Southern Europe

Southern Europe is characterized by unique landscape and climate which attract tourists, but also arthropod vectors, some of them carrying pathogens. Among several arboviral diseases that emerged in the region during the last decade, West Nile fever accounted for high number of human cases and fatalities, while Crimean-Congo hemorrhagic fever expanded its geographic distribution, and is considered as a real threat for Europe. Viruses evolve rapidly and acquire mutations making themselves stronger and naive populations more vulnerable. In an effort to tackle efficiently the emerging arboviral diseases, preparedness and strategic surveillance are needed for the early detection of the pathogen and containment and mitigation of probable outbreaks. In this review, the main human arboviral diseases that emerged in Southern Europe are described.

Usutu virus infections in humans: a retrospective analysis in the municipality of Modena, Italy

OBJECTIVE

To monitor the spread and to evaluate the role for public health of Usutu virus (USUV) in an endemic area of Italy.

METHODS

The survey was retrospectively conducted by detecting USUV RNA and USUV antibodies in cerebrospinal fluid and serum samples collected between 2008 and 2011 from 915 patients with or without neurologic impairments in the area of the municipality of Modena, Italy. Organs of birds and pools of mosquitoes were also tested for USUV RNA. Positive samples were partially sequenced and used for phylogenetic analysis.

RESULTS

The presence of USUV RNA (1.1%; 95% confidence interval (CI) 0.6-2.0) was significantly (p <0.05) higher than that of West Nile virus (0%; 95% CI 0-0.33). USUV antibody level was 6.57% (95% CI 4.87-8.82), and it was significantly higher (p <0.05) compared to that of West Nile virus (p 2.96, 95% CI 1.89-4.62). Partial genome sequencing of USUV strains detected in humans, birds and mosquitoes revealed high nucleotide sequence identity within them and with the USUV strains isolated in Central Europe.

CONCLUSIONS

USUV infection in humans is not a sporadic event in the studied area, and USUV neuroinvasiveness has been confirmed.

Molecular epidemiology, evolution and phylogeny of Chikungunya virus: An updating review

Chikungunya virus (CHIKV) is a mosquito-transmitted alphavirus belonging to the Togaviridae family, causing a febrile illness associated with severe arthralgia and rash. In this review, we summarized a series of articles published from 2013 to 2016 concerning CHIKV epidemiology, phylogeny, vaccine and therapies, to give an update of our most recent article written in 2014 (Lo Presti et al.,2014). CHIKV infection was first reported in 1952 from Makonde plateaus and since this time caused many outbreaks worldwide, involving the Indian Ocean region, African countries, American continent and Italy. CHIKV infection is still underestimated and it is normally associated with clinical symptoms overlapping with dengue virus, recurring epidemics and mutations within the viral genome. These characteristics promote the geographical spread and the inability to control vector-mediated transmission of the virus. For these reasons, the majority of studies were aimed to describe outbreaks and to enhance knowledge on CHIKV biology, pathogenesis, infection treatment, and prevention. In this review, 16 studies on CHIKV phylogenetic and phylodinamics were considered, during the years 2013-2016. Phylogenetic and phylodinamic analysis are useful tools to investigate how the genealogy of a pathogen population is influenced by pathogen's demographic history, host immunological milieu and environmental/ecological factors. Phylogenetic tools were revealed important to reconstruct the geographic spread of CHIKV during the epidemics wave and to have information on the circulating strains of the virus, that are important for the prediction and control of the epidemics, as well as for vaccines and antiviral drugs development. In conclusion, this updating review can give a critical appraisal of the epidemiology, therapeutic and phylogenesis of CHIKV, reinforcing the need to monitor the geographic spread of virus and vectors.

The experience of West Nile virus integrated surveillance system in the Emilia-Romagna region: five years of implementation, Italy, 2009 to 2013

Predicting West Nile virus (WNV) circulation and the risk of WNV epidemics is difficult due to complex interactions of multiple factors involved. Surveillance systems that timely detect virus activity in targeted areas, and allow evidence-based risk assessments may therefore be necessary. Since 2009, a system integrating environmental (mosquitoes and birds) and human surveillance has been implemented and progressively improved in the Emilia-Romagna region, Italy. The objective is to increase knowledge of WNV circulation and to reduce the probability of virus transmission via blood, tissue and organ donation. As of 2013, the system has shown highly satisfactory results in terms of early detection capacity (the environmental surveillance component allowed detection of WNV circulation 3–4 weeks before human cases of West Nile neuroinvasive disease (WNND) occurred), sensitivity (capacity to detect virus circulation even at the enzootic level) and area specificity (capacity to indicate the spatial distribution of the risk for WNND). Strong correlations were observed between the vector index values and the number of human WNND cases registered at the province level. Taking into consideration two scenarios of surveillance, the first with environmental surveillance and the second without, the total costs for the period from 2009 to 2013 were reduced when environmental surveillance was considered (EUR 2.093 million for the first scenario vs EUR 2.560 million for the second). Environmental surveillance helped to reduce costs by enabling a more targeted blood unit testing strategy. The inclusion of environmental surveillance also increased the efficiency of detecting infected blood units and further allowed evidence-based adoption of preventative public health measures.

