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West Nile virus
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Epidemiology of human West Nile virus infections in the European Union and European Union enlargement countries, 2010 to 2018
More LessBackgroundWest Nile virus (WNV) circulates in an enzootic cycle involving mosquitoes and birds; humans are accidental hosts.
AimWe analysed human WNV infections reported between 2010 and 2018 to the European Centre for Disease Prevention and Control to better understand WNV epidemiology.
MethodsWe describe probable and confirmed autochthonous human cases of WNV infection reported by European Union (EU) and EU enlargement countries. Cases with unknown clinical manifestation or with unknown place of infection at NUTS 3 or GAUL 1 level were excluded from analysis.
ResultsFrom southern, eastern and western Europe, 3,849 WNV human infections and 379 deaths were reported. Most cases occurred between June and October. Two large outbreaks occurred, in 2010 (n = 391) and in 2018 (n = 1,993). The outbreak in 2018 was larger than in all previous years and the first cases were reported unusually early. The number of newly affected areas (n = 45) was higher in 2018 than in previous years suggesting wider spread of WNV.
ConclusionReal-time surveillance of WNV infections is key to ensuring that clinicians and public health authorities receive early warning about the occurrence of cases and potential unusual seasonal patterns. Human cases may appear shortly after first detection of animal cases. Therefore, public health authorities should develop preparedness plans before the occurrence of human or animal WNV infections.
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Mosquito surveillance of West Nile and Usutu viruses in four territorial units of Slovakia and description of a confirmed autochthonous human case of West Nile fever, 2018 to 2019
More LessBackgroundDespite the known circulation of West Nile virus (WNV) and Usutu virus (USUV) in Slovakia, no formal entomological surveillance programme has been established there thus far.
AimTo conduct contemporaneous surveillance of WNV and USUV in different areas of Slovakia and to assess the geographical spread of these viruses through mosquito vectors. The first autochthonous human WNV infection in the country is also described.
MethodsMosquitoes were trapped in four Slovak territorial units in 2018 and 2019. Species were characterised morphologically and mosquito pools screened for WNV and USUV by real-time reverse-transcription PCRs. In pools with any of the two viruses detected, presence of pipiens complex group mosquitoes was verified using molecular approaches.
ResultsAltogether, 421 pools containing in total 4,508 mosquitoes were screened. Three pools tested positive for WNV and 16 for USUV. USUV was more prevalent than WNV, with a broader spectrum of vectors and was detected over a longer period (June–October vs August for WNV). The main vectors of both viruses were Culex pipiens sensu lato. Importantly, WNV and USUV were identified in a highly urbanised area of Bratislava city, Slovakias’ capital city. Moreover, in early September 2019, a patient, who had been bitten by mosquitoes in south-western Slovakia and who had not travelled abroad, was laboratory-confirmed with WNV infection.
ConclusionThe entomological survey results and case report increase current understanding of the WNV and USUV situation in Slovakia. They underline the importance of vector surveillance to assess public health risks posed by these viruses.
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Unprecedented increase of West Nile virus neuroinvasive disease, Spain, summer 2020
More LessLucía García San Miguel Rodríguez-Alarcón , Beatriz Fernández-Martínez , María José Sierra Moros , Ana Vázquez , Paula Julián Pachés , Elena García Villacieros , María Belén Gómez Martín , Jordi Figuerola Borras , Nicola Lorusso , Julian Mauro Ramos Aceitero , Elena Moro , Aránzazu de Celis , Salvador Oyonarte , Beatriz Mahillo , Luis José Romero González , María Paz Sánchez-Seco , Berta Suárez Rodríguez , Ulises Ameyugo Catalán , Santiago Ruiz Contreras , Mayte Pérez-Olmeda and , Fernando Simón SoriaCases of West Nile neuroinvasive disease (WNND) in Spain increased in summer 2020. Here we report on this increase and the local, regional and national public health measures taken in response. We analysed data from regional surveillance networks and the National Epidemiological Surveillance Network, both for human and animal West Nile virus (WNV) infection. During the 2020 season, a total of 77 human cases of WNV infection (median age 65 years; 60% males) were detected in the south-west of Spain; 72 (94%) of these cases developed WNND, presenting as meningoencephalitis, seven of which were fatal. In the previous two decades, only six human cases of WNND were detected in Spain. Reduced activities for vector control this season, together with other factors, might have contributed to the massive increase. Public health measures including vector control, campaigns to raise awareness among physicians and the general population, and interventions to ensure the safety of donations of blood products, organs, cells and tissues were effective to reduce transmission. Going forward, maintenance of vector control activities and an update of the vector-borne diseases response plan in Spain is needed.
