2025-07-09
West Nile: the fever is rising!
Infectiology
#WestNile #Mosquito #Epidemiology #Zoonosis
West Nile Virus (WNV), an arbovirus transmitted by mosquitoes and primarily hosted by birds, represents a major public health concern in the Mediterranean region. This zoonotic disease can cause clinical manifestations ranging from mild symptoms to severe encephalitis, especially in the elderly or immunocompromised individuals.
Despite the existence of surveillance systems in many Mediterranean countries, control measures remain limited due to the lack of a human vaccine and curative treatment. Prevention relies mainly on vector control and early detection of outbreaks. One of the main challenges lies in the silent circulation of the virus in endemic areas, facilitated by climate change, avian migratory flows, and the diversity of mosquito vectors. Additionally, disparities in surveillance strategies between countries make epidemic forecasting difficult.
This study aims to provide an updated overview of WNV epidemiology in the Mediterranean Basin from 2010 to 2023 by analyzing spatiotemporal trends, host species, circulating viral lineages, and the effectiveness of surveillance systems.
The study is based on the analysis of data collected from 20 Mediterranean countries between 2010 and 2023. It draws on national epidemiological reports, notifications to the ECDC and OIE, and scientific publications. Human and animal cases (mainly equine), as well as environmental detections (mosquitoes, birds), were included, with special focus on viral lineages (WNV-1 and WNV-2) identified through sequencing.
The study reveals a general increase in human and animal cases during the study period, with a major peak in 2018. The most affected countries include Italy, Greece, Serbia, Tunisia, and Turkey. The virus circulates primarily between June and October, with a progressive geographic expansion toward the north.
Two viral lineages predominate: WNV-1, historically the most common, and WNV-2, responsible for an epidemic resurgence since 2010. Transmission is strongly influenced by climatic conditions, especially high summer temperatures and spring rainfall. The data also show an increase in early detections in mosquitoes and birds, reflecting improved integrated surveillance systems (a "One Health" approach).
West Nile virus remains a priority pathogen in the Mediterranean Basin due to its endemic presence, epidemic potential, and the absence of specific treatment. Surveillance is especially critical for anticipating seasonal outbreaks. Key challenges include the heterogeneity of surveillance systems, lack of standardized data across countries, and the difficulty of predicting epidemics based on ecological conditions. This study aimed to consolidate regional epidemiological knowledge to better target interventions.
The results highlight the need for an integrated approach that combines human, animal, and entomological surveillance to enable early detection and effective epidemic risk management. However, the analysis remains hampered by disparities in surveillance systems, lack of common indicators, and incomplete data availability.
To strengthen the fight against West Nile virus, several strategies should be considered: harmonizing epidemiological monitoring strategies at the regional level, integrating climate modeling into forecasting tools, accelerating the development of human vaccines, and establishing coordinated prevention programs between countries. WNV thus emerges as a sensitive indicator of increasing tensions between human health, environmental factors, and climate dynamics.
West Nile Virus (WNV), an arbovirus transmitted by mosquitoes and primarily hosted by birds, represents a major public health concern in the Mediterranean region. This zoonotic disease can cause clinical manifestations ranging from mild symptoms to severe encephalitis, especially in the elderly or immunocompromised individuals.
Despite the existence of surveillance systems in many Mediterranean countries, control measures remain limited due to the lack of a human vaccine and curative treatment. Prevention relies mainly on vector control and early detection of outbreaks. One of the main challenges lies in the silent circulation of the virus in endemic areas, facilitated by climate change, avian migratory flows, and the diversity of mosquito vectors. Additionally, disparities in surveillance strategies between countries make epidemic forecasting difficult.
This study aims to provide an updated overview of WNV epidemiology in the Mediterranean Basin from 2010 to 2023 by analyzing spatiotemporal trends, host species, circulating viral lineages, and the effectiveness of surveillance systems.
Read next: Chikungunya: the invisible epidemic
West nile: where, when, and why is it surging?
The study is based on the analysis of data collected from 20 Mediterranean countries between 2010 and 2023. It draws on national epidemiological reports, notifications to the ECDC and OIE, and scientific publications. Human and animal cases (mainly equine), as well as environmental detections (mosquitoes, birds), were included, with special focus on viral lineages (WNV-1 and WNV-2) identified through sequencing.
The study reveals a general increase in human and animal cases during the study period, with a major peak in 2018. The most affected countries include Italy, Greece, Serbia, Tunisia, and Turkey. The virus circulates primarily between June and October, with a progressive geographic expansion toward the north.
Two viral lineages predominate: WNV-1, historically the most common, and WNV-2, responsible for an epidemic resurgence since 2010. Transmission is strongly influenced by climatic conditions, especially high summer temperatures and spring rainfall. The data also show an increase in early detections in mosquitoes and birds, reflecting improved integrated surveillance systems (a "One Health" approach).
Read next: Virus & fertility: when does the barrier break down?
A well-established virus, a future to monitor
West Nile virus remains a priority pathogen in the Mediterranean Basin due to its endemic presence, epidemic potential, and the absence of specific treatment. Surveillance is especially critical for anticipating seasonal outbreaks. Key challenges include the heterogeneity of surveillance systems, lack of standardized data across countries, and the difficulty of predicting epidemics based on ecological conditions. This study aimed to consolidate regional epidemiological knowledge to better target interventions.
The results highlight the need for an integrated approach that combines human, animal, and entomological surveillance to enable early detection and effective epidemic risk management. However, the analysis remains hampered by disparities in surveillance systems, lack of common indicators, and incomplete data availability.
To strengthen the fight against West Nile virus, several strategies should be considered: harmonizing epidemiological monitoring strategies at the regional level, integrating climate modeling into forecasting tools, accelerating the development of human vaccines, and establishing coordinated prevention programs between countries. WNV thus emerges as a sensitive indicator of increasing tensions between human health, environmental factors, and climate dynamics.
Read next: Dengue and the Mind: The Silent Storm
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