Review of West Nile virus epidemiology in Italy and report of a case of West Nile virus encephalitis

West Nile virus (WNV) is a flavivirus that causes neurological disorders in less than 1 % of infected subjects. Human cases of WNV-associated fever and/or neurological disorders have been reported in Italy since 2008. The first outbreak occurred in the northeastern region of Italy surrounding the Po River and was caused by the Po River lineage 1 strain, and since then, WNV infections have been reported in several regions of central Italy. Although the virus is highly genetically conserved, stochastic mutations in its genome may lead to the emergence of new strains, as was observed in Italy in 2011 with the identification of two new lineage 1 strains, the WNV Piave and WNV Livenza strains. To help further define WNV epidemiology in Italy, we describe a case of an Italian man living in the Po River area who developed fatal encephalitis in 2009 due to infection with the WNV Piave strain. This finding supports the notion that the Piave strain has been circulating in this area of Italy for 2 years longer than was previously believed.

Retrospective space-time analysis methods to support West Nile virus surveillance activities

The steep increase in human West Nile virus (WNV) infections in 2011-2012 in north-eastern Italy prompted a refinement of the surveillance plan. Data from the 2010-2012 surveillance activities on mosquitoes, equines, and humans were analysed through Bernoulli space-time scan statistics, to detect the presence of recurrent WNV infection hotspots. Linear models were fit to detect the possible relationships between WNV occurrence in humans and its activity in mosquitoes. Clusters were detected for all of the hosts, defining a limited area on which to focus surveillance and promptly identify WNV reactivation. Positive relationships were identified between WNV in humans and in mosquitoes; although it was not possible to define precise spatial and temporal scales at which entomological surveillance could predict the increasing risk of human infections. This stresses the necessity to improve entomological surveillance by increasing both the density of trapping sites and the frequency of captures.

Human and entomological surveillance of West Nile fever, dengue and chikungunya in Veneto Region, Italy, 2010-2012

Background

Since 2010 Veneto region (North-Eastern Italy) planned a special integrated surveillance of summer fevers to promptly identify cases of West Nile Fever (WNF), dengue (DENV) and chikungunya (CHIKV). The objectives of this study were (i) To increase the detection rate of imported CHIKV and DENV cases in travellers from endemic areas and promptly identify potential autochthonous cases.(ii) To detect autochthonous cases of WNF, besides those of West Nile Neuroinvasive Disease (WNND) that were already included in a national surveillance.

Methods

Human surveillance: a traveler who had returned within the previous 15 days from endemic countries, with fever >38°C, absence of leucocytosis (leukocyte count <10,000 μL), and absence of other obvious causes of fever, after ruling out malaria, was considered a possible case of CHIKV or DENV. A possible autochthonous case of WNF was defined as a patient with fever >38°C for <7 days, no recent travel history and absence of other obvious causes of fever. Entomologic surveillance: for West Nile (WNV) it was carried out from May through November placing CDC-CO2 traps in five provinces of Veneto Region, while for DENV and CHIKV it was also performed around residences of viremic cases.

Results

Human surveillance: between 2010 and 2012, 234 patients with fever after travelling were screened, of which 27 (11,5%) were found infected (24 with DENV and 3 with CHIKV). No autochthonous case of DENV or CHIKV was detected. Autochthonous patients screened for WNF were 408, and 24 (5,9%) were confirmed cases. Entomologic surveillance: the WNV was found in 10, 2 and 11 pools of Culex pipiens from 2010 to 2012 respectively, in sites of Rovigo, Verona, Venezia and Treviso provinces). No infected Aedes albopictus with DENV or CHIKV was found.

Conclusions

Veneto is the only Italian region reporting WNV human cases every year since 2008. WNV is likely to cause sporadic cases and unforeseeable outbreaks for decades. Including WNF in surveillance provides additional information and possibly an early alert system. Timely detection of DENV and CHIKV should prompt vector control measures to prevent local outbreaks.

