1. Please check and comment entries here.
Table of Contents

    Topic review

    Usutu virus in Europe

    Subjects: Virology
    View times: 250


    Usutu virus (USUV) is an emerging arbovirus isolated in 1959 (Usutu River, Swaziland). Previously restricted to sub-Saharan Africa, the virus was introduced in Europe in 1996. While USUV has received little attention in Africa, the virus emergence has prompted numerous studies with robust epidemiological surveillance programs in Europe. Epizootics and genetic diversity of USUV in different bird species as well as detection of the virus in mosquitoes suggest repeated USUV introductions into Europe with endemization in some countries. The zoonotic potential of USUV has been reported in a growing number of human cases. Clinical cases of neuroinvasive disease and USUV fever, as well as seroconversion in blood donors were reported in Europe since 2009. Since spreading trends of USUV are likely to continue, continuous multidisciplinary interventions ('One Health' concept) should be conducted for monitoring and prevention of this emerging arboviral infection.

    1. Introduction

    Usutu virus (USUV) is an emerging arbovirus that belongs to the family Flaviviridae, genus Flavivirus, Japanese encephalitis serocomplex. Similar to other flaviviruses, USUV is a spherical, small, enveloped virus with a single stranded positive-sense RNA genome of ~12 kb. Phylogenetic analyses of the NS5 gene have shown that USUV strains clustered into eight genetic lineages: three African (Africa 1–3) and five European (Europe 1–5) [1]. In nature, USUV is maintained in a bird–mosquito–bird cycle, however the virus or antibodies detection were reported sporadically in humans, horses and other mammals (Figure 1).

    USUV was isolated in 1959 from Culex neavei mosquito caught near the Usutu River in Swaziland [2]. After that, the virus was confined to Africa with only few human cases with fever, rash and jaundice reported [3]. In Africa, the USUV host range includes mosquitoes, birds, equids and dogs [4][5]. The virus was also isolated and nucleotide sequenced from five asymptomatic small mammals in Senegal that belong to two rodent species (black rat; Rattus rattus and multimammate rat; Mastomys natalensis) and a single species of shrew (Crocidura sp.) (Figure 1) [6].

    A retrospective analysis of archived tissue samples originating from a bird die-off showed that USUV emerged in Europe in 1996 (Tuscany region, Italy), five years before the advent of USUV-associated bird deaths in Austria which has been generally assumed as the starting point of the virus spread in Europe [7]. In 2001, the virus caused the first large outbreak in several bird species in the region of Vienna (Austria) [8]. In the following years, continuous geographic expansion of the USUV in Europe has been shown by reports of epizootics or small outbreaks as well as serologic detection in different wild and captive bird species [9][10][11][12]. In addition, the virus was detected in different native (mainly Culex pipiens) and invasive mosquito species (Aedes albopictus, Ae. japonicus) [13][14][15][16][17][18]. USUV RNA was also found in bats (Pipistrellus pipistrellus) in Germany and Belgium [19][20]. Moreover, USUV antibodies were sporadically detected in horses [21][22][23], dogs [24], squirrels [25], wild boar, roe deer [26] and lizards [27] (Figure 1), expanding the USUV host range (Figure 1), however these species are considered incidental hosts.

    Figure 1. Usutu virus (USUV) transmission cycle involves birds (amplifying hosts) and mosquitoes (vectors). Infection can be transmitted to humans and horses which are generally considered incidental or “dead-end” hosts. USUV isolation/detection (black symbols) and serologic evidence (blue symbols) were reported in different animal species, expanding the incidental host range.

    The zoonotic potential of USUV has been reported in a limited number of human cases. Few cases of neuroinvasive disease and USUV fever, as well as seroconversion in blood donors were reported in Europe since 2009 [11][28][29][30][31][32][33]. Phylogenetic analyses showed that the majority of USUV strains detected in humans, birds and mosquitoes belong to European USUV lineages, however several reports indicated the presence of African lineages as well [18][34][35][36].

    The USUV diversity in Europe appeared in the last decade, however, the phylogenies suggest a long-term virus circulation in this region [37]. The presence of USUV was documented by virus isolation/detection or serologically in Austria, Belgium, Croatia, the Czech Republic, France, Germany, Greece, Hungary, Italy, the Netherlands, Poland, Serbia, Slovakia, Spain, Switzerland and the United Kingdom.

    The emergence and geographic distribution of USUV infections in European countries is presented in Table 1 and Figure 2.

    Table 1. Emergence of Usutu virus (USUV) in Europe: clinical cases/seroconversion/RNA detection/serologic evidence. In Europe, USUV emerged in 1996 in the Tuscany region (Italy) when it was detected by retrospective analysis of archived tissues from dead birds. In mosquitoes, USUV was discovered for the first time in 2006 (Spain) in a pool of Cx. pipiens. Seroconversion in horses was reported in 2008 (Italy), following the first two human clinical cases in 2009. In 2013, the virus was detected in two dead bats (Pipistrellus pipistrellus) in Germany. Until 2018, USUV infections were reported in 16 European countries.

