Reoccurrence of West Nile virus lineage 1 after 2-year decline: first equine outbreak in Campania region.
Authors: de Martinis Claudio, Cardillo Lorena, Pesce Federica, Viscardi Maurizio, Cozzolino Loredana, Paradiso Rubina, Cavallo Stefania, De Ascentis Matteo, Goffredo Maria, Monaco Federica, Savini Giovanni, D'Orilia Francescantonio, Pinto Renato, Fusco Giovanna
Journal: Frontiers in veterinary science
Summary
# Editorial Summary West Nile virus lineage 1 (WNV-L1) had been absent from Italy for approximately a decade before resurfacing in 2020, and this 2023 investigation documents its first confirmed equine case in the Campania region—a fatal neurological infection in a 7-year-old horse with viral detection across multiple organs (heart, brain, gut, liver, spleen) via real-time RT-PCR. Phylogenetic and next-generation sequencing analysis revealed >98% nucleotide identity between the equine isolate and a strain recovered from a goshawk (*Accipiter gentilis*) in the same locality two years prior, both belonging to the WNV-L1 Western-Mediterranean sub-cluster, suggesting cryptic viral circulation during an extended 2-year period when conventional serological and biomolecular surveillance detected nothing in equine, avian, or mosquito populations. The findings highlight a critical epidemiological phenomenon: WNV-L1 likely persisted in wildlife reservoirs at levels below detection thresholds before manifesting as clinical disease, with climatic shifts creating conditions favouring viral re-establishment in historically low-risk zones. For equine professionals, this underscores the importance of maintaining vigilance for neurological signs consistent with WNV even during apparent absence of active transmission, implementing robust vector control during appropriate seasons, and recognising that surveillance silence does not guarantee freedom from circulation—particularly as global warming continues reshaping arbovirus epidemiology.
Read the full abstract on PubMed
Practical Takeaways
- •Clinicians in Mediterranean regions should maintain awareness of WNV-L1 as a differential diagnosis for acute neurological disease in horses, even in areas with apparent absence of disease for years
- •Expect the possibility of silent viral circulation between obvious clinical cases; surveillance programs should continue even during apparent eclipse periods to detect re-emergence early
- •Climate change may expand geographic range and alter seasonal patterns of WNV; biosecurity measures against insect vectors remain important despite variable disease activity
Key Findings
- •WNV-L1 reappeared in Italy after a 10-year absence, with first equine outbreak detected in Campania region in a 7-year-old horse showing progressive neurological signs
- •Virus was detected in multiple tissues (heart, brain, gut, liver, spleen) by RT-PCR with 98% nucleotide identity to a strain isolated from a raptor 2 years prior in the same area
- •Evidence suggests silent viral circulation for 2 years with no positive samples detected in horses, birds, or mosquitoes during the eclipse period
- •Climate change is altering WNV epidemiology, enabling viral re-establishment in previously low-risk areas with sporadic clinical cases emerging after extended latency periods