Integrated human surveillance systems of West Nile virus infections in Italy: the 2012 experience

In Italy, a West Nile virus (WNV) surveillance plan was firstly implemented in 2008 and 2009 in two affected regions and, since 2010, according to a national plan, a WNV neuroinvasive disease (WNND) surveillance has to be carried out each year during the period 15 June–30 November, in those regions where WNV circulation has been demonstrated among humans, animals or vectors. Moreover, since WNV can be transmitted to humans even by blood transfusions and organ transplants obtained from infected donors, the national surveillance integrates the blood transfusions and organs transplant surveillances too. The paper describes the results of this integrated human surveillance in Italy in 2012. Overall, in 2012, 28 autochthonous confirmed cases of WNND were reported, 14 blood donations were found WNV positive by Nucleic Acid Amplification Test and no solid organ donors tested positive for WNV. Moreover, 17 cases of WNV fever were confirmed in Veneto region. When comparing the number of WNND cases reported to the surveillance system in previous 4 years (43 cases during the period 2008–2011), with those reported in 2012 an important increase was observed in 2012. The geographic distribution of human cases was consistent with the WNV circulation among animals and vectors. Moreover, the implementation of preventive measures for WNV transmission through blood components allowed the detection of blood donors positive for WNV, avoiding the further spread of the disease. Since surveillance strategies and preventive measures are based on the integration among human, animal and vector control activities, the Italian experience could be considered a good example of collaboration among different sectors of public health in a “one health” perspective.

A model of laboratory surveillance for neuro-arbovirosis applied during 2012 in the Emilia-Romagna region, Italy

Arboviruses with neuroinvasive potential are gaining more attention due to the increased number of cases of autochthonous and imported infections in the human host. Diagnosis of infection caused by these viruses in patients with central nervous system (CNS) diseases is still underestimated and these infections represent an emerging threat to public health. We describe a model suitable for the laboratory surveillance of neuro-arbovirosis that was applied in the Emilia-Romagna region, north-eastern Italy, during the 2012 summer season. One hundred and twenty cases of suspected neuroinvasive infection were tested for arboviral agents on the basis of clinical and laboratory signs and epidemiological data. The most common virus detected was Toscana virus (TOSV): anti-TOSV specific antibodies or viral components were detected in 28.3% of the cases; 79.4% of the TOSV cases were in the acute phase of infection. No cases resulted in acute phase for West Nile (WNV), Usutu (USUV), Chikungunya (CHIKV) or Dengue (DENV) virus infection. Conversely, two patients with a history of staying in a tick-borne encephalitis virus (TBEV) endemic area showed a probable TBEV infection. These results emphasize the importance of a complete and 'ready to act' laboratory diagnostic system to be implemented within the larger frame of a regional integrated surveillance system.

Large human outbreak of West Nile virus infection in north-eastern Italy in 2012

Human cases of West Nile virus (WNV) disease have been reported in Italy since 2008. So far, most cases have been identified in north-eastern Italy, where, in 2012, the largest outbreak of WNV infection ever recorded in Italy occurred. Most cases of the 2012 outbreak were identified in the Veneto region, where a special surveillance plan for West Nile fever was in place. In this outbreak, 25 cases of West Nile neuroinvasive disease and 17 cases of fever were confirmed. In addition, 14 WNV RNA-positive blood donors were identified by screening of blood and organ donations and two cases of asymptomatic infection were diagnosed by active surveillance of subjects at risk of WNV exposure. Two cases of death due to WNND were reported. Molecular testing demonstrated the presence of WNV lineage 1 in all WNV RNA-positive patients and, in 15 cases, infection by the novel Livenza strain was ascertained. Surveillance in other Italian regions notified one case of neuroinvasive disease in the south of Italy and two cases in Sardinia. Integrated surveillance for WNV infection remains a public health priority in Italy and vector control activities have been strengthened in areas of WNV circulation.

The complex epidemiological scenario of West Nile virus in Italy

Entomological, veterinary, and human surveillance systems for West Nile virus (WNV) infection have been implemented in Italy since the first detection of the virus in 1998. These surveillance activities documented a progressive increase of WNV activity and spread in different regions and the emergence of new WNV lineages and strains. Italy is a paradigmatic example of the complex epidemiology of WNV in Europe, where sporadic cases of WNV infection, clusters, and small outbreaks have been reported in several regions. In addition, different strains of both WNV lineage 1 and lineage 2 have been identified, even co-circulating in the same area.

Characterization of the mouse neuroinvasiveness of selected European strains of West Nile virus

West Nile virus (WNV) has caused outbreaks and sporadic infections in Central, Eastern and Mediterranean Europe for over 45 years. Most strains responsible for the European and Mediterranean basin outbreaks are classified as lineage 1. In recent years, WNV strains belonging to lineage 1 and 2 have been causing outbreaks of neuroinvasive disease in humans in countries such as Italy, Hungary and Greece, while mass mortality among birds was not reported. This study characterizes three European strains of WNV isolated in Italy (FIN and Ita09) and Hungary (578/10) in terms of in vitro replication kinetics on neuroblastoma cells, LD50 values in C57BL/6 mice, median day mortality, cumulative mortality, concentration of virus in the brain and spinal cord, and the response to infection in the brain. Overall, the results indicate that strains circulating in Europe belonging to both lineage 1 and 2 are highly virulent and that Ita09 and 578/10 are more neurovirulent compared to the FIN strain.

