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The Veterinary record2026; doi: 10.1002/vetr.71223

Equine viral arteritis in horses undergoing pre-export testing in Spain (2016-2023): Seroprevalence estimates and diagnostic performance of a commercial indirect ELISA.

Abstract: Equine viral arteritis (EVA) is a contagious disease that affects equine reproduction and international trade. Despite its importance, epidemiological data from Spain are limited. This study aimed to assess EVA seroprevalence and evaluate the diagnostic performance of a commercial ELISA in horses before export. Methods: From 2016 to 2023, 5000 serum samples from horses across 16 Spanish autonomous communities were tested using a commercial indirect ELISA. Samples with inconclusive results, or those submitted with specific requests, underwent virus neutralisation testing (VNT). Diagnostic performance was assessed using receiver operating characteristic curve analysis and the kappa coefficient. Results: The apparent seroprevalence was 13.3% (664/5000), and the Rogan-Gladen-adjusted seroprevalence was 2.3%. Apparent seroprevalence decreased over time, and adjusted estimates reached 0.0% from 2020 onwards. ELISA showed 98.9% sensitivity and 88.7% specificity, with substantial agreement with the VNT (κ = 0.68). Seroprevalence increased with age and was highest in Andalusia and Castile and Leon. Conclusions: The study included only horses undergoing pre-export testing and was dominated by Spanish purebred horses; therefore, findings may not represent the wider Spanish equine population. Conclusions: The declining EVA seroprevalence among horses undergoing pre-export testing may reflect improved control measures. ELISA may be suitable for pre-export screening, with VNT confirmation recommended for values above 37.14%.
© 2026 British Veterinary Association.
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Publication Date: 2026-09-30 PubMed ID: 42816161DOI: 10.1002/vetr.71223Google Scholar: Lookup
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Summary

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Overview

  • This study investigated the prevalence of equine viral arteritis (EVA) in horses being tested before export in Spain between 2016 and 2023.
  • It also evaluated the effectiveness of a commercial indirect ELISA test in diagnosing EVA, comparing it with a virus neutralisation test (VNT).

Background

  • Equine viral arteritis (EVA) is a contagious viral disease affecting horses, particularly their reproductive systems.
  • EVA can hinder international trade due to restrictions imposed on infected equines.
  • Despite EVA’s significance, there has been limited epidemiological data from Spain, making it difficult to understand its prevalence and control status within the country.
  • Effective pre-export diagnostic testing is crucial to prevent the spread of EVA across borders.

Study Objectives

  • Estimate the seroprevalence (the proportion of horses with antibodies indicating past or current infection) of EVA among horses undergoing pre-export testing in Spain.
  • Assess the diagnostic performance of a commercial indirect ELISA (enzyme-linked immunosorbent assay) in detecting EVA antibodies by comparing it with the reference standard, virus neutralisation testing (VNT).

Methods

  • Sample Collection:
    • 5000 serum samples were collected from horses across 16 autonomous communities in Spain over the period 2016 to 2023.
    • The samples were primarily from Spanish purebred horses undergoing pre-export testing, which could influence representativeness.
  • Testing:
    • Each sample was tested using a commercial indirect ELISA designed to detect antibodies against EVA.
    • Samples with inconclusive ELISA results or submitted with specific requests also underwent virus neutralisation testing (VNT), considered the gold standard for EVA diagnosis.
  • Data Analysis:
    • Seroprevalence was reported as both apparent prevalence (directly from ELISA results) and adjusted prevalence using Rogan-Gladen correction to account for test sensitivity and specificity.
    • Diagnostic performance was evaluated using receiver operating characteristic (ROC) curve analysis to determine sensitivity and specificity.
    • The agreement between ELISA and VNT results was calculated using Cohen’s kappa coefficient (κ).

Key Results

  • Seroprevalence:
    • Overall apparent seroprevalence was 13.3% (664 out of 5000 horses tested positive via ELISA).
    • After adjustment for test accuracy, the seroprevalence was estimated to be 2.3%.
    • The adjusted seroprevalence declined over the study period, reaching 0.0% from 2020 onwards, suggesting a sharp reduction or elimination of infection in tested horses.
    • Seroprevalence was higher in older horses, indicating possible increased cumulative exposure with age.
    • Geographical variation showed higher seroprevalence in Andalusia and Castile and Leon regions.
  • Diagnostic Performance of ELISA:
    • Sensitivity (ability to detect true positives) was 98.9%, indicating very few false negatives.
    • Specificity (ability to detect true negatives) was 88.7%, indicating some false positives may occur.
    • Substantial agreement between ELISA and VNT was observed with a kappa coefficient of 0.68, suggesting the ELISA is reliable but not perfect.
    • The study identified an ELISA cutoff value of 37.14%, above which VNT confirmation is recommended to reduce false positive results.

Interpretation and Implications

  • The decline in EVA seroprevalence over time, particularly reaching zero after 2020 in pre-export tested horses, likely reflects successful control measures in Spain, such as vaccination, biosecurity, or selective breeding policies.
  • The high sensitivity and substantial agreement with VNT make the commercial indirect ELISA a practical screening tool for EVA in pre-export settings.
  • However, because specificity is less than 100%, samples with ELISA values exceeding 37.14% should be confirmed by VNT to avoid unnecessary trade restrictions due to false positives.
  • Limitation: Results may not generalize to all horses in Spain as the sample was limited to those undergoing pre-export testing and was dominated by purebred horses.
  • Recommendations include using ELISA as a first-line screening test combined with selective VNT confirmation to balance cost and diagnostic accuracy in international trade contexts.

Summary

  • This large-scale study provided valuable epidemiological data on EVA in Spain, showing reduced virus circulation in export-tested horses over recent years.
  • The commercial indirect ELISA proves to be an effective screening test, especially when combined with confirmatory testing at defined cutoff points.
  • These findings support ongoing surveillance and tailored testing protocols to maintain Spain’s equine trade while preventing EVA spread.

Cite This Article

APA
Gago P, Dorrego A, Pozo P, Raez A, Rivera B, de Juan L, Cruz-Lopez F. (2026). Equine viral arteritis in horses undergoing pre-export testing in Spain (2016-2023): Seroprevalence estimates and diagnostic performance of a commercial indirect ELISA. Vet Rec. https://doi.org/10.1002/vetr.71223

Publication

The Veterinary record
ISSN: 2042-7670
NlmUniqueID: 0031164
Country: England
Language: English

Researcher Affiliations

Gago, Paloma
  • VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain.
  • Department of Animal Health, Faculty of Veterinary Medicine, Universidad Complutense de Madrid, Madrid, Spain.
Dorrego, Abel
  • VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain.
Pozo, Pilar
  • VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain.
Raez, Alejandra
  • VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain.
Rivera, Belen
  • VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain.
de Juan, Lucía
  • VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain.
  • Department of Animal Health, Faculty of Veterinary Medicine, Universidad Complutense de Madrid, Madrid, Spain.
Cruz-Lopez, Fatima
  • VISAVET Health Surveillance Centre, Universidad Complutense de Madrid, Madrid, Spain.

Grant Funding

  • CT82/20-CT83/20 / Universidad Complutense de Madrid-Banco Santander Predoctoral contracts for researchers in training

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