Multifocal outbreak of equine influenza in vaccinated horses in Argentina in 2018: Epidemiological aspects and molecular characterisation of the involved virus strains.
Authors: Olguin-Perglione C, Vissani M A, Alamos F, Tordoya M S, Barrandeguy M
Journal: Equine veterinary journal
Summary
# Equine Influenza Vaccine Breakdown in Argentina: A Field Evidence Study Between March and July 2018, Argentina experienced a multifocal outbreak of equine influenza affecting vaccinated horses, prompting investigation into the viral genetics and vaccine efficacy. Researchers isolated equine influenza virus (EIV) from nasopharyngeal swabs using real-time RT-PCR and performed phylogenetic analysis of the haemagglutinin and neuraminidase genes, comparing circulating strains against OIE-recommended vaccine components and those used in Argentine vaccines. All outbreak isolates belonged to the H3N8 subtype within the Florida clade 1 lineage, but phylogenetic analysis revealed multiple amino acid substitutions—including changes at antigenic sites—that differentiated field strains from vaccine strain components. Notably, 76% of affected horses had received vaccination with the most commonly used vaccine in Argentina, providing field evidence of vaccine breakdown despite regular vaccination protocols. These findings underscore the necessity for veterinarians and stud managers to ensure vaccines are updated in line with OIE recommendations and to implement rigorous quarantine and movement restrictions when disease is suspected, as antigenic drift continues to outpace current vaccine formulations.
Read the full abstract on PubMed
Practical Takeaways
- •Vaccination alone is insufficient protection against equine influenza in your practice—regular vaccination combined with quarantine and movement restrictions for respiratory disease are essential
- •When influenza-like disease occurs in vaccinated horses, consider vaccine strain mismatch as a cause and report cases to identify circulating variants that may require updated vaccines
- •Stay informed about OIE vaccine strain recommendations and coordinate with your veterinarian to ensure your facility uses current vaccine formulations, as antigenic drift occurs continuously
Key Findings
- •A multifocal H3N8 equine influenza outbreak occurred in Argentina between March-July 2018 in 76% vaccinated horses, indicating vaccine breakdown
- •Phylogenetic analysis identified all outbreak viruses as Florida clade 1, but with multiple amino acid substitutions at antigenic sites compared to vaccine strains
- •The circulating virus showed significant antigenic drift from the OIE-recommended vaccine strain and vaccine components used in Argentina
- •Real-time RT-PCR and serological testing confirmed equine influenza virus infection despite vaccination, demonstrating inadequate vaccine-strain matching