Persistence of anti-West Nile virus-specific antibodies among asymptomatic blood donors in northeastern Italy

The development and persistence of anti-West Nile Virus (WNV) immunoglobulin G (IgG)- and IgM-specific antibodies were investigated in 68 asymptomatic blood donors (BDs) previously tested as positive between October, 2008, and September, 2009, and living in northeastern Italy. Our study showed that WNV-specific IgG titers became negative (41%) or decreased (33%) in a large percentage of BDs, while they increased in a smaller percentage (10%); 16% of BDs showed no titer variation. Reversion to seronegative status within a short time frame suggests that WNV surveillance should be maintained year after year.

Detection of specific antibodies against West Nile and Usutu viruses in healthy blood donors in northern Italy, 2010-2011

Neutralizing antibodies against West Nile (WNV) and Usutu (USUV) viruses were measured in 6000 samples collected, between 1 September 2010 and 30 June 2011, from blood donors living in different districts of Emilia-Romagna, northeastern Italy. On the basis of the microneutralization assay (MNTA), 47 (0.78%) subjects were positive for WNV and 14 (0.23%) for USUV. These results were compared with those obtained 2 years ago and suggest an increased circulation of USUV among humans in Emilia-Romagna.

West Nile virus in Europe: emergence, epidemiology, diagnosis, treatment, and prevention

West Nile virus (WNV), a mosquito-borne flavivirus in the Japanese encephalitis antigenic group, has caused sporadic outbreaks in humans, horses and birds throughout many of the warmer regions of Europe for at least 20 years. Occasional cases of West Nile encephalitis have also been associated with infected blood transfusions and organ donations. Currently, WNV appears to be expanding its geographical range in Europe and causing increasing numbers of epidemics/outbreaks associated with human morbidity and mortality. This brief review reports on the current epidemic situation regarding WNV in Europe, highlighting the clinical, diagnostic and preventive measures available for controlling this apparently emerging human pathogen.

Heterogeneity of West Nile virus genotype 1a in Italy, 2011

West Nile virus (WNV) is currently circulating in several European countries and, over recent decades, concomitantly with enhanced surveillance studies and improved diagnostic capabilities, an increase in the geographical distribution and in the number of cases in Europe has been documented. In Italy in 2011, 14 human cases of WNV neuroinvasive infections due to lineage 1 strains were registered in several Italian regions. Here we report WNV partial sequences obtained from serum samples of two patients living in different regions of Italy (Veneto and Sardinia). Phylogenetic analysis, performed on a fragment (566 nt) of the envelope gene, showed that WNV strains circulating in Italy in 2011 belong to lineage 1a, but are different from lineage 1a strains isolated in 2008–2009.The data reported here are consistent with the hypothesis of multiple recent introductions of WNV lineage 1a strains into Italy.

West Nile virus in north-eastern Italy, 2011: entomological and equine IgM-based surveillance to detect active virus circulation

Since 2008, West Nile Virus (WNV) has expanded its range in several Italian regions, and its yearly recurrence suggests the virus may have become endemic in some areas. In 2011, a new plan based also on the detection of IgM antibodies was implemented in the north-eastern Italian regions of Veneto and Friuli Venezia Giulia, aiming to early detect WNV infections in areas where the virus had already circulated during the previous summers, and in adjacent zones. From July to November 2011, 1880 sera from 521 equine premises were screened by a commercial IgM capture ELISA. Mosquitoes were captured by CDC-CO2 traps at 61 locations in the two regions. Collected mosquitoes were identified, pooled by species/date/location and examined by real-time RT-PCR and sequencing. Passive surveillance was carried out on clinically affected horses and non-migratory wild birds found dead. IgM sero-positive equines were detected in 19 holdings, five in the area with WNV circulation (AWC) and 14 in the surveillance area (SA); 10 more horse premises tested positive to further serological controls within 4 km of the positive holdings. A total of 85,398 mosquitoes of 15 species were collected and 2732 pools examined. Five Culex pipiens pools tested positive for the presence of WNV. Passive surveillance on non-migratory wild birds allowed detection of the virus only in one found dead collared dove (Streptopelia decaocto), of 82 birds sampled. The WNV belonged to the lineage 2, which had been isolated for the first time in Italy earlier in 2011. By the first week of October, nine human cases had been confirmed in the same area. The implementation of a protocol combining IgM screening of horses with surveillance on mosquito vectors proved to be valuable for early detecting WNV circulation.