    Country Pathogens 09 00699 i001 Pathogens 09 00699 i002 Pathogens 09 00699 i003 Pathogens 09 00699 i004 Pathogens 09 00699 i005 Reference
    Austria 2016* 2001   2017   [8][17][37][38][39]
    Belgium   2012   2016 2017 [1][20][40]
    Croatia 2012 2018 2011 2016   [15][22][30][32]
    Czech Republic   2004   2013   [41][42]
    France 2016 2015   2015   [31][43][44]
    Germany 2012* 2011   2010 2013 [9][13][19][45]
    Greece   2010       [46]
    Hungary 2018 2005       [34][47]
    Italy 2009 1996 2008 2009   [7][21][28][29][48]
    Netherlands   2016       [49]
    Poland   2006 2012     [50][51]
    Serbia 2015 2012 2009 2014   [52][53][54]
    Slovakia   2010       [23][55]
    Spain   2011 2011 2006   [56][57][58][59]
    Switzerland   2006       [60]
    United Kingdom   2001       [61]
    Pathogens 09 00699 i006Clinical cases/RNA detection/seroconversion; Pathogens 09 00699 i007serologic evidence; *asymptomatic blood donors/blood donations.


    Figure 2. Geographic distribution of Usutu virus in Europe (clinical cases/RNA detection/seroconversion/serologic evidence).

    2. Conclusion

    Circulation of different European and African USUV lineages (Table 2, Figure 3), suggests multiple introduction events to Europe from Africa. The Europe 2 lineage is the most commonly detected USUV lineage in the European countries [16][32][62][63]. The Europe 3 USUV lineage was predominantly circulating in Southern Belgium in 2017 and 2018 [20]. Recent studies from Germany [64] and the Netherlands [65] showed an increase in the USUV Africa 3 lineage detection during the same period. The genetic diversity of European lineages is most likely shaped by enzootic maintenance (in situ evolution) rather than by extensive migration, while African lineages are driven mostly by extensive migration and repeated introduction of viral variants from different geographic origins [37]. In addition to data from the published articles, the sequences retrieved from the GenBank suggest for certain European countries broader host range as well as USUV lineage diversity within a specific host.

    Table 2. Molecular epidemiology of Usutu virus (USUV) in Europe. USUV Europe 2 lineage is the most prevalent genetic lineage detected in birds, mosquitoes and humans. In birds, Europe lineage 1, 3-5 and Africa 2 and 3 lineages were detected as well. Europe 3 and 4 and Africa 2 and 3 lineages were detected in mosquitoes. In bats, only Europe 3 lineage was documented so far.                                                      

    Country Pathogens 09 00699 i008 Pathogens 09 00699 i009 Pathogens 09 00699 i010 Pathogens 09 00699 i011 Reference
    Austria Europe 2*
    Africa 3*
    Europe 1,2
    Africa 3
    Europe 2**   [34][35][64][66]
    Belgium   Europe 1,3
    Africa 3
    Europe 3 Europe 3 [20][36][64][66]
    Croatia Europe 2 Europe 2 Europe 2   [32]
    Czech Republic   Europe 1,2,3
    Africa 3
    Europe 2   [18][42]
    France Africa 2 Europe 3 Europe 2
    Africa 2,3
    Germany Europe 3 Europe 2,3,5
    Africa 2,3
    Africa 3-like
    Europe 3
    Africa 3
    Europe 3 [9][19][64][67][68][69]
    Hungary Europe 2 Europe 1,2     [34][39][47][70]
    Italy Europe 1,2*,3*,4* Europe 2,4 Europe 2,4   [16][29][64][71][72]
    Netherlands Europe 3 Europe 3
    Africa 3
    Serbia     Europe 1,2   [75][76]
    Slovakia     Europe 2   [55]
    Spain   Africa 2 Africa 2   [1][77]
    Switzerland   Europe 1     [60]
    *Blood donors/donations; **based on nucleotide sequences retrieved from the GenBank.


    Figure 3. Neighbor-Joining tree of USUV sequences based on 495 nucleotides of the NS5 gen illustrating phylogenetic and host diversity of USUV strains detected in European countries. Taxon information includes the GenBank accession number, country in which the virus was detected, host and isolation/detection year. Colour codes for different hosts are shown in the upper left corner. USUV genetic lineages are indicated on the right. Scale bar indicates the mean number of nucleotide substitutions per site.

    The integrated veterinary and human surveillance system ('One Health') based on the viruses detection in mosquitoes, migratory and resident birds as well as horses and poultry was proved to be useful for estimating the public health risk for other flaviviruses such as WNV. This enables the effective and timely control of the diseases in humans [78][79][80]. Since spreading trends of USUV are likely to continue, continuous multidisciplinary interventions in accordance with the 'One Health' concept, should be conducted to increase the awareness of USUV and implement appropriate monitoring and prevention methods for this emerging arboviral infection.

