Equine Herpesvirus (Rhinopneumonitis) in Horses

EHV is highly infectious. It is transmitted between in-contact horses and can even spread between horses as they are handled by humans. Due to the highly contagious nature of EHV, affected horses must be isolated immediately. Strict observation of good biosecurity practices helps prevent EHV as well as other infectious diseases.

In most cases, EHV-1 and EHV-4 remain dormant in infected horses. These horses carry the virus in an inactive state and can infect other horses they come in contact with.

Horses with poor prognoses and/or the neurological form of EHV are often euthanized. It might take months for a horse to recover from the neurological form and in most cases there are long-term neurologic deficits.

EHV is highly contagious and can affect any horse. In foals, outbreaks of respiratory disease occur annually due to a strain of EHV-1, and in mares, EHV-4 can lead to abortion 2 to 12 weeks after infection. Being an extremely contagious infection, it is common to have seasonal outbreaks in big stables where many horses live.

In severe cases, it might develop into quadriplegia and death.

The cause of EHV is a highly contagious viral infection.

The respiratory form (rhinopneumonitis) is the most common.

It is impossible to diagnose equine herpesvirus based on clinical signs alone, as they are indistinguishable from other respiratory diseases. A correct diagnosis is only reached with a PCR test or by isolating the virus in samples taken with a nasal swab or a blood sample.

PCR testing also helps to differentiate between the neuropathological strain and other forms of the infection.

It is impossible to diagnose equine herpesvirus based on clinical signs alone, as they are indistinguishable from other respiratory diseases. A correct diagnosis is only reached with a PCR test or by isolating the virus in samples taken with a nasal swab or a blood sample.

PCR testing also helps to differentiate between the neuropathological strain and other forms of the infection.

Quarantine of symptomatic horses is critical to prevent larger outbreaks in a herd. Strategies include:

• Avoiding nose-to-nose contact with unfamiliar horses
• No sharing of buckets between horses
• Quarantining all new arrivals for a minimum of 2 weeks

It is impossible to completely prevent EHV infections. Vaccines decrease the severity of symptoms and help minimize the risk of contracting the virus. Vaccinations must be administered according to veterinary recommendations to maximize efficacy, but even appropriately administered vaccines do not protect against the neurologic form of EHV.

Isolation of affected horses is necessary for about 21 days. Aborted fetuses must be removed immediately as they are highly contagious.

It is recommended to avoid stressing the herd as sometimes a latent infection might re-emerge in stressful conditions. It is imperative to wash carefully after handling infected horses as the virus can spread to horses through people’s hands and clothing.

EHV-1 and EHV-4 are the most common forms of equine herpesvirus.

• Isolation
• Nursing care
• Medication
• Vaccination
• Stall rest