West Nile virus: an overview of its spread in Europe and the Mediterranean basin in contrast to its spread in the Americas

West Nile virus population genetics and evolution

West Nile virus (WNV) (Flaviviridae: Flavivirus) is transmitted from mosquitoes to birds, but can cause fatal encephalitis in infected humans. Since its introduction into North America in New York in 1999, it has spread throughout the western hemisphere. Multiple outbreaks have also occurred in Europe over the last 20 years. This review highlights recent efforts to understand how host pressures impact viral population genetics, genotypic and phenotypic changes which have occurred in the WNV genome as it adapts to this novel environment, and molecular epidemiology of WNV worldwide. Future research directions are also discussed.

Rapid molecular detection methods for arboviruses of livestock of importance to northern Europe

Arthropod-borne viruses (arboviruses) have been responsible for some of the most explosive epidemics of emerging infectious diseases over the past decade. Their impact on both human and livestock populations has been dramatic. The early detection either through surveillance or diagnosis of virus will be a critical feature in responding and resolving the emergence of such epidemics in the future. Although some of the most important emerging arboviruses are human pathogens, this paper aims to highlight those diseases that primarily affect livestock, although many are zoonotic and some occasionally cause human mortality. This paper also highlights the molecular detection methods specific to each virus and identifies those emerging diseases for which a rapid detection methods are not yet developed.

Spatio-temporal patterns of distribution of West Nile virus vectors in eastern Piedmont Region, Italy

BACKGROUND

West Nile Virus (WNV) transmission in Italy was first reported in 1998 as an equine outbreak near the swamps of Padule di Fucecchio, Tuscany. No other cases were identified during the following decade until 2008, when horse and human outbreaks were reported in Emilia Romagna, North Italy. Since then, WNV outbreaks have occurred annually, spreading from their initial northern foci throughout the country. Following the outbreak in 1998 the Italian public health authority defined a surveillance plan to detect WNV circulation in birds, horses and mosquitoes. By applying spatial statistical analysis (spatial point pattern analysis) and models (Bayesian GLMM models) to a longitudinal dataset on the abundance of the three putative WNV vectors [Ochlerotatus caspius (Pallas 1771), Culex pipiens (Linnaeus 1758) and Culex modestus (Ficalbi 1890)] in eastern Piedmont, we quantified their abundance and distribution in space and time and generated prediction maps outlining the areas with the highest vector productivity and potential for WNV introduction and amplification.

RESULTS

The highest abundance and significant spatial clusters of Oc. caspius and Cx. modestus were in proximity to rice fields, and for Cx. pipiens, in proximity to highly populated urban areas. The GLMM model showed the importance of weather conditions and environmental factors in predicting mosquito abundance. Distance from the preferential breeding sites and elevation were negatively associated with the number of collected mosquitoes. The Normalized Difference Vegetation Index (NDVI) was positively correlated with mosquito abundance in rice fields (Oc. caspius and Cx. modestus). Based on the best models, we developed prediction maps for the year 2010 outlining the areas where high abundance of vectors could favour the introduction and amplification of WNV.

CONCLUSIONS

Our findings provide useful information for surveillance activities aiming to identify locations where the potential for WNV introduction and local transmission are highest. Such information can be used by vector control offices to stratify control interventions in areas prone to the invasion of WNV and other mosquito-transmitted pathogens.

Identification of suitable areas for West Nile virus outbreaks in equid populations for application in surveillance plans: the example of the Castile and Leon region of Spain

The introduction and rapid spread of West Nile virus (WNV) into new areas such as the American continent, associated also with the severity of the disease in humans and equids has increased concerns regarding the need to better prevent and control future WNV incursions. WNV outbreaks in equids usually occur under specific climatic and environmental conditions and, typically, before detection of WNV cases in humans. Targeting surveillance strategies in areas and time periods identified as suitable for WNV outbreaks in equids may act as an early-warning system to prevent disease in both equids and humans. This study used a GIS-based framework to identify suitable areas and time periods for WNV outbreak occurrence in one of the most important areas of equid production in Spain, i.e. Castile and Leon. Methods and results presented here may help to improve the early detection and control of future WNV outbreaks in Spain and other regions.