Surveillance for West Nile, dengue, and chikungunya virus infections, Veneto Region, Italy, 2010

In 2010, in Veneto Region, Italy, surveillance of summer fevers was conducted to promptly identify autochthonous cases of West Nile fever and increase detection of imported dengue and chikungunya in travelers. Surveillance highlighted the need to modify case definitions, train physicians, and when a case is identified, implement vector control measures.

West Nile virus transmission through organ transplantation in north-eastern Italy: a case report and implications for pre-procurement screening

PURPOSE

West Nile virus (WNV) transmission through organ transplantation occurs rarely and screening of organ donors for WNV infection remains controversial. This report describes the case of WNV encephalitis in a kidney recipient and the case of asymptomatic WNV infection in the organ donor, both observed at Treviso Hospital, northeastern Italy. After briefly reviewing the literature, we discuss the implications for WNV screening.

METHODS

We reviewed medical, laboratory and epidemiological records at our hospital, and the literature concerning cases of organ-transmitted WNV infections and WNV screening of organ donors in Italy and worldwide.

RESULTS

The kidney recipient was the first confirmed case of WNV infection notified in northeastern Italy in 2011, and the first case of WNV infection in a cluster of four transplant recipients who acquired the infection from a common organ donor. The organ donor, whose WNV infection was only retrospectively diagnosed by IgM detection, represents the index case of a WNV outbreak in the Treviso Province. Screening of her blood prior to organ recovery did not show detectable levels of WNV nucleic acid with the use of quantitative real-time polymerase chain reaction.

CONCLUSIONS

This report emphasizes that transplant-acquired WNV neuroinvasive disease can be particularly severe. We suggest that pre-procurement screening of organ donors by testing blood with both WNV IgM capture ELISA and a sensitive nucleic acid testing should be adopted during the transmission season in the present Italian epidemiological setting.

Species Composition and WNV Screening of Mosquitoes from Lagoons in a Wetland Area of the Algarve, Portugal

The aim of this study was to evaluate mosquito abundance, species diversity, larval and adult population dynamics in seven lagoons integrated in the wetland coastal system of the Algarve, Portugal, in the summer of 2007, as well as the screening of these for West Nile virus (WNV). WNV has been isolated from mosquitoes in this region, in the summer of 2004, next to the putative area of infection of two linked human WN cases. Adult mosquitoes were collected with CDC traps baited with CO(2), and potential breeding sites were surveyed for immature stages. Morphological identification of 1,432 adult mosquitoes and 85 larvae revealed the presence of 10 species: Anopheles atroparvus, Anopheles algeriensis, Coquillettidia richiardii, Culex modestus, Culex pipiens, Culex theileri, Culex univittatus, Culiseta longiareolata, Aedes caspius, and Aedes detritus. Adult mosquito peak densities were recorded in July, contrasting with null larval breeding in the same month in the surveyed biotopes. Most abundant species were C. pipiens (52%), C. theileri (29%), and A. caspius (11%). Lagoon Salgados and Quinta das Salinas, exhibited the highest similarity of culicid fauna, despite being most distant from each other, Female mosquitoes (1,249 specimens) screened by RT-PCR, did not reveal WNV products. However, previous detection of WNV activity in this area, susceptible to re-introductions, demands for continued vigilance.

Phylogenetic analysis of West Nile virus isolates, Italy, 2008-2009

To determine the lineage of West Nile virus that caused outbreaks in Italy in 2008 and 2009, several West Nile virus strains were isolated from human specimens and sequenced. On the basis of phylogenetic analyses, the strains isolated constitute a distinct group within the western Mediterranean cluster.

Retrospective diagnosis of West Nile virus infection in a patient with meningoencephalitis in Tuscany, Italy

We report a case of West Nile virus (WNV) infection in a symptomatic woman living in Tuscany in 2007. A retrospective analysis on cerebrospinal fluids drawn from people affected by neurological diseases with unknown etiology allowed the identification of a case of WNV infection before the WNV outbreak in the Northeast Italy in 2008. This emphasizes the importance of maintaining a high level of epidemiological surveillance all over the Italian territory.

A recombinant influenza A virus expressing domain III of West Nile virus induces protective immune responses against influenza and West Nile virus

West Nile virus (WNV) continues to circulate in the USA and forms a threat to the rest of the Western hemisphere. Since methods for the treatment of WNV infections are not available, there is a need for the development of safe and effective vaccines. Here, we describe the construction of a recombinant influenza virus expressing domain III of the WNV glycoprotein E (Flu-NA-DIII) and its evaluation as a WNV vaccine candidate in a mouse model. FLU-NA-DIII-vaccinated mice were protected from severe body weight loss and mortality caused by WNV infection, whereas control mice succumbed to the infection. In addition, it was shown that one subcutaneous immunization with 10⁵ TCID₅₀ Flu-NA-DIII provided 100% protection against challenge. Adoptive transfer experiments demonstrated that protection was mediated by antibodies and CD4+T cells. Furthermore, mice vaccinated with FLU-NA-DIII developed protective influenza virus-specific antibody titers. It was concluded that this vector system might be an attractive platform for the development of bivalent WNV-influenza vaccines.

