Investigation of an Outbreak of Equine Herpesvirus-1 Myeloencephalopathy in a Population of Aged Working Equids.

This study investigates an outbreak of the equine herpesvirus-1 myeloencephalopathy (EHM) disease in a group of aged horses and its link to the introduction of new horses and common living conditions. The research discusses the treatment used and the response in terms of antibodies, noting that the disease can be managed on-site when hospital referral is not possible.

Context and Objective of the Study

• The study was aimed at investigating an outbreak of EHM, a neurologic disease caused by equine herpesvirus-1 (EHV-1), in a group of aged horses.
• The outbreak happened after the introduction of five new horses, and it quickly spread amongst the horses that were grouped in two pens, consuming water and food from shared troughs.

Outbreak and Symptomatic Observation

• The outbreak was severe and swift; 42.4% of the horses showed neurological deficits within the first week.
• Along with EHM, four additional horses showed symptoms of fever and respiratory signs indicative of EHV-1 infection, while fifteen horses did not exhibit any symptoms.
• EHM was confirmed with the detection of EHV-1 N in the blood and nasal secretions of the affected horses.

Management and Treatment

• All horses were managed onsite, with EHM and EHV-1 positive horses given a combination of antiherpetic, anti-inflammatory, and antithrombotic drugs.
• Of the horses that developed EHM, around 42.9% had to be euthanized due to severe symptoms, such as recumbency (inability to get up) and extreme vestibular signs (indicative of a problem with balance).

Impact on Immunity: Antibody Levels

• The acute serum samples showed no significant difference in the Anti-EHV-1 total IgG and IgG 4/7 levels among the three disease groups. This means that the initial immune response did not vary significantly between the different groups of horses.
• However, when compared to the convalescent serum samples, a significant increase in antibody levels was observed for EHM and EHV-1 affected horses. This shows the body’s increased immune response to the EHV-1 infection over time.

Final Observations

• The study emphasizes the rapidity of EHM outbreak and the high fatality rate in an aged population of horses, especially under shared penning and feeding conditions.
• The research also suggests that with appropriate treatment, EHM cases can be effectively managed on the field without the need for hospital referral.