Whole genome sequencing and phylogenetic analysis of the equine infectious anemia virus associated with 2017 Spain outbreaks

Sep 30, 2026

2017 marked the first equine infectious anemia virus (EIAV) outbreak in Spain in 34 years, involving three horses from two epidemiologically unrelated holdings. Whole-genome and gag-gene phylogenetic analyses showed the Spanish EIAV strains formed a distinct monophyletic clade with >99% nucleotide identity, consistent with a common contamination event. The strains also clustered with North American lineages, sharing up to 80.12% identity, notably with the Wyoming strain, suggesting an unprecedented European association. The results emphasize possible introduction routes and the need for enhanced EIAV surveillance and genomic characterization to clarify transmission dynamics.

LanguageEnglish

CategoryResearch & Report

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Pages8

Reading Time20 min

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Summary

Introduction

EIAV characteristics and genome organization

Transmission routes and clinical manifestations

Wiernasz etal. BMC Veterinary Research (2026) 22:10 [https://doi.org/10.1186/s12917-025-05100-4](https://doi.org/10.1186/s12917-025-05100-4) BMC Veterinary Research RESEARCH Open Access Whole genome sequencing and phylogenetic analysis of the equine infectious anemia virus associated with 2017 Spain outbreaks N. Wiernasz1†, A. Deshiere1†, M. Agüero2, E. Garcia3, [R. de](R. de) la Haza3, G. Cáceres 3, F. Touzain4, Y. Blanchard4, F. Lecouturier 1, D. Froger 1,6, N. Berthet5, A. Hans 1 and J. C. Valle-Casuso 1,6* Summary In 2017, Spain reported its first equine infectious anemia virus (EIAV) outbreak in 34 years, affecting three horses in two unrelated holdings in Candeleda (Ávila) and Serradilla (Cáceres), with no apparent epidemiological link between premises. Phylogenetic analysis of whole genome and the gag gene revealed that the Spanish EIAV strains form a distinct monophyletic clade, sharing more than 99% nucleotide identity, suggesting a common contamination event. Interestingly, these three viral strains seem to cluster with North American strains, sharing up to 80. 12% nucleotide identity, notably with the Wyoming strain, marking the first such association for Europeanstrains. These findings raise important questions regarding the potential routes of EIAV introduction into Spain and highlight the need for enhanced surveillance and genomic characterization to better understand viral transmission dynamics. Keywords Equine infectious anemia, Virus, Phylogeny, Horse, Spain, NGS †N. Wiernasz and A. Deshiere contributed equally to this work. *Correspondence: J. C. Valle-Casuso [Jose-carlos.valle-casuso@anses.fr](Jose-carlos.valle-casuso@anses.fr) 1ANSES-Laboratory for Animal Health in Normandy, Physiopathology and Epidemiology of Equine Diseases Unit, Goustranville, France 2Laboratorio Central de Veterinaria (LCV), Ministry of Agriculture, Fisheries and Food, Madrid, Spain 3Ministry of Agriculture, Fisheries and Food, Subdirección General de Sanidad E Higiene Animal y Trazabilidad, Madrid, Spain 4ANSES-Laboratoire de Ploufragan-Plouzané-Niort, GVB Unit, Ploufragran 22440, France 5Institut Pasteur, Unité Environnement Et Risques Infectieux, Cell uled’Intervention Biologique d’Urgence, Paris, France 6Mixed Technological Unit“Equine Health and Welfare—Organisation and Traceability of the Equine Industry”(UMT SABOT), , 14430 Goustranville, France Introduction Equine infectious anemia virus (EIAV) causes a lifelong persistent infection specifically infecting equids (horses, ponies, zebras, mules and donkeys) which is notifiable to the World Organization for Animal Health (WOAH) and European Union. Like Human Immunodeficiency Virus (HIV), EIAV is a retrovirus belonging to the lentivirus genus [17], characterized by its high genetic variability and ability to establish latent infections. Despite a major effort to characterize and sequence full-length EIAV genomes during the last decades, only a limited number of sequences from North and South America, Europe and Asia are available [5, 8, 9, 23]. EIAV’s genome is a diploid, single stranded RNA molecule of approximately 8.2 kb, flanked at its 5’ and 3’ termini by identical long terminal repeat (LTR) regions. It contains three major open reading frames: gag (group specific antigen), pol (polymerase) and env (envelope), that encode the capsid proteins, the © The Author(s) 2025. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this articl

FAQs

What did the whole-genome and gag-gene phylogenetic analyses reveal about the 2017 Spanish EIAV strains?

They formed a distinct monophyletic clade with more than 99% nucleotide identity, indicating a common contamination event.

How were the three affected horses epidemiologically related?

They were in two unrelated holdings and showed no apparent epidemiological link between premises.

What is the significance of the clustering with North American strains, including the Wyoming strain?

It suggests the Spanish strains share an unexpected association with North American lineages, raising questions about how EIAV was introduced into Spain.

Sep 30, 2026

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