Understanding Equine Herpesvirus (EHV)

Equine herpesvirus (EHV), commonly referred to as equine rhinopneumonitis, is a group of highly contagious viruses that affect horses worldwide. Of the nine identified strains, EHV-1, EHV-3, and EHV-4 present the greatest concern for horses in the United States. While these viruses can cause serious illness in horses, they do not pose a risk to people.

EHV Strains and Their Impact

EHV-1 is the most significant strain, known for causing upper respiratory disease and abortions or stillbirths in pregnant mares. In some cases, it can develop into equine herpes myeloencephalopathy (EHM), a severe and sometimes fatal neurological condition.

EHV-3 is linked to coital exanthema, a venereal disease affecting the reproductive tract.

EHV-4 primarily affects foals with respiratory illness and can occasionally cause abortion or neurological symptoms. Horses infected with EHV that do not progress to EHM typically recover without lasting complications.

Clinical Signs to Watch For

Clinical signs of EHV can vary widely. Some horses show no symptoms, while others may display:

• Fever

• Nasal discharge or coughing

• Depression or lethargy

• Difficulty urinating

• Loss of tail tone

• Stumbling or hind-limb weakness that may progress to all limbs

• In severe cases, an inability to rise

• Abortion in pregnant mares

How EHV Spreads

EHV-1 and EHV-4 spread easily through nose-to-nose contact, contaminated equipment such as buckets, tack, and grooming tools, and respiratory secretions in shared spaces like stalls or barns. Aborted fetuses and placental tissues can also contain high viral loads.

EHV-3 spreads through breeding or contaminated breeding equipment.

Prevention and Biosecurity

Prevention relies heavily on diligent management. Vaccination is recommended to reduce the severity of respiratory illness and lower the risk of abortion, especially in breeding programs. While current vaccines help reduce symptoms and viral shedding, they are not effective against the neurologic form, EHM.

New or returning horses should be isolated for at least 21 days and monitored closely for signs of illness. Pregnant mares and mares with foals should be housed separately and kept away from recently traveled horses.

Daily hygiene is essential. Buckets, tack, grooming tools, mucking equipment, and shared items should be cleaned and disinfected regularly. Tack and equipment should never be shared at shows or boarding facilities without proper sanitation.

Treatment and Recovery

Most horses recover with supportive care, including anti-inflammatory medications and IV fluids when needed. Severe neurological cases may require hospitalization and advanced veterinary treatment.

Source

Information provided by the U.S. Department of Agriculture.

Photo by Stefan Lafrentz