    This entry is adapted from 10.3390/pathogens9090699


    1. Cadar, D.; Lühken, R.; van der Jeugd, H.; Garigliany, M.; Ziegler, U.; Keller, M.; Lahoreau, J.; Lachmann, J.; Becker, N.; Kik, M.; Oude Munnink, B.B.; Bosch, S.; Tannich, E.; Linden, A.; Schmidt, V.; P Koopmans, M., Rijks, J., Desmecht, D.; H Groschup, M.; Reusken, C.; Schmidt-Chanasit, J. Widespread activity of multiple lineages of Usutu virus, western Europe, 2016. Euro Surveill. 2016, 22, 30452; DOI:10.2807/1560-7917.ES.2017.22.4.30452.
    2. Williams, M.C.; Simpson D.I.; Haddow A.J.; Knight E.M. The isolation of West Nile Virus from man and of Usutu virus from the bird-biting mosquito Mansonia aurites (Theobald) in the Entebbe area of Uganda. Ann. Trop. Med. Parasitol. 1964, 58, 367-374; DOI:10.1080/00034983.1964.11686258.
    3. Nikolay, B.; Diallo, M.; Boye C.S.; Sall A.A. Usutu virus in Africa. Vector Borne Zoonotic Dis. 2011, 11, 1417-1423; DOI:10.1089/vbz.2011.0631.
    4. Durand, B.; Haskouri, H.; Lowenski, S.; Vachiery, N.; Beck, C.; Lecollinet, S. Seroprevalence of West Nile and Usutu viruses in military working horses and dogs, Morocco, 2012: dog as an alternative WNV sentinel species? Epidemiol Infect. 2016, 144(9), 1857-1864; DOI:10.1017/S095026881600011X.
    5. Ben Hassine, T.; De Massis, F.; Calistri, P.; Savini, G.; Bel Haj Mohamed, B.; Ranen, A.; Di Gennaro, A.; Sghaier, S.; Hammami, S. First detection of co-circulation of West Nile and Usutu viruses in equids in the south-west of Tunisia. Transbound Emerg Dis. 2014, 61(5), 385-389; DOI:10.1111/tbed.12259.
    6. Diagne, M.M.; Henriette, M.; Ndione, D.; Di Paola, N.; Fall, G.; Pouwedeou Bedekelabou, A.; Mbacké Sembène, P.; Faye, O.; Marinho de Andrade Zanotto, P.; Sall A.A. Usutu virus isolated from rodents in Senegal. Viruses. 2019, 11(2), 181; DOI:10.3390/v11020181.
    7. Weissenböck, H.; Bakonyi, T.; Rossi, G.; Mani, P.; Nowotny N. Usutu virus, Italy, 1996. Emerg Infect Dis. 2013, 19, 274-277; DOI:10.3201/eid1902.121191.
    8. Weissenböck, H.; Kolodziejek, J.; Url, A.; Lussy, H.; Rebel-Bauder, B.; Nowotny, N. Emergence of Usutu virus, an African mosquito-borne flavivirus of the Japanese encephalitis virus group, central Europe. Emerg Infect Dis. 2002, 8, 652-656; DOI:10.3201/eid0807.020094
    9. Becker, N.; Jöst, H.; Ziegler, U.; Eiden, M.; Höper, D.; Emmerich, P.; Fichet-Calvet, E.; Ehichioya, DU.; Czajka, C.; Gabriel, M.; Hoffmann, B.; Beer, M.; Tenner-Racz, K.; Racz, P.; Günther, S.; Wink, M.; Bosch, S.; Konrad, A.; Pfeffer, M.; Groschup, M.H.; Schmidt-Chanasit, J. Epizootic emergence of Usutu virus in wild and captive birds in Germany. PLoS One. 2012, 7, e32604; DOI: 10.1371/journal.pone.0032604.
    10. Rouffaer, L.O.; Steensels, M.; Verlinden, M.; Vervaeke, M.; Boonyarittichaikij, R.; Martel, A.; Lambrecht, B. Usutu virus epizootic and Plasmodium coinfection in Eurasian blackbirds (Turdus merula) in Flanders, Belgium. J Wildl Dis. 2018, 54, 859-862; DOI:10.7589/2017-07-163.
    11. Zannoli, S.; Sambri V. West Nile virus and Usutu virus co-circulation in Europe: epidemiology and implications. Microorganisms. 2019, 7, e184; DOI:10.3390/microorganisms7070184.
    12. Benzarti, E.; Linden, A.; Desmecht, D.; Garigliany, M. Mosquito-borne epornitic flaviviruses: an updateand review. J Gen Virol. 2019, 100, 119-132, DOI:10.1099/jgv.0.001203.
    13. Jöst, H.; Bialonski, A.; Maus, D.; Sambri, V.; Eiden, M.; Groschup, M.H.; Günther, S.; Becker, N.; Schmidt-Chanasit, J. Isolation of Usutu virus in Germany. Am J Trop Med Hyg. 2011, 85, 551-553; DOI:10.4269/ajtmh.2011.11-0248.
    14. Calzolari, M.; Gaibani, P.; Bellini, R.; Defilippo, F.; Pierro, A.; Albieri, A.; Maioli, G.; Luppi, A.; Rossini, G.; Balzani, A.; Tamba, M.; Galletti, G.; Gelati, A.; Carrieri, M.; Poglayen, G.; Cavrini, F.; Natalini, S.; Dottori, M.; Sambri, V.; Angelini, P.; Bonilauri, P. Mosquito, bird and human surveillance of West Nile and Usutu viruses in Emilia-Romagna Region (Italy) in 2010. PLoS One. 2012, 7, e38058; DOI:10.1371/journal.pone.0038058.