Detection of West Nile virus genome and specific antibodies in Iranian encephalitis patients

West Nile virus (WNV) is a mosquito-borne flavivirus which circulates in birds, horses and humans. An estimated 80% of WNV infections are asymptomatic. Fewer than 1% of infected persons develop neuroinvasive disease, which typically presents as encephalitis, meningitis, or acute flaccid paralysis. This study was conducted from January 2008 to June 2009 in Isfahan, Iran. Patients attending the emergency department with fever and loss of consciousness were consecutively included. Cerebrospinal fluids (CSF) were initially analysed through bacteriology and biochemistry examinations, resulting in those with evidence of meningitis being excluded. Patients' CSF and serum were diagnosed by serological and molecular assays. A total of 632 patients with fever and loss of consciousness were tested by CSF analyses. Samples of the remaining patients (39·4%) were referred for WNV investigation. Three (1·2%) of the patients were positive for both serum and CSF by RT–PCR, and six (2·4%) were positive only for IgG antibodies. History of insect bite, and blood transfusion and transplantation were risk factors for being positive by RT–PCR (P=0·048) and being IgG positive (P=0·024), respectively. The results of this study showed that the prevalence of West Nile fever is low in patients with encephalitis.

West Nile virus monitoring in migrating and resident water birds in Iran: are common coots the main reservoirs of the virus in wetlands?

A molecular and serological study was carried out to determine the West Nile virus (WNV) status in different species of wild water birds. From 2003 to 2007, samples were collected from 519 birds representing 26 different species in Iran. Out of 519 serum samples tested for WNV antibodies, 78 (15%) were positive when tested using virus neutralization and immunofluorescence. Antibodies of WNV were detected in 71 out of 131 common coot (Fulica atra) samples. In comparison, only 7 out of 388 birds that were belonged to 25 other species of water birds revealed positive results. For most Anatidae species, no positive duck in serological tests was found. Further, no WNV viral RNA-positive samples were found in this study. Results of this investigation provide important information about the prevalence of WNV in wild water birds in Iran and indicate the potential role and importance of common coots in ecology of WNVs.

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.

Theoretical formulation for mosquito host-feeding patterns: application to a West Nile virus focus of southern France

Host-feeding patterns play a key role in the transmission of vector-borne diseases such as West Nile fever, which involves two kinds of vertebrates, birds and mammals. In this study, we propose a theoretical formulation for mosquito host-feeding patterns using three quantities, as follows: the apparent attractiveness/contact probabilities, the conditional host(-feeding) preferences, and the enzootic versus bridge probabilities. Using results from host-baited trap collections, the quantities defined above were assessed for the most abundant mosquito species in the main West Nile virus focus of southern France. We found that host availability is important in determining the efficiency of bridge vectors, and that even ornithophilic mosquitoes like Culex species, classically classified as enzootic vectors, may turn out to be efficient bridge vectors in certain contexts of host abundance. Our developed theoretical framework can easily be adapted and applied to other experimental data and other vector-borne diseases.

Serological evidence of West Nile virus circulation in Portugal

The circulation of West Nile virus in Portugal was assessed by serological surveys conducted during 2004-2010 in horses and birds. The detection of WNV antibodies in both species in all the years covered by the study as well as the presence of anti-WNV IgM in symptomatic horses that had not traveled outside the country, support the notion that WNV circulates in Portugal.

Re-emergence of West Nile virus in Italy

In August 2008, West Nile disease re-emerged in Italy. The infection is affecting the North Eastern regions and, as of November 2008, has caused 33 clinical cases and five fatalities in horses. Until now, no deaths have been reported in birds. Mosquitoes, blood, serum and tissue samples, from horses and birds, within and around the outbreak area, have been collected and tested by various methods both serologically and virologically. West Nile virus strains have been isolated from blood samples of one horse and one donkey and from pools of brain, kidneys, heart and spleen of a pigeon and three magpies. When compared to the strain isolated during the 1998 Tuscany outbreak, the 255 bp sequence of the genome region coding for the envelope (E) protein of the isolated WNV strains, exhibited a 98.8% and 100% similarity at nucleotide and amino-acid level respectively.