Phylogeography and epidemiological history of West Nile virus genotype 1a in Europe and the Mediterranean basin

Aim of this study was to reconstruct the temporal and spatial phylodynamics of WNV-1a, the genotype to which the majority of European/Mediterranean viral strains belongs, by using sequences retrieved from public databases. WNV-1a isolates segregated into two major clades: the recent West Mediterranean sequences formed a single monophyletic group within clade A. Clade B included sequences from East Mediterranean and America. Phylogeographic analysis suggested that WNV-1a probably originated in sub-Saharan Africa in the early XXth century, and then spread northwards since the late 1970s, via two routes: one crossing Eastern Mediterranean and the other the Western Mediterranean countries. Our data suggest that the circulation of the virus in a given geographical area usually precedes the onset of the outbreak by one year or more, and underline the importance of the spatial-temporal phylodynamics reconstruction in clarifying the recent epidemiology and in setting up an efficient surveillance system for emerging/reemerging zoonosis.

Two new real-time quantitative reverse transcription polymerase chain reaction assays with unique target sites for the specific and sensitive detection of lineages 1 and 2 West Nile virus strains

Two novel 1-step real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) assays for the simultaneous detection of West Nile virus (WNV) lineage 1 and 2 strains were developed. Primers and the probe of assay 1 target the 5'-untranslated region (UTR), whereas the amplicon of assay 2 is located in the nonstructural region NS2A, which enables an unambiguous and independent WNV diagnosis based on 2 different amplicons. Both assays allow the detection of as few as 2-4 genome copies of WNV strains NY99, Uganda B956, Kunjin, and Sarafend (all cultured on Vero cells). A new synthetic RNA mutant of the 5'-UTR amplicon, which contains 6 twist inverted base-pair changes at the probe attachment site, was used as external calibrator control.

West Nile virus

West Nile virus (WNV) is responsible for thousands of cases of morbidity and mortality in birds, horses, and humans. Epidemics were localized to Europe, Africa, the Middle East, and parts of Asia, and primarily caused a mild febrile illness in humans. In the late 1990s, the virus became more virulent and spread to North America. In humans, the clinical presentation ranges from asymptomatic, seen frequently, to encephalitis/paralysis and death, seen rarely. There is no FDA (Food and Drug Administration)-licensed vaccine for human use, and the only recommended treatment is supportive care. Often, there is a long recovery period. This article reviews the current literature summarizing the molecular virology, epidemiology, clinical manifestations, pathogenesis, diagnosis, treatment, immunology, and protective measures against WNV and WNV infections in humans.

A VLP-based vaccine targeting domain III of the West Nile virus E protein protects from lethal infection in mice

Background

Since its first appearance in the USA in 1999, West Nile virus (WNV) has spread in the Western hemisphere and continues to represent an important public health concern. In the absence of effective treatment, there is a medical need for the development of a safe and efficient vaccine. Live attenuated WNV vaccines have shown promise in preclinical and clinical studies but might carry inherent risks due to the possibility of reversion to more virulent forms. Subunit vaccines based on the large envelope (E) glycoprotein of WNV have therefore been explored as an alternative approach. Although these vaccines were shown to protect from disease in animal models, multiple injections and/or strong adjuvants were required to reach efficacy, underscoring the need for more immunogenic, yet safe DIII-based vaccines.

Results

We produced a conjugate vaccine against WNV consisting of recombinantly expressed domain III (DIII) of the E glycoprotein chemically cross-linked to virus-like particles derived from the recently discovered bacteriophage AP205. In contrast to isolated DIII protein, which required three administrations to induce detectable antibody titers in mice, high titers of DIII-specific antibodies were induced after a single injection of the conjugate vaccine. These antibodies were able to neutralize the virus in vitro and provided partial protection from a challenge with a lethal dose of WNV. Three injections of the vaccine induced high titers of virus-neutralizing antibodies, and completely protected mice from WNV infection.

Conclusions

The immunogenicity of DIII can be strongly enhanced by conjugation to virus-like particles of the bacteriophage AP205. The superior immunogenicity of the conjugate vaccine with respect to other DIII-based subunit vaccines, its anticipated favourable safety profile and low production costs highlight its potential as an efficacious and cost-effective prophylaxis against WNV.

False-positive transcription-mediated amplification assay detection of West Nile virus in blood from a patient with viremia caused by an Usutu virus infection

Detection of West Nile virus (WNV) by nucleic acid amplification technology (NAAT) is used widely to screen blood and organ donations in areas where WNV is endemic. We report a false-positive result of a WNV transcription-mediated amplification assay (TMA) in a patient with viremia that was caused by Usutu virus, a mosquito-borne flavivirus.