    15. Klobucar, A.; Benic, N.; Krajcar, D.; Kosanovic-Licina, M.L.; Tesic, V.; Merdic, E.; Vrucina, I.; Savic, V.; Barbic, L.; Stevanovic, V.; Pem-Novosel, I.; Vilibic-Cavlek, T. An overview of mosquitoes and emerging arboviral infections in the Zagreb area, Croatia. J Infect Dev Ctries. 2016, 10, 1286-1293; DOI:10.3855/jidc.7988.
    16. Calzolari, M.; Chiapponi, C.; Bonilauri, P.; Lelli, D.; Baioni, L.; Barbieri, I.; Lavazza, A.; Pongolini, S.; Dottori, M.; Moreno, A. Co-circulation of two Usutu virus strains in Northern Italy between 2009 and 2014. Infect Genet Evol. 2017, 51, 255-262; DOI:10.1016/j.meegid.2017.03.022.
    17. Camp, J.V.; Kolodziejek, J.; Nowotny, N. Targeted surveillance reveals native and invasive mosquito species infected with Usutu virus. Parasit Vectors. 2019, 12, 46; DOI:10.1186/s13071-019-3316-z.
    18. Hönig, V.; Palus, M.; Kaspar, T.; Zemanova, M.; Majerova, K.; Hofmannova, L.; Papezik, P.; Sikutova, S.; Rettich, F.; Hubalek, Z.; Rudolf, I.; Votypka, J.; Modry, D.; Ruzek, D. Multiple lineages of Usutu virus (Flaviviridae, Flavivirus) in blackbirds (Turdus merula) and mosquitoes (Culex pipiens, Cx. modestus) in the Czech Republic (2016-2019). Microorganisms. 2019, 7, e568; DOI:10.3390/microorganisms7110568.
    19. Cadar, D.; Becker, N.; Campos Rde, M.; Börstler, J.; Jöst, H.; Schmidt-Chanasit, J. Usutu virus in bats, Germany, 2013. Emerg Infect Dis. 2014, 20, 1771-1773; DOI:10.3201/eid2010.140909.
    20. Benzarti, E.; Sarlet, M.; Franssen, M.; Cadar, D.; Schmidt-Chanasit, J.; Rivas, J.F.; Linden, A.; Desmecht, D.; Garigliany, M. Usutu virus epizootic in Belgium in 2017 and 2018: evidence of virus endemization and ongoing introduction events. Vector Borne Zoonotic Dis. 2020, 20, 43-50; DOI:10.1089/vbz.2019.2469.
    21. Savini, G.; Monaco, F.; Terregino, C.; Di Gennaro, A.; Bano, L.; Pinoni, C.; De Nardi, R.; Bonilauri, P.; Pecorari, M.; Di Gialleonardo, L.; Bonfanti, L.; Polci, A.; Calistri, P.; Lelli, R. Usutu virus in Italy: an emergence or a silent infection? Vet Microbiol. 2011, 151, 264-274; DOI:10.1016/j.vetmic.2011.03.036.
    22. Barbic, L.; Vilibic-Cavlek, T.; Listes, E.; Stevanovic, V.; Gjenero-Margan, I.; Ljubin-Sternak, S.; Pem-Novosel, I.; Listes, I.; Mlinaric-Galinovic, G.; Di Gennaro, A.; Savini, G. Demonstration of Usutu virus antibodies in horses, Croatia. Vector Borne Zoonotic Dis. 2013, 13, 772-774; DOI:10.1089/vbz.2012.1236.
    23. Csank, T.; Drzewnioková, P.; Korytár, Ľ.; Major, P.; Gyuranecz, M.; Pistl, J.; Bakonyi, T. A Serosurvey of flavivirus infection in horses and birds in Slovakia. Vector Borne Zoonotic Dis. 2018, 18, 206-213; DOI:10.1089/vbz.2017.2216.
    24. Montagnaro, S.; Piantedosi, D.; Ciarcia, R.; Loponte, R.; Veneziano, V.; Fusco, G.; Amoroso, M.G.; Ferrara, G.; Damiano, S.; Iovane, G.; Pagnini, U. Serological evidence of mosquito-borne flaviviruses circulation in hunting dogs in Campania Region, Italy. Vector Borne Zoonotic Dis. 2019, 19, 142-147; DOI:10.1089/vbz.2018.2337.
    25. Romeo, C.; Lecollinet, S.; Caballero, J.; Isla, J.; Luzzago, C.; Ferrari, N.; García-Bocanegra, I. Are tree squirrels involved in the circulation of flaviviruses in Italy? Transbound Emerg Dis. 2018, 65, 1372-1376; DOI:10.1111/tbed.12874.
    26. Bournez, L.; Umhang, G.; Faure, E.; Boucher, J.M.; Boué, F.; Jourdain, E.; Sarasa, M.; Llorente, F.; Jiménez-Clavero, M.A.; Moutailler, S.; Lacour, S-A.; Lecollinet, S.; Beck, C. Exposure of wild ungulates to the Usutu and tick-borne encephalitis viruses in France in 2009-2014: evidence of undetected flavivirus circulation a decade ago. Viruses. 2019, 12, e10; DOI:10.3390/v12010010.
    27. Csank, T.; Pikalík, M.; Majláthová, V.; Majláth, I.; Pistl, J. Detection of neutralizing antibodies against Usutu virus in green lizards (Lacerta viridis). Proceedings of the Joint Czechoslovak Virology Conference 2019 and 1st SK-AT Structural Virology Meeting, Bratislava, Slovakia, 13-15 February 2019. Klempa, Nemčovicová, Černý, Tomášková, Stolt-Bergner; Biology Centre AS CR v.v.i; České Budějovice, Czech Republic, 2019. pp. 48-49.