West Nile Virus in the New World: trends in the spread and proliferation of West Nile Virus in the Western Hemisphere

The observed patterns and variations in the ecology, epidemiology, distribution and prevalence of the West Nile Virus (WNV) in different areas of the Western Hemisphere make this pathogen of particular importance as a model for understanding the potential risk factors associated with emerging pathogens worldwide, particularly those involving zoonotic pathogens whose epidemiology involves the potential for vertical transmission in arthropod vector species, and horizontal and vertical transmission within and among vertebrate host species. Record numbers of human WNV cases were recorded in Canada during 2007, with >50% more cases than documented in any previous year. Although overall numbers of human infections recorded in the United States were not exceptionally high during 2007 relative to epidemic levels reported in 2002 and 2003, the state of Oklahoma reported that the highest-ever number of human WNV cases and the numbers of human cases recorded in Canada were 50% higher than previous record levels recorded in 2003. The record and near-record numbers of human WNV infections recorded in several regions of North America during 2007 have important implications for the future management and surveillance of WNV vectors and reservoirs in North America. The spatiotemporal distribution of WNV infections in humans and animals recorded during 2007 in North America and South America have important implications for the surveillance and management of public health threats from WNV in the Western Hemisphere. Serological surveys conducted in areas of intense WNV transmission in the United States have reported low prevalence of antibodies to WNV in human s populations, indicating that additional epidemic outbreaks of human disease from WNV can be expected in the future.

Spread of West Nile virus in Iran: a cross-sectional serosurvey in equines, 2008–2009

We report the first large-scale serosurvey for West Nile virus (WNV) conducted in the equine population in Iran. Blood samples were obtained in 2008–2009 from 1054 equines collected from 260 districts located in 27 provinces. The overall seroprevalence rate for WNV neutralizing antibodies was 23·7%. Marked geographical variations were observed as province-specific seroprevalence rates ranged from 1% to 88%, the highest values being observed in the southern and western parts of the country. The presence of IgM-positive animals (n=9) indicated a recent circulation of WNV in several provinces. Logistic modelling confirmed this result with a significant effect of age on seropositivity. This study revealed extensive circulation of WNV in Iran particularly in southwestern provinces where the virus probably circulates every year.

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.

Simultaneous detection of Rift Valley Fever, bluetongue, rinderpest, and Peste des petits ruminants viruses by a single-tube multiplex reverse transcriptase-PCR assay using a dual-priming oligonucleotide system

The aim of this study was to develop a highly sensitive and specific one-step multiplex reverse transcriptase PCR assay for the simultaneous and differential detection of Rift Valley Fever virus (RVFV), bluetongue virus (BTV), rinderpest virus (RPV), and Peste des petits ruminants virus (PPRV). These viruses cause mucosal lesions in cattle, sheep, and goats, and they are difficult to differentiate from one another based solely on their clinical presentation in suspected disease cases. In this study, we developed a multiplex reverse transcriptase PCR to detect these viruses using a novel dual-priming oligonucleotide (DPO). The DPO contains two separate priming regions joined by a polydeoxyinosine linker, which blocks extension of nonspecifically primed templates and consistently allows high PCR specificity even under less-than-optimal PCR conditions. A total of 19 DPO primers were designed to detect and discriminate between RVFV, BTV, RPV, and PPRV by the generation of 205-, 440-, 115-, and 243-bp cDNA products, respectively. The multiplex reverse transcriptase PCR described here enables the early diagnosis of these four viruses and may also be useful as part of a testing regime for cattle, sheep, or goats exhibiting similar clinical signs, including mucosal lesions.