Epidemiology of west nile in europe and in the mediterranean basin

In the last 30 years several cases of West Nile (WN) virus infection were reported in horses and humans in Europe and in the Mediterranean Basin. Most of them were determined by strains of the Lineage 1 included in the European Mediterranean/Kenyan cluster. Strains of this cluster are characterised by a moderate pathogenicity for horses and humans and limited or no pathogenicity for birds. In recent years, however, WN cases determined by strains grouped in the Israeli/American cluster of Lineage 1 or in the lineage 2 have been reported in Hungary and Austria. The role of migrating birds in introducing new viruses to Europe has been often demonstrated. The migratory birds, which may be infected in their African wintering places, carry the virus northward to European sites during spring migrations. In the past, the virus introduction determined occasional cases of WN. In the recent years, new epidemiological scenarios are developing. In few occasions it has been evidenced the capability of WNV strains of overwintering by using local birds and mosquitoes. Species of Culex amongst mosquitoes and magpies (Pica pica), carrion crows (Corvus corone) and rock pigeons (Columba livia) amongst resident birds are the most probable species involved in this hypothetical WND endemic cycle.

Epidemiology of west nile in europe and in the mediterranean basin

In the last 30 years several cases of West Nile (WN) virus infection were reported in horses and humans in Europe and in the Mediterranean Basin. Most of them were determined by strains of the Lineage 1 included in the European Mediterranean/Kenyan cluster. Strains of this cluster are characterised by a moderate pathogenicity for horses and humans and limited or no pathogenicity for birds. In recent years, however, WN cases determined by strains grouped in the Israeli/American cluster of Lineage 1 or in the lineage 2 have been reported in Hungary and Austria. The role of migrating birds in introducing new viruses to Europe has been often demonstrated. The migratory birds, which may be infected in their African wintering places, carry the virus northward to European sites during spring migrations. In the past, the virus introduction determined occasional cases of WN. In the recent years, new epidemiological scenarios are developing. In few occasions it has been evidenced the capability of WNV strains of overwintering by using local birds and mosquitoes. Species of Culex amongst mosquitoes and magpies (Pica pica), carrion crows (Corvus corone) and rock pigeons (Columba livia) amongst resident birds are the most probable species involved in this hypothetical WND endemic cycle.

Effects of temperature and rainfall on the activity and dynamics of host-seeking Aedes albopictus females in northern Italy

The Asian tiger mosquito, Aedes albopictus, has colonized nearly all the regions of Italy as well as other areas of Europe. During the summer of 2007 the tiger mosquito was responsible for an outbreak of Chikungunya in Italy, when this virus was brought in by a tourist of Indian origin returning from an endemic area. To increase the knowledge of tiger mosquito population dynamics, a survey was carried out from April to November 2008 in the municipalities of Arco and Riva del Garda (northern Italy) through a Biogents Sentinel™ (BG)-trap sampling. In particular, the aim of the study was to evaluate the influence of temperature and rainfall on the activity and dynamics of A. albopictus host-seeking females. The seasonal emergence of host-seeking females was strongly influenced by the minimum temperature, and a lower threshold of 13°C was identified. In addition, the threshold for the end of adult activity was found at a minimum temperature of 9°C. Host-seeking female abundance was positively affected by the accumulated temperatures over the period 3 and 4 weeks before the sampling week, possibly as a consequence of the positive effect of accumulated temperatures on larval density. Instead, accumulated precipitation over 1-4 weeks before sampling was negatively correlated with host-seeking female abundance. Finally, the activity of host-seeking females, estimated by the weekly increment in female abundance, was positively affected by the total abundance of females and by mean weekly temperatures. Our study provides useful information for predicting the dynamics of host-seeking Ae. albopictus females in northern Italy and for designing control strategies for preventing arbovirus outbreaks in areas colonized by Ae. albopictus.

West Nile virus transmission in 2008 in north-eastern Italy

After 10 years, West Nile virus (WNV) re-emerged in Italy in August 2008. As on 31 December 2008, the infection affected eight Provinces in three Regions (Emilia Romagna, Veneto, Lombardy), where a total of 794 cases of WNV infection in 251 equine stables were detected on the basis of the clinical signs and as a result of a serological screening in horses living in the area. Only 4.0% (32/794) of the serologically positive animals showed clinical signs, and the 32 clinical cases were reported in 18 different farms. The observed case-fatality rate was 15.6% (5/32). The confirmed clinical cases were detected from end August to mid October. Significant levels of positivity by RT-PCR were also observed in magpies (Pica pica) (9.1%, 95% confidence levels: 6.1-13.4%), carrion crows (Corvus corone) (7.4%, 95% confidence levels: 3.6-14.4%) and rock pigeons (Columba livia) (12.9%, 95% confidence levels: 7.6-21.2%).

