What is ehv in horses

Understanding Equine Herpesvirus

Equine herpesvirus (EHV) is a family of viral infections that affect horses worldwide. Multiple strains cause different clinical syndromes, ranging from mild respiratory symptoms to severe neurological disease. EHV is highly contagious and endemic in most horse populations, making it one of the most significant viral diseases affecting horses. Infection can occur at any age, though clinical severity often varies with age and immune status.

The virus belongs to the Herpesviridae family and is characterized by the ability to establish latency in sensory nerve ganglia, meaning infected horses become lifelong carriers. Even recovered horses may shed virus intermittently, particularly during stress or immunosuppression, making disease control challenging in multi-horse operations.

EHV Strains and Clinical Signs

EHV-1 is the most pathogenic strain and can cause respiratory disease, myeloencephalopathy (neurological disease affecting the spinal cord and brain), and abortion in pregnant mares. Respiratory signs include nasal discharge, cough, fever, and loss of appetite. Neurological signs can be severe, ranging from hindquarters weakness to complete recumbency. Abortion can occur at any stage of pregnancy, sometimes without prior signs of illness.

EHV-2 is ubiquitous in horse populations and usually causes mild or subclinical respiratory disease. Young foals may develop rhinitis (nasal inflammation) and fever. EHV-4 is highly contagious and causes primarily respiratory disease with nasal discharge, cough, and fever. EHV-3 is sexually transmitted and causes painful vesicles and ulcers on genital tissues, often followed by bacterial secondary infection. Most horses recover from EHV-3 infection without long-term complications.

Transmission and Risk Factors

EHV spreads primarily through respiratory secretions when infected horses cough or sneeze. Direct contact with infected horses, their respiratory secretions, or blood can transmit infection. The virus survives briefly on equipment, clothing, and hands, making indirect transmission possible through contaminated grooming equipment, saddles, blankets, and other fomites. Sharing water troughs and feed buckets poses additional transmission risk.

Risk factors for infection include stress (transport, competition, weather changes), young age, old age, immunosuppression, and high-density populations. Pregnant mares infected with EHV-1 face increased abortion risk. Multiple exposures to carrier horses increase infection probability in populations where the virus is endemic.

Prevention and Management

Prevention requires biosecurity measures including quarantine of new or sick horses, separate equipment for each horse, handwashing between handling horses, and limiting facility exposure. Vaccination against EHV-1 and EHV-4 is available, though vaccines provide incomplete protection and require regular boosters. No specific antiviral treatment exists; management is supportive, including rest, fluids, and treatment of secondary infections.

Horses recovering from EHV-1, particularly those with neurological disease, may take weeks to months to regain full function. Some experience permanent neurological effects. Early diagnosis through nasopharyngeal swabs, blood tests, or CSF analysis aids treatment and quarantine decisions. Careful handling and rehabilitation are essential for neurologically affected horses.