Prevalence of antibodies to phleboviruses and flaviviruses in Peja, Kosovo

In order to investigate the current and past activity of phlebovirus and flavivirus in Kosovo, a seroprevalence study among 200 blood donors was performed. Positive results were obtained for the phleboviruses TOSV and SFNV, and for a flavivirus of the Japanese Encephalitis group. No positive results for TBEV were observed.

West Nile virus and its emergence in the United States of America

Zoonotic West Nile virus (WNV) circulates in natural transmission cycles involving certain mosquitoes and birds, horses, humans, and a range of other vertebrates are incidental hosts. Clinical infections in humans can range in severity from uncomplicated WNV fever to fatal meningoencephalitis. Since its introduction to the Western Hemisphere in 1999, WNV had spread across North America, Central and South America and the Caribbean, although the vast majority of severe human cases have occurred in the United States of America (USA) and Canada. By 2002-2003, the WNV outbreaks have involved thousands of patients causing severe neurologic disease (meningoencephalitis and poliomyelitis-like syndrome) and hundreds of associated fatalities in USA. The purpose of this review is to present recent information on the epidemiology and pathogenicity of WNV since its emergence in North America.

Pathogenicity of two recent Western Mediterranean West Nile virus isolates in a wild bird species indigenous to Southern Europe: the red-legged partridge

West Nile virus (WNV) is an emerging zoonotic pathogen whose geographic spread and incidence in humans, horses and birds has increased significantly in recent years. WNV has long been considered a mild pathogen causing self-limiting outbreaks. This notion has changed as WNV is causing large epidemics with a high impact on human and animal health. This has been particularly noteworthy since its introduction into North America in 1999. There, native bird species have been shown to be highly susceptible to WNV infection and disease with high mortalities. For this reason, the effect of WNV infection in North American bird species has been thoroughly studied by means of experimental inoculations in controlled trials. To a lesser extent, European wild birds have been shown to be affected clinically by WNV infection. Yet experimental studies on European wild bird species are lacking. The red-legged partridge (Alectoris rufa) is a gallinaceous bird indigenous to the Iberian Peninsula, widely distributed in South Western Europe. It plays a key role in the Mediterranean ecosystem and constitutes an economically important game species. As such it is raised intensively in outdoor facilities. In this work, red-legged partridges were experimentally infected with two recent WNV isolates from the Western Mediterranean area: Morocco/2003 and Spain/2007. All inoculated birds became viremic and showed clinical disease, with mortality rates of 70% and 30%, respectively. These results show that Western Mediterranean WNV variants can be pathogenic for some European bird species, such as the red-legged partridge.

Mosquito surveys and West Nile virus screening in two different areas of southern Portugal, 2004-2007

Longitudinal mosquito surveys were carried out in southern Portugal from 2004 to 2007, in a wetland area (Comporta, District of Setúbal) and around the perimeter of a dam irrigation plant that created the largest artificial lake in Europe, 250 km(2) (Alqueva, Districts of Evora and Beja). Our aim was to study the diversity, abundance, and seasonal dynamics of mosquitoes, comparing these two different areas, to screen mosquitoes for West Nile Virus (WNV), an arboviral agent already detected in Portugal, because these areas are populated with abundant avian fauna. Monthly collections of adult mosquitoes were carried out by Centers for Disease Control light-traps with CO(2) and by indoor resting collections. Mosquitoes were identified and screened for arboviruses by reverse transcriptase (RT)-polymerase chain reaction directed toward amplification of a 217-bp fragment of the NS5 gene. Mosquito peak densities were observed in July-August in Comporta and May-June, with a plateau in July-October, in Alqueva. However, densities were far higher in Comporta area (220,821 specimens) than in Alqueva area (9442 specimens), with a clear difference in species distribution, as in Comporta the predominant species was Culex theileri (85%), followed by Aedes caspius (6%), Anopheles atroparvus (4%), and Culex pipiens sensu latu (s.l.) (3%), whereas in Alqueva the predominant species was Cx. pipiens s.l. (56%), followed by An. atroparvus (18%), Cx. theileri (14%), and Culiseta longiareolata (9%). Female mosquitoes (8842 in 175 pools) of the species Ae. caspius, An. atroparvus, Culex mimeticus, Cx. pipiens Sensu latu (s.l.), Cx. theileri, and Culex univittatus were screened and found to be negative for WNV genomic RNA. Although there was no detection of WNV sequences in mosquitoes, vigilance should continue as the circulation of virus has been previously detected more than once in Portugal, in humans, animals, and mosquitoes, and in other surrounding Mediterranean countries.