Is Culex modestus (Diptera: Culicidae), vector of West Nile virus, spreading in the Dombes area, France?

As a main vector of West Nile (WN) virus (family Flaviviridae, genus Flavivirus) in Europe, Culex modestus Ficalbi (Diptera: Culicidae) is commonly found in delta regions, lakes, and ponds. The Dombes area is located along one of the main corridors of bird migrations in France and lies 300 km north of the Camargue region, a frequent focus of WN virus circulation. It is an important breeding, wintering, and stopover site for many bird species that are putative carriers of viruses of different kinds. It is also a continental wetland with approximately =1200 fish farming ponds, scattered over the area, that provide suitable breeding sites for Cx. modestus. This article reports an entomological study based on larval surveys conducted in ponds in 2007 to assess the prevalence and abundance of Cx. modestus in the Dombes. Using the larval survey as an ecological screening test, we investigated the proportion of ponds found positive for Cx. modestus, and the relative abundance of this species was estimated in larval samples. We found that its pond distribution was more extensive in the 2007 survey than in that conducted in the 1970s. Survey methods and meteorological and anthropological factors that could account for the differences or variations between the findings of the two investigations are discussed.

Detection of novel insect flavivirus sequences integrated in Aedes albopictus (Diptera: Culicidae) in Northern Italy

The presence of DNA sequences integrated from a new flavivirus related to Cell Fusing Agent and Kamiti River Virus was identified in wild Aedes albopictus mosquito populations from the provinces of Trentino and Padova, Northern Italy. Field work was developed during August-October 2007 with BG-traps, and mosquitoes were screened for flavivirus and alphavirus. No alphavirus was detected, indicating that Chikungunya virus is not present in these mosquitoes in Trentino and Padova area. However, 21% of the pools were positive for flavivirus, further recognised with BLAST as similar to Kamiti River Virus. Phylogenetical analysis with 708 nucleotides from the NS5 gene identified this virus as a new member of the insect flavivirus clade, together with others like Kamiti River Virus, Cell Fusing Agent or Culex flavivirus, and in the group of those transmitted by Aedes. Furthermore, the treatment with RNAse, indicated that this flavivirus should be integrated in the genome of Ae. albopictus. These results propose that these sequences are transmitted by both sexes, and with different prevalence in the studied populations, and support the idea of a widespread distribution of integrated genomes in several mosquitoes from different areas, as first demonstrated with Cell Silent Agent. Evolutionary implications of this discovery and application in flavivirus phylogeny are discussed.

Overview of emerging arboviruses

Numerous arboviral outbreaks during the past decade have demonstrated that arthropod-borne pathogens continue to be significant public and animal health threats. These outbreaks have occurred globally and have not been limited to tropical or developing countries, as people and goods can be moved anywhere in the world within days. Several examples of recent outbreaks have been described, including how they were identified, tracked and the resulting outcomes from these events. Fortunately, scientific research, including advances in rapid detection of this diverse group of pathogens, has also been progressing. While arboviruses are likely to continually emerge and re-emerge, improved scientific technologies and approaches will hopefully make each future epidemic less likely to occur.

Changing patterns of West Nile virus transmission: altered vector competence and host susceptibility

West Nile virus (WNV) is a flavivirus (Flaviviridae) transmitted between Culex spp. mosquitoes and avian hosts. The virus has dramatically expanded its geographic range in the past ten years. Increases in global commerce, climate change, ecological factors and the emergence of novel viral genotypes likely play significant roles in the emergence of this virus; however, the exact mechanism and relative importance of each is uncertain. Previously WNV was primarily associated with febrile illness of children in endemic areas, but it was identified as a cause of neurological disease in humans in 1994. This modulation in disease presentation could be the result of the emergence of a more virulent genotype as well as the progression of the virus into areas in which the age structure of immunologically naïve individuals makes them more susceptible to severe neurological disease. Since its introduction to North America in 1999, a novel WNV genotype has been identified that has been demonstrated to disseminate more rapidly and with greater efficiency at elevated temperatures than the originally introduced strain, indicating the potential importance of temperature as a selective criteria for the emergence of WNV genotypes with increased vectorial capacity. Even prior to the North American introduction, a mutation associated with increased replication in avian hosts, identified to be under adaptive evolutionary pressure, has been identified, indicating that adaptation for increased replication within vertebrate hosts could play a role in increased transmission efficiency. Although stable in its evolutionary structure, WNV has demonstrated the capacity for rapidly adapting to both vertebrate hosts and invertebrate vectors and will likely continue to exploit novel ecological niches as it adapts to novel transmission foci.