Widespread circulation of West Nile and Usutu viruses in sedentary and migratory avifauna: A two-year study (2024–2025) of active surveillance in South of France
Abstract
West Nile virus (WNV) and Usutu virus (USUV) are neurotropic Orthoflaviviruses sharing a similar enzootic transmission cycle primarily involving Culex pipiens mosquitoes as vectors and birds as amplifying hosts. First identified in Africa, both viruses established endemicity across Europe over the past two decades, most likely introduced and spread by migratory bird species along Mediterranean flyways. In avian species, infection outcomes range from subclinical to fatal neuroinvasive disease, varying by viral strain, host immunity, and species sensibility. Southern France emerges as a key hotspot for the circulation of these viruses, supported by diverse avian habitats conducive to year-round viral maintenance. This study investigated the RNA prevalence of WNV and USUV in more than 2500 sedentary and migratory wild birds from this region during 2024–2025 using molecular surveillance. Samples were collected using mists net and bird boxes, across multiple passerine and non-passerine taxa, spanning wetlands, urban fringes, and agricultural zones. Our analyses revealed widespread viral detection across diverse species, mainly among passerines such as great tits, house sparrows, and barn swallows with USUV detected at higher rates than WNV in both study years. Overall RNA prevalence was markedly higher in 2024 than in 2025, potentially reflecting climatic or ecological drivers. These results highlight the pivotal role of mixed avifauna in arbovirus dynamics within Mediterranean Europe and emphasize the necessity for integrated, year-round surveillance targeting high-risk species and habitats. Author summary: West Nile virus and Usutu virus are two closely related viruses spread by mosquitoes that mainly infect birds but can occasionally cause severe neurological disease in humans and horses. Southern France, and in particular the Camargue wetlands near Montpellier, is a long-recognised hotspot for both viruses. Over two years (2024–2025), we sampled more than 2,500 wild birds of 69 species in this region, testing cloacal swabs and droppings for viral RNA. Both viruses circulated widely, with Usutu virus detected roughly three times more often than West Nile virus, and overall circulation was higher in 2024 than in 2025 and more frequent in rural, wetland-associated sites. Our findings reinforce the value of active, non-invasive avian surveillance as a complement to existing human and veterinary case reporting for these viruses in Europe.
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BibTeX
@article{beaubaton2026widespread,
title = {{Widespread circulation of West Nile and Usutu viruses in sedentary and migratory avifauna: A two-year study (2024–2025) of active surveillance in South of France}},
author = {Rachel Beaubaton and Justine Revel and Laetitia Pigeyre and Alexandre Lepeule and Julien Joly and Christophe de Franceschi and Anne Charmantier and Benjamin Vollot and Yannick Simonin},
journal = {PLoS Neglected Tropical Diseases},
year = {2026},
month = sep,
doi = {10.1371/journal.pntd.0014397},
url = {https://hal.science/hal-05756786v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Widespread circulation of West Nile and Usutu viruses in sedentary and migratory avifauna: A two-year study (2024–2025) of active surveillance in South of France
AU - Rachel Beaubaton
AU - Justine Revel
AU - Laetitia Pigeyre
AU - Alexandre Lepeule
AU - Julien Joly
AU - Christophe de Franceschi
AU - Anne Charmantier
AU - Benjamin Vollot
AU - Yannick Simonin
PY - 2026
DA - 2026/09/03
JO - PLoS Neglected Tropical Diseases
DO - 10.1371/journal.pntd.0014397
UR - https://hal.science/hal-05756786v1
AB - West Nile virus (WNV) and Usutu virus (USUV) are neurotropic Orthoflaviviruses sharing a similar enzootic transmission cycle primarily involving Culex pipiens mosquitoes as vectors and birds as amplifying hosts. First identified in Africa, both viruses established endemicity across Europe over the past two decades, most likely introduced and spread by migratory bird species along Mediterranean flyways. In avian species, infection outcomes range from subclinical to fatal neuroinvasive disease, varying by viral strain, host immunity, and species sensibility. Southern France emerges as a key hotspot for the circulation of these viruses, supported by diverse avian habitats conducive to year-round viral maintenance. This study investigated the RNA prevalence of WNV and USUV in more than 2500 sedentary and migratory wild birds from this region during 2024–2025 using molecular surveillance. Samples were collected using mists net and bird boxes, across multiple passerine and non-passerine taxa, spanning wetlands, urban fringes, and agricultural zones. Our analyses revealed widespread viral detection across diverse species, mainly among passerines such as great tits, house sparrows, and barn swallows with USUV detected at higher rates than WNV in both study years. Overall RNA prevalence was markedly higher in 2024 than in 2025, potentially reflecting climatic or ecological drivers. These results highlight the pivotal role of mixed avifauna in arbovirus dynamics within Mediterranean Europe and emphasize the necessity for integrated, year-round surveillance targeting high-risk species and habitats. Author summary: West Nile virus and Usutu virus are two closely related viruses spread by mosquitoes that mainly infect birds but can occasionally cause severe neurological disease in humans and horses. Southern France, and in particular the Camargue wetlands near Montpellier, is a long-recognised hotspot for both viruses. Over two years (2024–2025), we sampled more than 2,500 wild birds of 69 species in this region, testing cloacal swabs and droppings for viral RNA. Both viruses circulated widely, with Usutu virus detected roughly three times more often than West Nile virus, and overall circulation was higher in 2024 than in 2025 and more frequent in rural, wetland-associated sites. Our findings reinforce the value of active, non-invasive avian surveillance as a complement to existing human and veterinary case reporting for these viruses in Europe.
SN - 1935-2727
SN - 1935-2735
ER -