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Autochthonous West Nile virus infection outbreak in humans, Leipzig, Germany, August to September 2020
More LessFollowing a distinct summer heat wave, nine autochthonous cases of West Nile fever and West Nile neuroinvasive disease, including one fatality, were observed in Leipzig, Germany, in August and September 2020. Phylogenetic analysis demonstrated close relationships in viruses from humans, animals and mosquitos in eastern Germany, obtained during the preceding 2 years. The described large cluster of autochthonous West Nile virus infections in Germany indicates endemic seasonal circulation of lineage 2 viruses in the area.
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Characterising West Nile virus epidemiology in Israel using a transmission suitability index
More LessBackgroundClimate is a major factor in the epidemiology of West Nile virus (WNV), a pathogen increasingly pervasive worldwide. Cases increased during 2018 in Israel, the United States and Europe.
AimWe set to retrospectively understand the spatial and temporal determinants of WNV transmission in Israel, as a case study for the possible effects of climate on virus spread.
MethodsWe employed a suitability index to WNV, parameterising it with prior knowledge pertaining to a bird reservoir and Culex species, using local time series of temperature and humidity as inputs. The predicted suitability index was compared with confirmed WNV cases in Israel (2016–2018).
ResultsThe suitability index was highly associated with WNV cases in Israel, with correlation coefficients of 0.91 (p value = 4 × 10− 5), 0.68 (p = 0.016) and 0.9 (p = 2 × 10− 4) in 2016, 2017 and 2018, respectively. The fluctuations in the number of WNV cases between the years were explained by higher area under the index curve. A new WNV seasonal mode was identified in the south-east of Israel, along the Great Rift Valley, characterised by two yearly peaks (spring and autumn), distinct from the already known single summer peak in the rest of Israel.
ConclusionsBy producing a detailed geotemporal estimate of transmission potential and its determinants in Israel, our study promotes a better understanding of WNV epidemiology and has the potential to inform future public health responses. The proposed approach further provides opportunities for retrospective and prospective mechanistic modelling of WNV epidemiology and its associated climatic drivers.
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First autochthonous human West Nile virus infections in the Netherlands, July to August 2020
More LessIn October 2020, the first case of autochthonous West Nile virus neuroinvasive disease was diagnosed in the Netherlands with a presumed infection in the last week of August. Investigations revealed five more cases of local West Nile virus (WNV) infection. The cases resided in a region where WNV was detected in a bird and mosquitoes in August 2020. Molecular analysis was successful for two cases and identified the presence of WNV lineage 2.
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Detection of West Nile virus in a common whitethroat (Curruca communis) and Culex mosquitoes in the Netherlands, 2020
More LessReina S Sikkema , Maarten Schrama , Tijs van den Berg , Jolien Morren , Emmanuelle Munger , Louie Krol , Jordy G van der Beek , Rody Blom , Irina Chestakova , Anne van der Linden , Marjan Boter , Tjomme van Mastrigt , Richard Molenkamp , Constantianus JM Koenraadt , Judith MA van den Brand , Bas B Oude Munnink , Marion PG Koopmans and Henk van der JeugdOn 22 August, a common whitethroat in the Netherlands tested positive for West Nile virus lineage 2. The same bird had tested negative in spring. Subsequent testing of Culex mosquitoes collected in August and early September in the same location generated two of 44 positive mosquito pools, providing first evidence for enzootic transmission in the Netherlands. Sequences generated from the positive mosquito pools clustered with sequences that originate from Germany, Austria and the Czech Republic.