    28. Cavrini, F.; Gaibani, P.; Longo, G.; Pierro, A.M.; Rossini, G.; Bonilauri, P.; Gerunda, G.E.; Di Benedetto, F.; Pasetto, A.; Girardis, M.; Dottori, M.; Landini, M.P.; Sambri, V. Usutu virus infection in a patient who underwent orthotropic liver transplantation, Italy, August-September 2009. Euro Surveill. 2009, 14, 19448.
    29. Pecorari, M.; Longo, G.; Gennari, W.; Grottola, A.; Sabbatini, A.; Tagliazucchi, S.; Savini, G.; Monaco, F.; Simone, M.; Lelli, R.; Rumpianesi, F. First human case of Usutu virus neuroinvasive infection, Italy, August-September 2009. Euro Surveill. 2009, 14, 19446.
    30. Vilibic-Cavlek, T.; Kaic, B.; Barbic, L.; Pem-Novosel, I.; Slavic-Vrzic, V.; Lesnikar, V.; Kurecic-Filipovic, S.; Babic-Erceg, A.; Listes, E.; Stevanovic, V.; Gjenero-Margan, I.; Savini, G. First evidence of simultaneous occurrence of West Nile virus and Usutu virus neuroinvasive disease in humans in Croatia during the 2013 outbreak. Infection. 2014, 42, 689-695. DOI:10.1007/s15010-014-0625-1.
    31. Simonin, Y.; Sillam, O.; Carles, M.J.; Gutierrez, S.; Gil, P.; Constant, O.; Martin, M.F.; Girard, G.; Van de Perre, P.; Salinas, S.; Leparc-Goffart, I.; Foulongne, V. Human Usutu virus infection with atypical neurologic presentation, Montpellier, France, 2016. Emerg Infect Dis. 2018, 24, 875-878: DOI:10.3201/eid2405.171122.
    32. Vilibic-Cavlek, T.; Savic, V.; Sabadi, D.; Peric, L.; Barbic, L.; Klobucar, A.; Miklausic, B.; Tabain, I.; Santini, M.; Vucelja, M.; Dvorski, E.; Butigan, T.; Kolaric-Sviben, G.; Potocnik-Hunjadi, T.; Balenovic, M.; Bogdanic, M.; Andric, Z.; Stevanovic, V.; Capak, K.; Balicevic, M.; Listes, E.; Savini, G. Prevalence and molecular epidemiology of West Nile and Usutu virus infections in Croatia in the 'One health' context, 2018. Transbound Emerg Dis. 2019, 66, 1946-1957; DOI:10.1111/tbed.13225.
    33. Pacenti, M.; Sinigaglia, A.; Martello, T.; De Rui, M.E.; Franchin, E.; Pagni, S.; Peta, E.; Riccetti, S.; Milani, A.; Montarsi, F.; Capelli, G.; Doroldi, C.G.; Bigolin, F.; Santelli, L.; Nardetto, L.; Zoccarato, M.; Barzon, L. Clinical and virological findings in patients with Usutu virus infection, northern Italy, 2018. Euro Surveill. 2019, 24; DOI:10.2807/1560-7917.ES.2019.24.47.1900180.
    34. Bakonyi, T.; Erdélyi, K.; Brunthaler, R.; Dán, Á.; Weissenböck, H.; Nowotny, N. Usutu virus, Austria and Hungary, 2010-2016. Emerg Microbes Infect. 2017, 6, e85; DOI:10.1038/emi.2017.72.
    35. Aberle, S.W.; Kolodziejek, J.; Jungbauer, C.; Stiasny, K.; Aberle, J.H.; Zoufaly, A.; Hourfar, M.K.; Weidner, L.; Nowotny, N. Increase in human West Nile and Usutu virus infections, Austria, 2018. Euro Surveill. 2018, 23; DOI: 10.2807/1560-7917.ES.2018.23.43.1800545.
    36. Garigliany, M.; Linden, A.; Gilliau, G.; Levy, E.; Sarlet, M.; Franssen, M.; Benzarti, E.; Derouaux, A.; Francis, F.; Desmecht, D. Usutu virus, Belgium, 2016. Infect Genet Evol. 2017, 48, 116-119; DOI:10.1016/j.meegid.2016.12.023.
    37. Engel, D.; Jöst, H.; Wink, M.; Börstler J, Bosch S, Garigliany M.M.; Jöst A.; Czajka C.; Lühken, R.; Ziegler, U.; Groschup, M.H.; Pfeffer, M.; Becker, N.; Cadar, D.; Schmidt-Chanasit, J. Reconstruction of the evolutionary history and dispersal of Usutu virus, a neglected emerging arbovirus in Europe and Africa. mBio. 2016, 7, e01938-15; DOI:10.1128/mBio.01938-15.
    38. Weissenböck, H.; Kolodziejek, J.; Fragner. K.; Kuhn, R.; Pfeffer, M.; Nowotny, N. Usutu virus activity in Austria, 2001–2002. Microbes Infect. 2003, 5, 1132-1136; DOI:10.1016/s1286-4579(03)00204-1.
    39. Weidinger, P.; Kolodziejek. J.; Bakonyi, T.; Brunthaler, R.; Erdélyi, K.; Weissenböck, H.; Nowotny, N. Different dynamics of Usutu virus infections in Austria and Hungary, 2017-2018. Transbound Emerg Dis. 2020, 67, 298-307; DOI:10.1111/tbed.13351.
