The following information is provided as a client handout from the Bayer Agriculture Division. Copyright 1997 Bayer Corporation.

This equine herpesvirus causes abortion, stillbirths, and weak foals that die soon after birth. EHV-1 also causes respiratory disease in young horses and very mild respiratory infections in older horses. Often the respiratory signs are so mild in pregnant mares that they go unnoticed, and the first sign that anything is wrong is an abortion or the birth of a fatally ill, live foal.

Neurologic disease leading to paralysis and possible death is a relatively rare condition that also may result from infection with EHV-1. The nervous syndrome generally follows the respiratory syndrome by one to two weeks.

Clinical Signs

Abortion "storms" on breeding farms are the most feared clinical syndrome due to EHV-1. Affected mares have generally shown no clinical signs before the abortion occurs. Most EHV-1 abortions occur in the last trimester of pregnancy. They may occur up to three months after the respiratory phase of the disease, which often goes unnoticed by the owner or handler. Aborted fetuses or stillborn foals are not decomposed. Near-term foals may be born alive but succumb to fulminating pneumonia within a few days.

Diagnosis

A diagnosis of EHV-1 abortion can only be made by postmortem examination of the fetus. Virus can be detected in foal tissues by special histological procedures and staining. Testing the mare's serum for antibodies is of no value, because virus-infected foals can be born from mares that show no evidence of recent antibody activity, and noninfected foals can be born from dams that do show recent antibody rises.

Treatment

There is no specific therapy for EHV-1 respiratory or neurologic disease, or for abortion or weak foals. Rest, supportive care, and antibiotics for secondary infections will help horses come through the disease with the least amount of damage. Early recognition of respiratory infection and viral abortion is essential to preventing an outbreak of disease on the premises. It is also important to recognize individual cases early and immediately stop work or training of affected horses.

Prevention

Vaccination of all horses on a farm is very important to contain outbreaks of EHV-1. Although vaccination may not entirely suppress infection, it will reduce the severity of disease and help control the spread of the infection by lowering viral shedding. Good herd management and good individual-horse management also help to reduce infection and control resulting damage. Because early respiratory infection can be difficult to detect, especially among older horses, careful observation is necessary to recognize the presence of disease. Also, if an abortion is not recognized as EHV-1-caused, then it may become the first of many abortions that follow a few weeks after the first one. In order to prevent such an abortion "storm," the fetus and all placental membranes must be placed in a waterproof container and removed (preferably sent to a diagnostic laboratory), and the area must be thoroughly cleaned and disinfected. A1I mares that have been in contact with the affected mare should be isolated for at least six weeks, as should all newly introduced horses. Handlers should take care not to spread the disease from one horse to another, either by equipment or hands.