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West Nile virus in humans, Greece, 2018: the largest seasonal number of cases, 9 years after its emergence in the country
More LessDanai Pervanidou , Annita Vakali , Theano Georgakopoulou , Takis Panagiotopoulos , Eleni Patsoula , George Koliopoulos , Constantina Politis , Kostas Stamoulis , Elpida Gavana , Styliani Pappa , Maria Mavrouli , Maria Emmanouil , George Sourvinos , Andreas Mentis , Athanassios Tsakris , Christos Hadjichristodoulou , Sotirios Tsiodras and Anna PapaBackgroundHuman cases of West Nile virus (WNV) infection are recorded since 2010 in Greece, with seasonal outbreaks occurring almost annually. Enhanced surveillance has been implemented since 2010, to promptly characterise cases’ temporal and geographical distribution and inform authorities for implementation of appropriate measures (mosquito control, health education, blood safety).
AimWe describe the epidemiology of WNV human infections in Greece focusing on the 2018 season.
MethodsThe National Public Health Organization advised physicians to test all suspect WNV infection cases and refer samples to reference laboratories. Laboratories notified diagnosed cases on a daily basis. Treating physicians, patients, and infected blood donors were interviewed within 48 hours after diagnosis and the probable infection location was identified. Hospitalised cases were followed up until discharge.
ResultsA total of 317 autochthonous WNV infection cases were diagnosed in 2018. Among them, 243 cases had neuroinvasive disease (WNND), representing a 23% increase of WNND cases compared with 2010, the previous most intense season. There were 51 deaths. Cases started occurring from week 22, earlier than usual. Both rural and urban areas were affected, with 86 (26% of the total) municipalities belonging to seven (54% of the total) regions recording cases. Two major epicentres were identified in Attica and Central Macedonia regions.
ConclusionsThe largest number of human cases of WNV infection ever recorded in Greece occurred in 2018, with a wide geographical distribution, suggesting intense virus circulation. Enhanced surveillance is vital for the early detection of human cases and the prompt implementation of response measures.
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Toscana, West Nile, Usutu and tick-borne encephalitis viruses: external quality assessment for molecular detection of emerging neurotropic viruses in Europe, 2017
More LessBackgroundNeurotropic arboviruses are increasingly recognised as causative agents of neurological disease in Europe but underdiagnosis is still suspected. Capability for accurate diagnosis is a prerequisite for adequate clinical and public health response.
AimTo improve diagnostic capability in EVD-LabNet laboratories, we organised an external quality assessment (EQA) focusing on molecular detection of Toscana (TOSV), Usutu (USUV), West Nile (WNV) and tick-borne encephalitis viruses (TBEV).
MethodsSixty-nine laboratories were invited. The EQA panel included two WNV RNA-positive samples (lineages 1 and 2), two TOSV RNA-positive samples (lineages A and B), one TBEV RNA-positive sample (Western subtype), one USUV RNA-positive sample and four negative samples. The EQA focused on overall capability rather than sensitivity of the used techniques. Only detection of one, clinically relevant, concentration per virus species and lineage was assessed.
ResultsThe final EQA analysis included 51 laboratories from 35 countries; 44 of these laboratories were from 28 of 31 countries in the European Union/European Economic Area (EU/EEA). USUV diagnostic capability was lowest (28 laboratories in 18 countries), WNV detection capacity was highest (48 laboratories in 32 countries). Twenty-five laboratories were able to test the whole EQA panel, of which only 11 provided completely correct results. The highest scores were observed for WNV and TOSV (92%), followed by TBEV (86%) and USUV (75%).