    40. Chvala, S.; Bakonyi, T.; Bukovsky, C.; Meister, T.; Brugger, K.; Rubel, F.; Nowotny, N.; Weissenböck, H. Monitoring of Usutu virus activity and spread by using dead bird surveillance in Austria, 2003-2005. Vet Microbiol. 2007, 122, 237-245; DOI:10.1016/j.vetmic.2007.01.029.
    41. Meister, T.; Lussy, H.; Bakonyi,T.; Sikutová, S.; Rudolf, I.; Vogl, W.; Winkler, H.; Frey, H.; Hubálek, Z.; Nowotny, N.; Weissenböck, H. Serological evidence of continuing high Usutu virus (Flaviviridae) activity and establishment of herd immunity in wild birds in Austria. Vet Microbiol. 2008, 127, 237-248; DOI:10.1016/j.vetmic.2007.08.023.
    42. Buchebner, N.; Zenker, W.; Wenker, C.; Steinmetz, H.W.; Sós, E.; Lussy, H.; Nowotny, N. Low Usutu virus seroprevalence in four zoological gardens in central Europe. BMC Vet. Res. 2013, 9, 153; DOI:10.1186/1746-6148-9-153.
    43. Bakonyi, T.; Jungbauer, C.; Aberle, SW.; Kolodziejek, J.; Dimmel, K.; Stiasny, K.; Allerberger, F.; Nowotny, N. Usutu virus infections among blood donors, Austria, July and August 2017 - Raising awareness for diagnostic challenges. Euro Surveill. 2017, 22; DOI:10.2807/1560-7917.ES.2017.22.41.17-00644.
    44. Garigliany, M.M.; Marlier, D.; Tenner-Racz, K.; Eiden, M.; Cassart, D.; Gandar, F.; Beer, M.; Schmidt-Chanasit, J.; Desmecht, D. Detection of Usutu virus in a bullfinch (Pyrrhula pyrrhula) and a great spotted woodpecker (Dendrocopos major) in north-west Europe. Vet J. 2014, 199, 191-193; DOI:10.1016/j.tvjl.2013.10.017.
    45. Benzarti, E.; Garigliany, M.; Hauman, D.; Paternostre, J.; Linden, A.; Franssen, M.; Sarlet, M.; Cassart, D.; Desmecht, D. First evidence of fatal Usutu virus natural infections in an Anatidae, the Common Scoter (Melanitta nigra). Vector Borne Zoonotic Dis. 2019, 19, 777-780; DOI:10.1089/vbz.2019.2460.
    46. Vilibić-Čavlek, T.; Barbić Lj.; Stevanović, V.; Mlinarić-Galinović, G. Usutu virus: a novel flavivirus in Croatia. Lijec Vjesn. 2015, 137, 46-51. (In Croatian)
    47. Santini, M.; Vilibic-Cavlek, T.; Barsic, B.; Barbic, L.; Savic, V.; Stevanovic, V.; Listes, E.; Di Gennaro, A.; Savini, G. First cases of human Usutu virus neuroinvasive infection in Croatia, August-September 2013: clinical and laboratory features. J Neurovirol. 2015, 21, 92-97; DOI:10.1007/s13365-014-0300-4.
    48. Vilibic-Cavlek, T.; Savic, V.; Petrovic, T.; Toplak, I.; Barbic, L.; Petric, D.; Tabain, I.; Hrnjakovic-Cvjetkovic, I.; Bogdanic, M.; Klobucar, A.; Mrzljak, A.; Stevanovic, V.; Dinjar-Kujundzic, P.; Radmanic, L.; Monaco, F.; Listes, E.; Savini, G. Emerging trends in the epidemiology of West Nile and Usutu virus infections in Southern Europe. Front Vet Sci. 2019, 6, 437; DOI:10.3389/fvets.2019.00437.
    49. Hubálek, Z.; Halouzka, J.; Juricová, Z.; Sikutová, S.; Rudolf, I.; Honza, M.; Janková, J.; Chytil, J.; Marec, F.; Sitko, J. Serologic survey of birds for West Nile flavivirus in southern Moravia (Czech Republic). Vector Borne Zoonotic Dis. 2008, 8, 659-666; DOI:10.1089/vbz.2007.0283.
    50. Hubálek, Z.; Rudolf, I.; Čapek, M.; Bakonyi, T.; Betášová, L.; Nowotny, N. Usutu virus in blackbirds (Turdus merula), Czech Republic, 2011-2012. Transbound Emerg Dis. 2014, 61, 273-276; DOI:10.1111/tbed.12025.
    51. Rudolf, I.; Bakonyi, T.; Šebesta, O.; Mendel, J.; Peško, J.; Betášová, L.; Blažejová, H.; Venclíková, K.; Straková, P.; Nowotny, N.; Hubálek, Z. Co-circulation of Usutu virus and West Nile virus in a reed bed ecosystem. Parasit Vectors. 2015, 8, 520; DOI:10.1186/s13071-015-1139-0.
    52. Vittecoq, M.; Lecollinet, S.; Jourdain, E.; Thomas, F.; Blanchon, T.; Arnal, A.; Lowenski, S.; Gauthier-Clerc, M. Recent circulation of West Nile virus and potentially other closely related flaviviruses in Southern France. Vector Borne Zoonotic Dis. 2013, 13, 610-613; DOI:10.1089/vbz.2012.1166.
    53. Lecollinet, S.; Blanchard, Y.; Manson, C.; Lowenski, S.; Laloy, E.; Quenault, H.; Touzain, F.; Lucas, P.; Eraud, C.; Bahuon, C.; Zientara, S.; Beck, C.; Decors, A. Dual emergence of Usutu virus in common blackbirds, Eastern France, 2015. Emerg Infect Dis. 2016, 22, 2225; DOI:10.3201/eid2212.161272.