Assessment of a novel real-time pan-flavivirus RT-polymerase chain reaction

Outbreaks of West Nile virus (WNV) have occurred intermittently in regions around the Mediterranean coast, and the virus may have become established in Northern Italy and Romania, with reported intermittent outbreaks in Spain, Hungary, and France. WNV has also spread rapidly throughout the Americas since its introduction into New York in 1999. This capacity to emerge in new geographical locations and to spread rapidly together with the current increase in incidence of other flaviviruses such as tick-borne encephalitis virus, dengue virus, and Usutu virus has prompted us to design a novel pan-flavivirus RT-polymerase chain reaction for the purpose of surveillance for a range of flaviviruses. The assay utilizes degenerate primers targeting the flavivirus NS5 gene (RNA-dependent RNA polymerase) and detects a range of flaviviruses, including WNV. A small panel of WNV bird samples obtained from the United States has been shown to be detected using this assay. The amplicon generated is of sufficient size to provide sequence data to confirm the identity of the virus detected and undertake limited phylogenetic analysis. Testing using this assay has shown its ability to detect a range of tick-borne flaviviruses, particularly louping ill virus that is endemic in areas of the United Kingdom. The assay has been used to survey 160 bird samples and 1000 mosquito samples from the United Kingdom and found no evidence for WNV.

[Sero-epidemiological study of West Nile virus circulation in human in Tunisia]

West Nile virus (WNV) is an arbovirus classified into the family of Flaviviridae, genus Flavivirus. It is responsible for neurological diseases that occurred frequently as outbreaks and considered as an emerging infection in different regions of the world. In Tunisia, two outbreaks of meningoencephalitis due to this virus occurred, in 1997 and 2003. The virus circulation is studied only in Sahel, region affected by the two epidemics. The aim of this study is to determine if WNV is present in other regions of the country where, up to now, no data are available. A total of 1,854 sera collected from healthy patients were investigated by ELISA to detect specific IgG, during January to December 2007. Patients included are from three governorates: Kairouan, Bizerte, and Sfax. The governorate of Sfax (center of Tunisia) was affected by the two outbreaks, whereas only two cases were observed previously at Kairouan and no cases at Bizerte. Specific IgG were detected in 12.5% of studied population. This seroprevalence varied largely between the three governorates studied. Globally, three regions with different endemicity were described: high endemicity at Kairouan (27.7%), moderate at Sfax (7.5%), and low at Bizerte (0.7%). At Kairouan, the seroprevalence is significantly higher in individuals aged over 40. Our results suggest that WNV circulates in Tunisia; it has a high risk not only in regions affected by previous outbreaks but throughout the country. An active surveillance should be instituted in the country. It must target individuals, and animals, which can be vectors or reservoirs for the virus.

Fast duplex one-step reverse transcriptase PCR for rapid differential detection of West Nile and Japanese encephalitis viruses

The aim of this study was to develop a highly sensitive and specific one-step duplex reverse transcriptase PCR (RT-PCR) assay for the simultaneous and differential detection of West Nile (WNV) and Japanese encephalitis (JEV) viruses. The bioinformatic analysis of published sequences of WNV and JEV revealed conserved regions not targeted by previously reported primers. A total of 13 primers were designed based on these regions to detect all of the WNV and JEV lineages and to discriminate between the two viruses by the generation of 482- and 241-bp cDNA products, respectively. The results indicate that single-tube duplex PCR using these primers is a useful technique for the detection and differentiation of WNV and JEV in plasma or brain tissue. The novel duplex RT-PCR described in this study enables the early diagnosis of these two encephalitic flaviviruses. In addition, this technique may be useful as part of a testing regimen for human patients, horses, and other susceptible animal species, as it is rapid (less than 3.5 h from RNA extraction), sensitive, and specific, and it may enable the differential diagnosis of clinical samples.

