Emerging Trends in the Epidemiology of West Nile and Usutu Virus Infections in Southern Europe.
Authors: Vilibic-Cavlek Tatjana, Savic Vladimir, Petrovic Tamas, Toplak Ivan, Barbic Ljubo, Petric Dusan, Tabain Irena, Hrnjakovic-Cvjetkovic Ivana, Bogdanic Maja, Klobucar Ana, Mrzljak Anna, Stevanovic Vladimir, Dinjar-Kujundzic Petra, Radmanic Luka, Monaco Federica, Listes Eddy, Savini Giovanni
Journal: Frontiers in veterinary science
Summary
# Editorial Summary: West Nile and Usutu Virus Epidemiology in Southern Europe West Nile virus (WNV) and Usutu virus (USUV) represent an evolving public health and animal welfare concern across Southern Europe, with both pathogens expanding their geographical range and vector populations over the past two decades. This comprehensive review examined epidemiological data from multiple countries, tracking viral circulation patterns in humans, horses, birds and mosquito vectors, and identified that whilst WNV has been established since 1999, USUV only emerged in equine populations as recently as 2009, yet seroepidemiological evidence suggests it may now circulate more widely than WNV in some endemic regions. The primary vector remains *Culex pipiens*, but experimental and field evidence now confirms transmission competence across multiple native and invasive mosquito species including *Aedes albopictus* and *Aedes japonicus*, substantially widening the potential for viral dispersal. Lineage 2 WNV strains currently predominate in European human and equine cases, whilst both European and African USUV lineages have been documented, indicating possible evolving viral origins. For equine practitioners, this expanding epidemiological landscape necessitates heightened vigilance for neuroinvasive disease presentation, particularly in endemic regions, alongside awareness that vector populations may extend beyond traditional high-risk periods and habitats, informing biosecurity and client education strategies around mosquito control.
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Practical Takeaways
- •Equine practitioners in Southern Europe should be alert to WNV and USUV as differential diagnoses in horses presenting with neurological signs, particularly given confirmed seroconversion in the equine population
- •Mosquito vector control efforts should target both Culex pipiens (primary vector) and invasive Aedes species, as multiple vector species are now competent for viral transmission
- •Consider USUV in disease investigations despite its sporadic detection in humans; seroepidemiological data suggests it may be under-recognised due to lower neuroinvasive rates compared to WNV
Key Findings
- •West Nile virus has expanded circulation across Southern Europe since 1999 with predominantly lineage 2 strains detected in humans, horses, birds and mosquitoes
- •Usutu virus seroconversion was first reported in horses in Italy in 2009, with seroepidemiological evidence showing USUV circulation exceeds WNV in some endemic regions
- •Culex pipiens remains the primary vector, but experimental transmission competence confirmed in native species (Cx. modestus, Cx. perexiguus) and invasive Aedes species (Ae. albopictus, Ae. detritus, Ae. japonicus)
- •Co-circulation of both WNV and USUV detected across humans, horses and birds with increasing evidence of USUV involvement in human neuroinvasive disease