    54. Eiden, M.; Gil, P.; Ziegler, U.; Rakotoarivony, I.; Marie, A.; Frances, B.; L'Ambert, G.; Simonin, Y.; Foulongne, V.; Groschup, M.H.; Gutierrez, S.; Eloit, M. Emergence of two Usutu virus lineages in Culex pipiens mosquitoes in the Camargue, France, 2015. Infect Genet Evol. 2018, 61, 151-154; DOI:10.1016/j.meegid.2018.03.020.
    55. Roesch, F.; Fajardo, A.; Moratorio, G.; Vignuzzi, M. Usutu virus: An arbovirus on the rise. Viruses. 2019, 11, 640; DOI:10.3390/v11070640.
    56. Ziegler, U.; Jöst, H.; Müller, K.; Fischer, D.; Rinder, M.; Tietze, D.T.; Danner, K.J.; Becker, N.; Skuballa, J.; Hamann, H.P.; Bosch, S.; Fast, C.; Eiden, M.; Schmidt-Chanasit, J.; Groschup, M.H. Epidemic spread of Usutu virus in Southwest Germany in 2011 to 2013 and monitoring of wild birds for Usutu and West Nile viruses. Vector Borne Zoonotic Dis. 2015, 15, 481-488; DOI:10.1089/vbz.2014.1746.
    57. Allering, L; Jöst, H; Emmerich, P; Günther, S; Lattwein, E; Schmidt, M; Seifried, E; Sambri, V; Hourfar, K; Schmidt-Chanasit, J. Detection of Usutu virus infection in a healthy blood donor from south-west Germany, 2012. Euro Surveill. 2012; 17(50). pii: 20341.
    58. Lühken, R.; Jöst, H.; Cadar, D.; Thomas, S.M.; Bosch, S.; Tannich, E.; Becker, N.; Ziegler, U.; Lachmann, L.; Schmidt-Chanasit, J. Distribution of Usutu virus in Germany and its effect on breeding bird populations. Emerg Infect Dis. 2017, 23, 1994-2001; DOI:10.3201/eid2312.171257.
    59. Scheuch, D.E.; Schäferm M.; Eiden, M.; Heym, E.C.; Ziegler, U.; Walther, D.; Schmidt-Chanasit, J.; Keller, M.; Groschup, M.H.; Kampen, H. Detection of Usutu, Sindbis, and Batai viruses in mosquitoes (Diptera: Culicidae) collected in Germany, 2011⁻2016. Viruses. 2018, 10, E389; DOI:10.3390/v10070389.
    60. Ziegler, U.; Fast, C.; Eiden, M.; Bock, S.; Schulze, C.; Hoeper, D.; Ochs, A.; Schlieben, P.; Keller, M.; Zielke, D.E.; Luehken, R.; Cadar, D.; Walther, D.; Schmidt-Chanasit, J.; Groschup, M,H. Evidence for an independent third Usutu virus introduction into Germany. Vet Microbiol. 2016, 192, 60-66; DOI:10.1016/j.vetmic.2016.06.007.
    61. Sieg, M.; Schmidt, V.; Ziegler, U.; Keller, M.; Höper, D., Heenemann, K.; Rückner, A.; Nieper, H.; Muluneh, A.; Groschup, M.H.; Vahlenkamp, T.W. Outbreak and cocirculation of three different Usutu virus strains in Eastern Germany. Vector Borne Zoonotic Dis. 2017, 17, 662-664; DOI:10.1089/vbz.2016.2096.
    62. Llopis, I.V.; Rossi, L.; Di Gennaro, A.; Mosca, A.; Teodori, L.; Tomassone, L.; Grego, E.; Monaco, F.; Lorusso, A.; Savini, G. Further circulation of West Nile and Usutu viruses in wild birds in Italy. Infect. Genet. Evol. 2015, 32, 292–297.
    63. Pautasso, A.; Radaelli, M.C.; Ballardini, M.; Francese, D.R.; Verna, F.; Modesto, P.; Grattarola, C.; Desiato, R.; Bertolini, S.; Vitale, N.; et al. Detection of West Nile and Usutu Viruses in Italian Free Areas: Entomological Surveillance in Piemonte and Liguria Regions, 2014. Vector Borne Zoonotic Dis. 2016, 16, 292–294.
    64. Daniel Cadar; Philipp Maier; Susanne Müller; Julia Kress; Michael Chudy; Alexandra Bialonski; Alexander Schlaphof; Stephanie Jansen; Hanna Jöst; Egbert Tannich; et al. Blood donor screening for West Nile virus (WNV) revealed acute Usutu virus (USUV) infection, Germany, September 2016. Eurosurveillance 2017, 22, 30501, 10.2807/1560-7917.es.2017.22.14.30501.
    65. Ute Ziegler; Hanna Jöst; Kerstin Müller; D. Fischer; Monika Rinder; Dieter Thomas Tietze; Klaus-Jürgen Danner; Norbert Becker; Jasmin Skuballa; Hans-Peter Hamann; et al. Epidemic Spread of Usutu Virus in Southwest Germany in 2011 to 2013 and Monitoring of Wild Birds for Usutu and West Nile Viruses. Vector-Borne and Zoonotic Diseases 2015, 15, 481-488, 10.1089/vbz.2014.1746.
    66. Pia Weidinger; Jolanta Kolodziejek; Tamás Bakonyi; René Brunthaler; Károly Erdélyi; Herbert Weissenböck; Norbert Nowotny; Different dynamics of Usutu virus infections in Austria and Hungary, 2017–2018. Transboundary and Emerging Diseases 2019, 67, 298-307, 10.1111/tbed.13351.
