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Animals : an open access journal from MDPI2025; 15(16); 2344; doi: 10.3390/ani15162344

First Equine Herpes Myeloencephalopathy (EHM) Outbreak in Chile.

Abstract: Equine herpes myeloencephalopathy (EHM) is a neurological disease in horses caused by Equine herpesvirus type 1 (EHV-1). It is a serious condition, often resulting in severe neurological deficits, and can be fatal. In this report, we discuss the first outbreak of EHM in Chile (clinical signs, epidemiology, diagnosis, and control measures). A total of 567 polo horses were kept at the facility: 58.4% mares, 41.6% geldings, and stallions. Mean age was 9.7 ± 0.132 years. Thirteen horses showed clinical signs of EHV-1, eight had fevers (1.4%), and eleven developed EHM (1.9%). Only six of the eleven EHM cases had high fevers (>39.5 °C). Mortality was 0.35% (index case and one additional case) and morbidity reached 3.35% (19/567). PCR testing was performed on 214 horses (37.7%); 13 tested positive (6.1%) and 201 negative (93.9%). Of PCR-positive horses, 53.8% showed clinical signs. Notably, 2.9% of PCR-negative horses also presented signs compatible with EHV-1. CT values among positive cases ranged from 30 to 39. This first EHM outbreak in Chile showed low morbidity and mortality. Rapid implementation of strict quarantine and biosecurity effectively limited spread. Further data on viral prevalence and types are needed to improve preparedness.
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Publication Date: 2025-08-11 PubMed ID: 40867672PubMed Central: PMC12382900DOI: 10.3390/ani15162344Google 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.

Equine herpes myeloencephalopathy (EHM) is a neurological disease in horses caused by equine herpesvirus type 1 (EHV-1). This study reports the first outbreak of EHM in Chile, describing the clinical signs, diagnosis, epidemiology, and control measures taken during the incident.

Background and Importance

  • EHM is caused by Equine herpesvirus type 1 (EHV-1), affecting the nervous system of horses.
  • The disease can lead to severe neurological symptoms and sometimes death.
  • This report documents the first known EHM outbreak in Chile, which is significant for veterinary and animal health communities in the region.

Population and Study Setting

  • The outbreak occurred in a facility housing 567 polo horses.
  • Population consisted of 58.4% mares, 41.6% geldings and stallions combined.
  • The average age of horses was approximately 9.7 years.

Clinical Presentation and Morbidity

  • Thirteen horses exhibited clinical signs typical of EHV-1 infection.
  • Eight horses (1.4%) developed fevers, and eleven horses (1.9%) developed neurological signs consistent with EHM.
  • Among those with EHM, six had high fevers (>39.5 °C), indicating fever is not always present or severe in EHM.
  • Morbidity, defined as the proportion showing disease signs, was 3.35% (19 of 567 horses).
  • Mortality was low at 0.35%, with two horses dying (including the index case).

Diagnostic Testing and Results

  • Polymerase chain reaction (PCR) testing for EHV-1 was performed on 214 horses (about 38% of the population).
  • Of these, 13 horses (6.1%) tested positive, and 201 (93.9%) tested negative.
  • Among PCR-positive horses, 53.8% showed clinical signs, demonstrating some infected horses were asymptomatic or subclinical.
  • Interestingly, 2.9% of PCR-negative horses also exhibited signs compatible with EHV-1, suggesting possible false negatives or alternative diagnoses.
  • Cycle threshold (CT) values in PCR-positive horses ranged between 30 and 39, indicating a low to moderate viral load.

Control Measures and Outcomes

  • Rapid implementation of strict quarantine and biosecurity protocols was crucial to limiting the outbreak’s spread within the facility.
  • Despite the presence of EHM, morbidity and mortality remained relatively low, highlighting the effectiveness of timely interventions.
  • The outbreak underscores the need for vigilance and preparedness against EHV-1 in regions where it has not been previously reported.

Conclusions and Future Perspectives

  • This first recorded outbreak of EHM in Chile provides valuable epidemiological and clinical insights.
  • It stresses the importance of rapid diagnosis, quarantine, and biosecurity in controlling viral outbreaks among horses.
  • The study calls for further research to obtain more comprehensive data on the prevalence and viral strains of EHV-1 in Chile.
  • Such data will improve risk assessment, surveillance, and response strategies in the future.

Cite This Article

APA
Durán MC, Suazo M, Maturana A, Vargas MP, García A, Ahumada C, Pezoa A, Goehring LS, Lara F. (2025). First Equine Herpes Myeloencephalopathy (EHM) Outbreak in Chile. Animals (Basel), 15(16), 2344. https://doi.org/10.3390/ani15162344

Publication

Animals : an open access journal from MDPI
ISSN: 2076-2615
NlmUniqueID: 101635614
Country: Switzerland
Language: English
Volume: 15
Issue: 16
PII: 2344

Researcher Affiliations

Durán, María Carolina
  • Unidad Medicina y Cirugía Equina, Escuela Medicina Veterinaria, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Camino Lo Pinto Km 2,5 Colina, Santiago 9340000, Chile.
Suazo, Macarena
  • Unidad Medicina y Cirugía Equina, Escuela Medicina Veterinaria, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Camino Lo Pinto Km 2,5 Colina, Santiago 9340000, Chile.
Maturana, Antonia
  • Unidad Medicina y Cirugía Equina, Escuela Medicina Veterinaria, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Camino Lo Pinto Km 2,5 Colina, Santiago 9340000, Chile.
Vargas, María Paz
  • Private Practitioner, Santiago 7591110, Chile.
García, Alfonso
  • Laboratorios de Sanidad Animal, Departamento Red SAG de Laboratorios, Servicio Agrícola Ganadero, Santiago 7500007, Chile.
Ahumada, Carolyn
  • Laboratorios de Sanidad Animal, Departamento Red SAG de Laboratorios, Servicio Agrícola Ganadero, Santiago 7500007, Chile.
Pezoa, Alexza
  • Laboratorios de Sanidad Animal, Departamento Red SAG de Laboratorios, Servicio Agrícola Ganadero, Santiago 7500007, Chile.
Goehring, Lutz S
  • Department of Veterinary Science, Gluck Equine Research Center, University of Kentucky, 1400 Nicholasville Rd., Lexington, KY 40546, USA.
Lara, Felipe
  • Unidad Medicina y Cirugía Equina, Escuela Medicina Veterinaria, Facultad de Ciencias de la Vida, Universidad Andrés Bello, Camino Lo Pinto Km 2,5 Colina, Santiago 9340000, Chile.

Grant Funding

  • Funding is only for publication purposes / Universidad Andres Bello

Conflict of Interest Statement

The authors declare no conflicts of interest.

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