ConclusionWe observed wide variety in extraction methods and RT-PCR tests, showing a profound absence of standardisation across European laboratories. Overall, the results were not satisfactory; capacity and capability need to be improved in 40 laboratories.
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Extraordinary increase in West Nile virus cases and first confirmed human Usutu virus infection in Hungary, 2018
More LessBackgroundDuring the 2018 WNV transmission season, similarly to other endemic areas in Europe, a large number of human West Nile virus (WNV) infections were reported in Hungary.
AimsWe summarise the epidemiological and laboratory findings of the 2018 transmission season and expand experiences in flavivirus differential diagnostics.
MethodsEvery patient with clinical suspicion of acute WNV infection was in parallel tested for WNV, tick-borne encephalitis virus and Usutu virus (USUV) by serological methods. Sera, whole blood and urine samples were also tested for the presence of viral nucleic acid.
ResultsUntil the end of December 2018, 215 locally acquired and 10 imported human WNV infections were notified in Hungary. All reported cases were symptomatic; most of them exhibited neurological symptoms. In a large proportion of tested individuals, whole blood was the most appropriate sample type for viral nucleic acid detection, but because whole blood samples were not always available, testing of urine samples also extended diagnostic possibilities. In addition, the first human USUV infection was confirmed in 2018 in a patient with aseptic meningitis. Serological cross-reactions with WNV in different serological assays were experienced, but subsequent molecular biological testing and sequence analysis identified Europe lineage 2 USUV infection.
ConclusionCareful interpretation and simultaneous application of different laboratory methods are necessary to avoid misdiagnosis of human USUV cases. Expansion of the laboratory-confirmed case definition criteria for detection of viral RNA in any clinical specimens to include urine samples could increase diagnostic sensitivity.
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West Nile virus infection in individuals with pre-existing Usutu virus immunity, northern Italy, 2018
More LessIn 2018, there was a large West Nile virus (WNV) outbreak in northern Italy. We observed five atypical cases of WNV infection that were characterised by the presence of WNV RNA and WNV IgG at the time of diagnosis, but no IgM response during follow-up. Neutralisation assays demonstrated pre-existing Usutu virus immunity in all patients. Besides challenging diagnosis, the immunological crosstalk between the two viruses warrants further investigation on possible cross-protection or infection enhancement effects.
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One Health approach for West Nile virus surveillance in the European Union: relevance of equine data for blood safety
More LessWest Nile virus (WNV) infection is notifiable in humans and equids in the European Union (EU). An area where a human case is detected is considered affected until the end of the mosquito transmission season (week 48) and blood safety measures have to be implemented. We used human and equine case notifications between 2013 and 2017 to define the WNV distribution in the EU and to investigate the relevance of using equine cases as a complementary trigger for blood safety measures. Adding areas with equine cases to the definition of an affected area would have a major impact on blood safety measures. Adding areas with equine cases where human cases have been reported in the past would increase the timeliness of blood safety measures with only a limited impact. Although the occurrence of human and/or equine cases confirms virus circulation in the EU, no evidence was found that occurrence of equine cases leads to human cases and vice versa. We conclude that information about equine data should contribute to raising awareness among public health experts and trigger enhanced surveillance. Further studies are required before extending the definition of affected areas to areas with human and/or equine cases.
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Epidemiologic and phylogenetic analysis of the 2018 West Nile virus (WNV) outbreak in Israel demonstrates human infection of WNV lineage I
More LessAs at 12 November 2018, an outbreak of West Nile virus (WNV) was responsible for 139 WNV infection cases in Israel. Here, we characterise the epidemiology of the outbreak and demonstrate that only WNV lineage I was circulating in mosquitoes and responsible for WNV infection in humans. This suggests that the concurrence of the outbreak in Israel with WNV outbreaks in several European countries is not due to a common, more virulent WNV genotype.
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