    67. Hubálek, Z.; Rudolf, I.; Čapek, M.; Bakonyi, T.; Betášová, L.; Nowotny, N. Usutu virus in blackbirds (Turdus merula), Czech Republic, 2011–2012. Transbound. Emerg. Dis. 2014, 61, 273–276.
    68. Sieg, M.; Schmidt, V.; Ziegler, U.; Keller, M.; Höper, D.; Heenemann, K.; Rückner, A.; Nieper, H.; Muluneh, A.; Groschup, M.H.; et al. Outbreak and Cocirculation of Three Different Usutu Virus Strains in Eastern Germany. Vector Borne Zoonotic Dis. 2017, 17, 662–664.
    69. Michel, F.; Sieg, M.; Fischer, D.; Keller, M.; Eiden, M.; Reuschel, M.; Schmidt, V.; Schwehn, R.; Rinder, M.; Urbaniak, S.; et al. Evidence for West Nile Virus and Usutu Virus Infections in Wild and Resident Birds in Germany, 2017 and 2018. Viruses 2019, 11, 674.
    70. Tamás Bakonyi; Károly Erdélyi; Krisztina Ursu; Emoke Ferenczi; Tibor Csörgo; Helga Lussy; Sonja Chvala; Christiane Bukovsky; Tanja Meister; Herbert Weissenböck; et al. Emergence of Usutu Virus in Hungary. Journal of Clinical Microbiology 2007, 45, 3870-3874, 10.1128/jcm.01390-07.
    71. Caracciolo, I.; Cardenas, E.M.; Aloise, C.; Carletti, T.; Segat, L.; Burali, M.S.; Chiarvesio, A.; Totis, V.; Avšič–Županc, T.; Mastrangelo, E.; et al. Comprehensive response to Usutu virus following first isolation in blood donors in the Friuli Venezia Giulia region of Italy: Development of recombinant NS1-based serology and sensitivity to antiviral drugs. PLoS Negl. Trop. Dis. 2020, 14, e0008156.
    72. Carletti, F.; Colavita, F.; Rovida, F.; Percivalle, E.; Baldanti, F.; Ricci, I.; De Liberato, C.; Rosone, F.; Messina, F.; Lalle, E.; et al. Expanding Usutu virus circulation in Italy: Detection in the Lazio region, central Italy, 2017 to 2018. Eurosurveillance 2019, 24, 1800649.
    73. Munnink, B.B.O.; Münger, E.; Nieuwenhuijse, D.F.; Kohl, R.; Van Der Linden, A.; Schapendonk, C.M.E.; Van Der Jeugd, H.; Kik, M.; Rijks, J.M.; Reusken, C.B.E.M.; et al. Genomic monitoring to understand the emergence and spread of Usutu virus in the Netherlands, 2016–2018. Sci. Rep. 2020, 10, 1–10.
    74. Zaaijer, H.L.; Slot, E.; Molier, M.; Reusken, C.B.; Koppelman, M.H. Usutu virus infection in Dutch blood donors. Transfusion 2019, 59, 2931–2937.
    75. Kemenesi, G.; Buzás, D.; Zana, B.; Kurucz, K.; Krtinić, B.; Kepner, A.; Földes, F.; Jakab, F. First genetic characterization of Usutu virus from Culex pipiens mosquitoes Serbia, 2014. Infect. Genet. Evol. 2018, 63, 58–61.
    76. Petrović, T.; Šekler, M.; Petrić, D.; Vidanović, D.; Potkonjak, A.; Cvjetković, I.H.; Savić, S.; Debeljak, Z.; Lazić, G.; Ćupina, A.I.; et al. Flaviviruses at the territory of Serbia—Present situation and challenges. Arch. Vet. Med. 2018, 11, 53–70.
    77. Ana Vázquez; Juana Moreno; Antonio Tenorio; Jordi Figuerola; Maria Paz Sánchez-Seco; Santiago Ruiz; Antonio Magallanes; Francisca Molero; Laura Herrero; West Nile and Usutu Viruses in Mosquitoes in Spain, 2008–2009. The American Journal of Tropical Medicine and Hygiene 2011, 85, 178-181, 10.4269/ajtmh.2011.11-0042.
    78. Rizzo, C.; Napoli, C.; Venturi, G.; Pupella, S.; Lombardini, L.; Calistri, P.; Monaco, F.; Cagarelli, R.; Angelini, P.; Bellini, R.; et al. West Nile virus transmission: Results from the integrated surveillance system in Italy, 2008 to 2015. Eurosurveillance 2016, 21.
    79. Young, J.J.; Coulombier, D.; Domanović, D.; Zeller, H.; Gossner, C.M.; European Union West Nile Fever Working Group. One Health approach for West Nile virus surveillance in the European Union: Relevance of equine data for blood safety. Eurosurveillance 2019, 24, 1800349.
    80. Vilibic-Cavlek, T.; Vidanović, D.; Barbić, L.; Jeličić, P.; Lazić, S.; Radmanić, L.; Lupulović, D.; Janev-Holcer, N.; Tešović, B.; Milošević, V.; et al. Importance of Multidisciplinary and Regional Collaboration in Integrated West Nile Virus Surveillance—The “One Health” Concept. Infektološki Glasn. 2019, 39, 40–47.