Malaria risk in Corsica, former hot spot of malaria in France

Background

The prevalence of Plasmodium falciparum and Plasmodium vivax malaria was very high in Corsica just before the Second World War. The last outbreak was in 1972 and the most recent indigenous case was in 2006.

Results

Analysis of historical data shows that anopheline vectors were abundant. Recent surveys demonstrated that potential vectors are still present in Corsica, despite the likely disappearance of Anopheles sacharovi. Moreover, P. falciparum can develop experimentally into these mosquitoes, notably Anopheles labranchiae, which is locally abundant, and parasites are regularly introduced into the island.

Discussion, Conclusions

The presence of vectors, the introduction of parasites and the conducive climate raise questions about the possibility of malaria re-emerging and becoming re-established in Corsica. Analysis of historic and current parasitological and entomological data shows that the current theoretical risk of indigenous cases or malaria foci is negligible, particularly since there is very little contact between humans and Anopheles mosquitoes, Plasmodium carriers are reliably treated and there is a widespread vector control on the island.

Small molecule drug discovery for Dengue and West Nile viruses: applying experience from hepatitis C virus

There are currently no specific treatments for infection with Dengue virus (DENV) and West Nile Virus (WNV). Drug-discovery programs are underway for both viruses, but as yet no small molecules have advanced to clinical trials. Hepatitis C virus (HCV) is a related flavivirus that has been the focus of intense drug discovery efforts for the last two decades. Many approaches currently being pursued for DENV and WNV have been previously attempted for HCV with varying degrees of success. The experience with HCV may direct DENV and WNV efforts towards approaches with the best chance of success. Based on experience with HCV, the viral polymerase and protease are attractive targets to focus on since these have been most successful to date. Cell-based phenotypic screening may also yield attractive inhibitors. The helicase and methyltransferase enzymes are likely to prove difficult targets and host target approaches are fraught with safety concerns.

Transcriptome changes in Culex quinquefasciatus (Diptera: Culicidae) salivary glands during West Nile virus infection

Persistent West Nile virus (WNV) infection in the mosquito Culex quinquefasciatus Say (Diptera: Culicidae) is associated with pathological changes in the salivary glands, including apoptotic cell death and a corresponding reduction in virus transmission over time. The vector host response to WNV infection and the molecular basis of WNV pathogenesis in Cx. quinquefasciatus was investigated using oligonucleotide microarrays designed to detect differences in the salivary gland transcriptome between WNV-infected mosquitoes and uninfected controls. Transcripts with increased abundance in infected salivary glands included those related to immunity, transcription, protein transport and degradation, amino acid and nucleotide metabolism, signal transduction, and cellular detoxification. Microarray-based analysis detected a decrease in transcript levels of a Culex inhibitor of apoptosis gene (IAP-1) and a decrease in abundance of 11 transcripts encoding salivary gland proteins. Transcript levels for an endonuclease, a proline-rich mucin, and several D7 protein family members also decreased. Transcripts with the greatest change in abundance during infection had either no similarity to sequences found in GenBank, VectorBase, and FlyBase, or were similar to sequences with uncharacterized protein products. These transcripts represent exciting targets for future analysis. Results from this study suggest that WNV infection influences transcriptional changes in an invertebrate host target tissue that may confer an advantage to the replicating virus, induce a host defense response, and alter the composition of vector saliva. The ramifications of these changes are discussed in terms of mosquito vector competence and WNV pathogenesis.

