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Home / Equine Research Bank / Vet Res / Introduction of West Nile virus lineage 2 leads to neuroinva...
Veterinary research2025; 56(1); 177; doi: 10.1186/s13567-025-01575-z

Introduction of West Nile virus lineage 2 leads to neuroinvasive cases in humans and horses in Sicily, 2022-2023.

Abstract: In Italy, West Nile virus (WNV) has been consistently causing disease in humans, horses, and birds since 2008; it was initially confined to the northeast of the country and then spread gradually to the western and southern regions. WNV lineage 1 (WNV-L1) virus was the only lineage that circulated in Italy until 2011, but it was progressively replaced by WNV lineage 2 (WNV-L2). WNV disease in humans was not observed in Sicily, southern Italy, until 2016, when the first case of West Nile neuroinvasive disease (WNND) due to WNV-L1 was reported. Our results demonstrate the introduction of WNV-L2 in Sicily via the detection of four equine and five human cases of WNND reported in western Sicily in September 2022. Local WNV circulation was confirmed by virological and serological investigations in horses, birds, and dogs. WNV-L2 was demonstrated to be the strain responsible for both human and equine neuroinvasive cases and continued to circulate in western Sicily in 2023, where it was detected in insects and in a neuroinvasive human case in August.
© 2025. The Author(s).
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Publication Date: 2025-09-25 PubMed ID: 40999548PubMed Central: PMC12465315DOI: 10.1186/s13567-025-01575-zGoogle Scholar: Lookup
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Summary

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Overview

  • This research article reports on the introduction and spread of West Nile virus lineage 2 (WNV-L2) in Sicily, Italy, during 2022-2023, causing neuroinvasive disease cases in both humans and horses.
  • It highlights the transition from the previously dominant lineage 1 (WNV-L1) to lineage 2, demonstrating local circulation and ongoing outbreaks in the region.

Background on West Nile Virus in Italy

  • West Nile virus (WNV) is a mosquito-borne virus that affects humans, horses, and birds, occasionally leading to severe neuroinvasive disease.
  • In Italy, WNV has been known to cause disease since 2008, initially limited to the northeast part of the country.
  • There was a gradual geographical expansion of the virus towards western and southern regions over time.
  • Until 2011, only WNV lineage 1 (WNV-L1) circulated in Italy, after which WNV lineage 2 (WNV-L2) progressively replaced it.
  • Notably, West Nile neuroinvasive disease (WNND) had not been observed in humans in Sicily until 2016, when the first human case associated with WNV-L1 was reported.

Findings in Sicily, 2022-2023

  • In 2022, the study detected the introduction of WNV-L2 in western Sicily.
  • Four horses and five humans were reported with neuroinvasive disease caused by WNV-L2 in September 2022.
  • Local viral circulation was confirmed through:
    • Virological investigations (detecting the virus in biological samples)
    • Serological investigations (detecting antibodies indicating past infection)
    • Testing conducted on horses, birds, and dogs in the area
  • The research demonstrated that WNV-L2 is responsible for causing neuroinvasive disease cases in both humans and horses in western Sicily.
  • WNV-L2 circulation continued into 2023, with detections in insects (the mosquito vectors) and a new human neuroinvasive case reported in August 2023.

Significance of the Study

  • This study documents an important shift in the epidemiology of West Nile virus in Sicily, with the emergence and establishment of WNV-L2.
  • The findings suggest that WNV-L2 is now actively circulating among vectors and susceptible hosts in western Sicily, posing ongoing risks to public and animal health.
  • Demonstrating both human and equine cases confirms zoonotic transmission and highlights the need for continued surveillance and preventive measures.
  • The study provides data essential for guiding health authorities in mosquito control, disease prevention, and clinical management strategies in Sicily and similar regions.

Cite This Article

APA
(2025). Introduction of West Nile virus lineage 2 leads to neuroinvasive cases in humans and horses in Sicily, 2022-2023. Vet Res, 56(1), 177. https://doi.org/10.1186/s13567-025-01575-z

Publication

Veterinary research
ISSN: 1297-9716
NlmUniqueID: 9309551
Country: England
Language: English
Volume: 56
Issue: 1
Pages: 177
PII: 177

Researcher Affiliations

MeSH Terms

  • Animals
  • West Nile virus / genetics
  • West Nile virus / isolation & purification
  • West Nile virus / physiology
  • West Nile virus / classification
  • Horses
  • West Nile Fever / veterinary
  • West Nile Fever / virology
  • West Nile Fever / epidemiology
  • Sicily / epidemiology
  • Horse Diseases / virology
  • Horse Diseases / epidemiology
  • Humans
  • Male
  • Dogs
  • Female
  • Dog Diseases / virology
  • Dog Diseases / epidemiology
  • Birds

Grant Funding

  • IZS SI 05/23 RC / Ministero della Salute
  • IZS SI 06/21 RC / Ministero della Salute

Conflict of Interest Statement

Declarations. Ethics approval and consent to participate: The collection of data used for this manuscript is compulsory in Italy in accordance with the Italian West Nile Virus PNA guidelines as part of routine clinical surveillance activities. This system is designed to document and register the occurrence and progression of significant infectious animal diseases in accordance with Council Directive 82/894/EC. The consensus for the collection of these data is not mandatory and is based on Guideline 12 of the WHO on ethical issues in public health surveillance. Competing interests: The authors declare that they have no competing interests.

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