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Viruses2024; 16(10); 1594; doi: 10.3390/v16101594

Outbreak of Western Equine Encephalitis Virus Infection Associated with Neurological Disease in Horses Following a Nearly 40-Year Intermission Period in Argentina.

Abstract: Western equine encephalitis virus (WEEV) is a mosquito-borne arbovirus (genus , family ) that has re-emerged in South America in late 2023, causing severe disease in both horses and humans after a nearly 40-year intermission period. We here describe the virological, serological, pathological, and molecular features of WEEV infection in horses during the 2023-2024 outbreak in Argentina. WEEV-infected horses developed neurological signs with mild to severe encephalitis associated with minimal to abundant WEEV-infected cells, as demonstrated by WEEV-specific in situ hybridization. The distribution of viral RNA was multifocal, with predominance within neuronal bodies, neuronal processes, and glial cells in the medulla oblongata and thalamic regions. Phylogenetic analysis of partial nsP4 sequences from three viral isolates obtained from three different provinces of Argentina support grouping with other temporally current WEEV strains from Uruguay and Brazil under a recently proposed novel lineage.
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Publication Date: 2024-10-10 PubMed ID: 39459927PubMed Central: PMC11512283DOI: 10.3390/v16101594Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

Western equine encephalitis virus (WEEV) re-emerged in Argentina in late 2023 after nearly 40 years without reported cases, causing neurological disease in horses. The study characterizes the virological, pathological, serological, and molecular aspects of this outbreak, including viral distribution in the brain and genetic relationships with other South American WEEV strains.

Background and Significance

  • Western equine encephalitis virus (WEEV) is an arbovirus transmitted by mosquitoes, belonging to the genus Alphavirus and family Togaviridae.
  • Historically, WEEV caused outbreaks in horses and humans in North and South America, with neurological diseases ranging from mild to fatal encephalitis.
  • In Argentina, WEEV infections had not been reported for nearly 40 years prior to the 2023 outbreak, making its reappearance significant for veterinary and public health surveillance.

Outbreak Description and Clinical Presentation

  • The outbreak occurred in Argentina from late 2023 into 2024, involving horses displaying neurological signs indicative of encephalitis.
  • Clinical signs in affected horses included various neurological deficits, reflecting mild to severe inflammation of the brain (encephalitis).
  • This outbreak is notable as it marks a re-emergence after a long hiatus, indicating potential ecological or epidemiological changes favoring virus transmission.

Virological and Pathological Findings

  • WEEV infection was confirmed in horses through detection of viral RNA and viral antigen in brain tissues.
  • In situ hybridization specific to WEEV revealed infected cells primarily in the medulla oblongata and thalamic regions of the brain.
  • The pattern of viral RNA distribution was multifocal, present in neuronal bodies, neuronal processes, and glial cells, indicating widespread neuronal infection.
  • The severity of encephalitis varied from minimal to abundant viral presence correlating with clinical severity.

Serological and Molecular Analyses

  • Serological testing confirmed immune responses in infected horses, supporting recent infection with WEEV.
  • Molecular analysis targeted the nsP4 gene region, a conserved part of the virus genome involved in RNA replication.
  • Partial nsP4 sequences were obtained from viral isolates collected in three distinct Argentine provinces, demonstrating geographic spread.

Phylogenetic Insights

  • Phylogenetic analysis grouped these Argentine viral isolates with recent WEEV strains from Uruguay and Brazil.
  • These isolates clustered under a newly proposed lineage of WEEV, distinct from older strains, suggesting recent evolutionary changes or introductions.
  • This lineage’s identification has implications for understanding viral evolution and epidemiology in South America.

Implications and Conclusions

  • The resurgence of WEEV after a long intermission highlights the need for ongoing surveillance of arboviruses affecting horses and humans.
  • The outbreak underscores the potential for significant neurological disease in equines associated with WEEV in Argentina and neighboring countries.
  • Molecular and phylogenetic data provide a framework for tracking virus evolution and assessing risk for future outbreaks.
  • These findings call for enhanced vector control, vaccination strategies for horses, and public health preparedness to mitigate impact on animal and human populations.

Cite This Article

APA
Vissani MA, Alamos F, Tordoya MS, Minatel L, Schammas JM, Dus Santos MJ, Trono K, Barrandeguy ME, Balasuriya UBR, Carossino M. (2024). Outbreak of Western Equine Encephalitis Virus Infection Associated with Neurological Disease in Horses Following a Nearly 40-Year Intermission Period in Argentina. Viruses, 16(10), 1594. https://doi.org/10.3390/v16101594

Publication

Viruses
ISSN: 1999-4915
NlmUniqueID: 101509722
Country: Switzerland
Language: English
Volume: 16
Issue: 10
PII: 1594

Researcher Affiliations

Vissani, María Aldana
  • Instituto de Virología, CICVyA, Instituto Nacional de Tecnología Agropecuaria (INTA), Buenos Aires B1686, Argentina.
  • Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Ciudad de Buenos Aires C1033AAJ, Argentina.
  • Escuela de Veterinaria, Facultad de Ciencias Agrarias y Veterinarias, Universidad del Salvador, Pilar B1630AHU, Argentina.
Alamos, Florencia
  • Instituto de Virología, CICVyA, Instituto Nacional de Tecnología Agropecuaria (INTA), Buenos Aires B1686, Argentina.
Tordoya, María Silvia
  • Instituto de Virología, CICVyA, Instituto Nacional de Tecnología Agropecuaria (INTA), Buenos Aires B1686, Argentina.
Minatel, Leonardo
  • Facultad de Ciencias Veterinarias, Universidad de Buenos Aires, Ciudad de Buenos Aires C1427CWN, Argentina.
Schammas, Juan Manuel
  • Instituto de Virología, CICVyA, Instituto Nacional de Tecnología Agropecuaria (INTA), Buenos Aires B1686, Argentina.
Dus Santos, María José
  • Instituto de Virología, CICVyA, Instituto Nacional de Tecnología Agropecuaria (INTA), Buenos Aires B1686, Argentina.
Trono, Karina
  • Instituto de Virología, CICVyA, Instituto Nacional de Tecnología Agropecuaria (INTA), Buenos Aires B1686, Argentina.
Barrandeguy, María E
  • Instituto Nacional de Investigación Agropecuaria (INIA), Plataforma de Investigación en Salud Animal, Estación Experimental La Estanzuela, Colonia, Uruguay.
Balasuriya, Udeni B R
  • Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
  • Louisiana Animal Disease Diagnostic Laboratory (LSU Diagnostics), School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
Carossino, Mariano
  • Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.
  • Louisiana Animal Disease Diagnostic Laboratory (LSU Diagnostics), School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803, USA.

MeSH Terms

  • Animals
  • Horses
  • Argentina / epidemiology
  • Encephalitis Virus, Western Equine / genetics
  • Phylogeny
  • Horse Diseases / virology
  • Horse Diseases / epidemiology
  • Disease Outbreaks / veterinary
  • RNA, Viral / genetics
  • Encephalomyelitis, Western Equine / virology
  • Encephalomyelitis, Western Equine / epidemiology
  • Encephalomyelitis, Equine / virology
  • Encephalomyelitis, Equine / epidemiology
  • Encephalomyelitis, Equine / veterinary
  • Nervous System Diseases / virology
  • Nervous System Diseases / veterinary
  • Nervous System Diseases / epidemiology

Grant Funding

  • NA / INTA-HARAS Agreement
  • PG009641 / School of Veterinary Medicine, Louisiana State University

Conflict of Interest Statement

The authors declare no conflict of interest.

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Citations

This article has been cited 6 times.
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