West nile virus: characteristics of an african virus adapting to the third millennium world

The emergence and spread of West Nile Virus (WNV) from North through South America during the last decade, and the recent outbreaks of disease in both humans and horses in Europe suggest that the epidemiology of this infection is evolving. WNV is now considered among the emerging threats for both human and veterinary public health in areas like Europe where it was previously regarded to as an exotic agent. Further knowledge has built up from studies investigating the characteristics of the virus and its genome evolution capacity, the adaptation to new avian host species, the changes in vector competence and biology, and the host-pathogen interactions, including the immune response. Also, the new needs for preparedness to future major outbursts of disease have stimulated research on virus detection and characterization, filling the gaps in both specialized diagnostic technology and the need for field rapid assays. This review will present an overview of WNV virology, remarking the impact of virus diversity and evolution on theoretical and practical aspects involved in both risk definition, detection and control of infection.

On the effect of diagnostic misclassification bias on the observed spatial pattern in regional count data--a case study using West Nile virus mortality data from Ontario, 2005

Geographic epidemiology is concerned with the investigation of spatially referenced data to discover spatial patterns in the health status of populations. In this context it is generally assumed that a perfect diagnostic test is used to classify individuals as being positive or negative, meaning the health status is measured without error. In this work the effect of an imperfect diagnostic test on spatial patterns of disease in regional count data is investigated in a case study. Specifically the misclassification effect on the semivariogram, Moran's I statistic and the spatial scan test are evaluated for the situation of West Nile virus infections among dead birds sampled from the 30 public health units of southern Ontario in 2005. We illustrate that under large sample conditions no serious spatial bias is introduced by use of an imperfect diagnostic test as long as the imperfection itself is spatially unbiased.

Environmental risk factors of West Nile virus infection of horses in the Senegal River basin

In 2005, a serological study was carried out on horses in five ecologically contrasted zones of the Senegal River basin (Senegal) to assess West Nile virus (WNV) transmission and investigate underlying environmental risk factors. In each study zone, horses were randomly selected and blood samples taken. A land-cover map of the five study areas was built using two satellite ETM+ images. Blood samples were screened by ELISA for anti-WNV IgM and IgG and positive samples were confirmed by seroneutralization. Environmental data were analysed using a principal components analysis. The overall IgG seroprevalence rate was 85% (n=367; 95% CI 0.81-0.89). The proximity to sea water, flooded banks and salted mudflats were identified as protective factors. These environmental components are unfavourable to the presence of Culex mosquitoes suggesting that in Senegal, the distribution of the vector species is more limiting for WNV transmission than for the hosts' distribution.

Evaluation of an enzyme-linked immunosorbent assay for detection of West Nile virus infection based on a recombinant envelope protein produced in Trichoplusia ni larvae

West Nile virus (WNV), a Flavivirus distributed most widely, is presenting lately variable epidemiological and ecological patterns, including an increasing virulence that has already caused over 1000 human deaths in USA. Currently, diagnosis of WNV is achieved mainly by enzyme-linked immunoassays (ELISAs) based on the use of inactivated whole WNV (iWNV) as antigen, although results have to be confirmed by plaque reduction neutralization tests (PRNTs). Expression of WNV envelope recombinant E (rE) protein and its usefulness as ELISA antigen are described. Production of rE was achieved upon infection of Trichoplusia ni insect larvae with a recombinant baculovirus. Once optimized, the rE-based ELISA was validated with a battery of mouse and equine sera characterized previously. Concordance with the iWNV-based ELISA used routinely was good (95%), as it was with the reference PRNT (90%), with specificity of 94.4% and sensitivity of 88.1%. Production of rE protein in insect larvae allows for an easy, low cost and quite large-scale yield of partially purified antigen which is suitable for serological diagnosis of WNV, without the need for manipulation of large quantities of infective virus.

West Nile virus antibodies in wild birds, Morocco, 2008

To determine circulation of West Nile virus (WNV) during nonepidemic times, we serosurveyed wild birds of Morocco in 2008. We found antibodies against WNV in 12 (3.5%) birds, against Usutu virus in 1 (0.3%), and against both in 2 (0.6%). High WNV prevalence among juvenile birds suggests local virus circulation among resident birds.

