Evidence for current circulation of an ancient West Nile virus strain (NY99) in Brazil

Area of Science:

• Veterinary Virology
• Arbovirology
• Molecular Epidemiology

Background:

• West Nile virus (WNV) first detected in Brazil in 2018 in horses with neurological disease.
• WNV is an emerging zoonotic arbovirus with significant public health and veterinary implications.
• Neurological disease in equids can be an indicator of WNV circulation in a region.

Purpose of the Study:

• To report the first confirmed case of WNV infection in a horse from Ceará state, Brazil.
• To present the complete genome sequence of a WNV isolate from Espírito Santo state, Brazil.
• To investigate the genetic lineage and potential origin of the circulating WNV strain in Brazil.

Main Methods:

• Isolation of WNV from equine tissues (brain, spinal cord) of a neurologically affected horse.
• Next-generation sequencing (MiSeq) for complete genome sequencing of the WNV isolate.
• Phylogenetic analysis using established WNV genome sequences to determine lineage and relationships.

Main Results:

• The first WNV case in a horse from Ceará state was identified in 2019.
• The WNV isolate from Espírito Santo state belongs to lineage 1a.
• Phylogenetic analysis indicated the Brazilian isolate clusters with the historical NY99 strain, not seen in the USA since 2005.

Conclusions:

• The findings support the hypothesis of long-term, silent circulation of West Nile virus in Brazil.
• The genetic profile of the WNV isolate suggests introductions from sources with historical WNV activity.
• Continued surveillance of WNV in animal populations is crucial for understanding its epidemiology in Brazil.