The first reported Florida clade 1 virus in the Nordic countries, isolated from a Swedish outbreak of equine influenza in 2011.
Abstract: Equine Influenza Virus (EIV) is a major cause of respiratory disease in horses and the virus constantly undergoes antigenic drift. Here we characterize and describe the HA1 and the NA genes of H3N8 within samples obtained from outbreaks in Sweden during November-December 2011. Both clade 1 and clade 2 viruses of the Florida sublineage were identified. The index case of clade 2 was transported to Sweden from Spain through the Netherlands, whereas the clade 1 had its origin from a Swedish stud farm. The clade 1 virus was efficiently spread between training yards by unvaccinated young horses, but vaccinated horses were also presented with clinical signs of respiratory disease. No virus of the Eurasian lineage was isolated during this outbreak. Clade 1 has previously been described in outbreaks in numerous of other countries, but this is the first time it has been detected in Sweden. The results from this study shows the importance of including both clade 1 and clade 2 of the Florida sublineage in equine influenza vaccines, supporting the ESP and OIE recommendations.
Copyright © 2016. Published by Elsevier B.V.
Publication Date: 2015-12-21 PubMed ID: 26854337DOI: 10.1016/j.vetmic.2015.12.010Google Scholar: Lookup
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- Journal Article
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Summary
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This study explores the first reported occurrence of the Florida Clade 1 virus, a form of Equine Influenza Virus (EIV), in the Nordic countries using samples from a Swedish outbreak in 2011. The researchers assert the importance of incorporating both Clade 1 and Clade 2 of the Florida sublineage in EIV vaccines, in line with ESP and OIE recommendations.
Equine Influenza Virus (EIV) Classification
- The study focuses on the H3N8 strain of EIV, a contagious virus that results in respiratory disease among horses. This virus is known to constantly evolve and change — a process known as antigenic drift.
- Specifically, the researchers examined the HA1 and the NA genes of H3N8 from samples taken during Swedish outbreaks in November and December 2011.
- This research found the presence of both Clade 1 and Clade 2 viruses of the Florida sublineage, a classification further refining the H3N8 strain. This sublineage has been detected in many other countries, but this is the first recorded instance in Sweden.
Origins of the Virus
- The study traced the origins of the Clade 2 index case to Spain, believed to have been transported to Sweden via the Netherlands.
- In contrast, the Clade 1 version was initially found in a Swedish stud farm, indicating a local origin.
Clinical Findings and Implications for Vaccination
- Transmission of the Clade 1 virus occurred largely through unvaccinated young horses between training yards, indicating its high infection rate.
- However, some vaccinated horses showed clinical signs of respiratory disease as well, suggesting the current vaccines’ limited effectiveness against this variant.
- The study did not detect any traces of the virus of the Eurasian lineage during the outbreak.
- These findings highlight the necessity for EIV vaccines to include antigens for both Clade 1 and Clade 2 of the Florida sublineage. This aligns with recommendations from the European Surveillance Programme for Veterinary Antimicrobial Consumption (ESVAC) and the World Organisation for Animal Health (OIE).
Cite This Article
APA
Back H, Berndtsson LT, Gröndahl G, Ståhl K, Pringle J, Zohari S.
(2015).
The first reported Florida clade 1 virus in the Nordic countries, isolated from a Swedish outbreak of equine influenza in 2011.
Vet Microbiol, 184, 1-6.
https://doi.org/10.1016/j.vetmic.2015.12.010 Publication
Researcher Affiliations
- Department of Virology, Immunobiology and Parasitology, National Veterinary Institute, Uppsala, Sweden. Electronic address: helena.back@mpa.se.
- Department of Virology, Immunobiology and Parasitology, National Veterinary Institute, Uppsala, Sweden.
- Department of Animal Health and Antimicrobial Strategies, National Veterinary Institute, Uppsala, Sweden.
- Department of Disease Control and Epidemiology, National Veterinary Institute, Uppsala, Sweden.
- Department of Clinical Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden.
- Department of Virology, Immunobiology and Parasitology, National Veterinary Institute, Uppsala, Sweden.
MeSH Terms
- Animals
- Antigens, Viral / genetics
- Disease Outbreaks / veterinary
- Dogs
- Hemagglutinin Glycoproteins, Influenza Virus / genetics
- Horse Diseases / epidemiology
- Horse Diseases / virology
- Horses
- Influenza A Virus, H3N8 Subtype / classification
- Influenza A Virus, H3N8 Subtype / genetics
- Influenza A Virus, H3N8 Subtype / isolation & purification
- Influenza Vaccines / standards
- Madin Darby Canine Kidney Cells
- Neuraminidase / genetics
- Phylogeny
- Sweden
- Travel
- Vaccination / standards
- Vaccination / veterinary
Citations
This article has been cited 8 times.- Ahmed BM, Bayoumi MM, Farrag MA, Elgamal MA, Daly JM, Amer HM. Emergence of equine influenza virus H3Nx Florida clade 2 in Arabian racehorses in Egypt. Virol J 2022 Nov 12;19(1):185.
- Blanco-Lobo P, Rodriguez L, Reedy S, Oladunni FS, Nogales A, Murcia PR, Chambers TM, Martinez-Sobrido L. A Bivalent Live-Attenuated Vaccine for the Prevention of Equine Influenza Virus. Viruses 2019 Oct 11;11(10).
- Singh RK, Dhama K, Karthik K, Khandia R, Munjal A, Khurana SK, Chakraborty S, Malik YS, Virmani N, Singh R, Tripathi BN, Munir M, van der Kolk JH. A Comprehensive Review on Equine Influenza Virus: Etiology, Epidemiology, Pathobiology, Advances in Developing Diagnostics, Vaccines, and Control Strategies. Front Microbiol 2018;9:1941.
- Gildea S, Garvey M, Lyons P, Lyons R, Gahan J, Walsh C, Cullinane A. Multifocal Equine Influenza Outbreak with Vaccination Breakdown in Thoroughbred Racehorses. Pathogens 2018 Apr 17;7(2).
- Gahan J, Garvey M, Gildea S, Gür E, Kagankaya A, Cullinane A. Whole-genome sequencing and antigenic analysis of the first equine influenza virus identified in Turkey. Influenza Other Respir Viruses 2018 May;12(3):374-382.
- Junkkari R, Mykkänen A, Sulku P, Rantala M, Pohjanvirta T, Eklund M, Pelkonen S, Grönthal T. Occurrence, antibiotic susceptibility and genetic variation of Streptococcus zooepidemicus in Finnish weanling horses with and without respiratory infection. Acta Vet Scand 2026 Jan 27;68(1):7.
- Cullinane A, Garvey M, Dayot L, Lukaseviciute G. Equine Rotavirus A Outbreaks in Ireland (2023-2024): An Epidemiological Investigation and Virus Genotyping. Viruses 2025 Mar 31;17(4).
- Branda F, Yon DK, Albanese M, Binetti E, Giovanetti M, Ciccozzi A, Ciccozzi M, Scarpa F, Ceccarelli G. Equine Influenza: Epidemiology, Pathogenesis, and Strategies for Prevention and Control. Viruses 2025 Feb 21;17(3).
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