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

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

Characterization of West Nile virus isolates from Spain: new insights into the distinct West Nile virus eco-epidemiology in the Western Mediterranean

West Nile virus (WNV) is a mosquito-borne flavivirus which causes important morbidity and mortality in birds, horses and humans. In the Western Mediterranean region, WNV causes sporadic, self-limited outbreaks, with few or no human cases. Here we report the characterization of two recent Western Mediterranean WNV isolates, obtained in Spain in 2007 from two golden eagles. Complete genome sequence comparisons revealed high identity between these isolates and close relationship with other Western Mediterranean WNV strains isolated since 1996. Phylogenetic analysis within this group indicated that two distinct phylogenetic groups have emerged from earlier strains. Pathogenicity analysis in mice showed that the Spanish isolate is less pathogenic than other strains either from the Western Mediterranean (Morocco 2003) or from North America (NY'99). Changes in amino acid position NS3-249 (claimed as a virulence marker) did not influence the pathogenicity observed.

Searching for West Nile virus (WNV) in Greece

West Nile virus (WNV), a mosquito-borne flavivirus, has increasingly become a concern in both America and Europe due to its complex and unpredictable lifecycle. Transfusion-associated transmission of the WNV has been well documented during the last few years. This study aimed to detect the presence of WNV in: (i) cerebrospinal fluid (CSF) specimens derived from aseptic meningitis cases in Greece and (ii) Greek blood donations. A total of 115 CSF specimens from patients suffering from aseptic meningitis and 9590 blood samples were collected from seven Greek hospitals during the periods June to October 2006 and 2007 and tested for investigational purposes. Both blood and CSF samples were tested for the presence of WNV RNA by using the PROCLEIX WNV assay. None of 115 CSF and 9590 blood donor samples was found positive according to our testing algorithms. Despite the presence of WNV in Balkan countries, WNV has not reached significant levels in Greece.

Selective involvement of temporal regions in a case of flavivirus encephalitis

Clinical manifestations of flavivirus infection may be various, from unapparent to severe meningoencephalitis. Our patient, 2 weeks after returning home from a holiday at Elba Island, developed biphasic fever, later associated with nausea and vomiting and followed by incoming seizures responsive to thiopental sodium only. Brain MRI showed bilateral hyperintensity (T2) in amygdale, hippocampus, left insular and temporal inferior cortex. Standard and microbiological CSF examination was normal, but microbiological serum analysis showed seroconversion for flavivirus. The patient came to our observation 6 months after disease onset and at that time he was affected by frequent seizures and severe cognitive impairment with behavioural disturbances; the patient also showed distal weakness with footstepping. EEG showed bitemporal epileptic foci. During the following months, seizures greatly decreased and cognitive status improved in response to a complex antiepileptic therapy. Flavivirus encephalitis should be taken into account in the differential diagnosis of encephalitis selectively involving temporal lobes.

Simultaneous detection and quantitation of Chikungunya, dengue and West Nile viruses by multiplex RT-PCR assays and dengue virus typing using high resolution melting

Chikungunya (CHIKV), Dengue (DENV) and West Nile (WNV) viruses are arthropod-borne viruses that are able to emerge or re-emerge in many regions due to climatic changes and increase in travel. Since these viruses produce similar clinical signs it is important for physicians and epidemiologists to differentiate them rapidly. A molecular method was developed for their detection and quantitation in plasma samples and a DENV typing technique were developed. The method consisted in performing two multiplex real-time one-step RT-PCR assays, to detect and quantify the three viruses. Both assays were conducted in a single run, from a single RNA extract containing a unique coextracted and coamplified composite internal control. The quantitation results were close to the best detection thresholds obtained with simplex RT-PCR techniques. The differentiation of DENV types was performed using a High Resolution Melting technique. The assays enable the early diagnosis of the three arboviruses during viremia, including cases of coinfection. The method is rapid, specific and highly sensitive with a potential for clinical diagnosis and epidemiological surveillance. A DENV positive sample can be typed conveniently using the High Resolution Melting technique using the same apparatus.