One Health surveillance of West Nile and Usutu viruses: a repeated cross-sectional study exploring seroprevalence and endemicity in Southern France, 2016 to 2020

Abstract

Background West Nile virus (WNV) and Usutu virus (USUV), two closely related flaviviruses, mainly follow an enzootic cycle involving mosquitoes and birds, but also infect humans and other mammals. Since 2010, their epidemiological situation may have shifted from irregular epidemics to endemicity in several European regions; this requires confirmation, as it could have implications for risk assessment and surveillance strategies. Aim To explore the seroprevalence in animals and humans and potential endemicity of WNV and USUV in Southern France, given a long history of WNV outbreaks and the only severe human USUV case in France in this region. Methods We evaluated the prevalence of WNV and USUV in a repeated cross-sectional study by serological and molecular analyses of human, dog, horse, bird and mosquito samples in the Camargue area, including the city of Montpellier, between 2016 and 2020. Results We observed the active transmission of both viruses and higher USUV prevalence in humans, dogs, birds and mosquitoes, while WNV prevalence was higher in horses. In 500 human samples, 15 were positive for USUV and 6 for WNV. Genetic data showed that the same lineages, WNV lineage 1a and USUV lineage Africa 3, were found in mosquitoes in 2015, 2018 and 2020. Conclusion These findings support existing literature suggesting endemisation in the study region and contribute to a better understanding of USUV and WNV circulation in Southern France. Our study underlines the importance of a One Health approach for the surveillance of these viruses.

Screening of Circulation of Usutu and West Nile Viruses: A One Health Approach in Humans, Domestic Animals and Mosquitoes in Burkina Faso, West Africa

“…To validate the negative results of our RT-qPCR, we always added a positive sample (RNA isolated from cell culture infections) in our PCR plates. Moreover, we have analyzed in parallel and with the same RT-qPCR a batch of mosquitoes from France [ 25 ]. Our results with the French samples show that our RT-qPCR is able to detect both viruses and allows to identify positive samples for virus isolation and genome sequencing.…”

Differential effects of Usutu and West Nile viruses on neuroinflammation, immune cell recruitment and blood–brain barrier integrity

“…Indeed, they share a similar enzootic cycle involving birds as reservoirs and mainly Culex mosquitoes as vectors [ 18 ]. The risk of human epidemic is also increasing and lot of efforts are being made to investigate virus distribution and molecular characteristics [ 19 , 20 ]. Neurological disorders associated to human USUV and WNV infections are caused by efficient viral neurotropism.…”

Early start of seasonal transmission and co-circulation of West Nile virus lineage 2 and a newly introduced lineage 1 strain, northern Italy, June 2022

“…A small sequence (182 nt) of the nonstructural protein 5 gene was obtained from the WNV-1 strains detected in humans in 2021 and 2022, which were identical to the sequences detected in mosquitoes and birds ( Figure 3 ). Among published WNV sequences, the highest similarity (98.5% nucleotide sequence identity) was demonstrated with two viruses identified in southern France in 2015 and 2018 [ 6 ].…”