Infectious diseases

EQUINE HERPES VIRUS

IN THIS SERIES, WE’RE COVERING COMMON DISEASES THAT CAN AFFECT THE EQUINE POPULATION; HOW TO SPOT THEM, MEASURES TO TAKE TO PROTECT HORSES IN YOUR CARE, AND HOW TO PREVENT TRANSMISSION. IN PART THREE WE TALK ABOUT EQUINE HERPES VIRUS (EHV).

Although there are nine strains, Equine Herpes Virus-1 (EHV1) and Equine Herpes Virus-4 (EHV-4) are most commonly seen. Horses may suffer respiratory disease, abortion, neonatal foal death and neurological disease.

TRANSMISSION

Transmission through the air is the most common route. Viral shedding can typically last seven to ten days but can persist much longer, therefore a 28-day isolation period is recommended after diagnosis. The virus can live in the environment for a fortnight and be transmitted between horses on clothing and equipment, and in lorries and trailers.

INCUBATION TIME

May be as short as 24 hours but is typically four to six days, though may be longer.

WHAT ARE THE CLINICAL SIGNS?

Infected horses can develop complications such as secondary bacterial infections.

HOW QUICKLY DO HORSES RECOVER?

This varies depending on severity of clinical signs and whether the horse has secondary infections.

HOW LONG MUST THE MOVEMENT OF HORSES BE RESTRICTED?

Unlike Equine Influenza which is transmitted between horses quickly, there’s a slower transmission time for EHV. Also, horses may not immediately show signs of the disease. It’s necessary to test horses for EHV at intervals of several weeks to ensure that all affected horses and any in-contact horses have tested negative before any movement can resume.

PREVENTION

If a horse is returning home from a part of the

ABOVE: A BLOOD TEST MAY BE NEEDED TO CONFIRM EHV AS THE CLINICAL SIGNS ARE SIMILAR TO OTHER CONDITIONS.

world where an outbreak has occurred, strict hygiene measures and biosecurity should be carried out. Isolate, make sure that horses don’t share equipment, and ensure anyone working with the horses washes their hands and uses a foot bath between each individual. Take each horse’s temperature twice daily, and keep a log.

Clean and disinfect all equipment and vehicles used to transport the horse.

Seek veterinary attention immediately if disease is suspected and stop all movements on and off the premises for at least 28 days in case of infection.

A vaccine against EHV-1 and EHV-4 is available but does not protect the horse against the neurological form. However, it can help reduce nasal shedding of the virus, its transmission to other horses and the severity of the respiratory form. Vaccination of horses known or suspected to have recently been in contact with EHV-1 is not recommended. Your vet will advise further on use of the vaccine.

Avoiding mixing in at-risk populations, close monitoring, early diagnosis and isolation of suspect horses remain the cornerstone of prevention regardless of vaccination status. 

These can vary depending on the strain.

Horses with EHV-1 can develop respiratory disease in the form of fever, coughing and nasal discharge. Some horses may develop neurological signs leading to incoordination of the hind (and occasionally fore) limbs, weakness, difficulty in urinating, bladder weakness and being unable to stand. These signs may be preceded by fever and respiratory signs.

EHV-4 infections commonly result in horses developing a fever, cough and clear nasal discharge. It can also cause abortion in pregnant mares, but this is less commonly seen.

TREATMENT

Horses showing early signs must be isolated and examined by a vet. Clinical signs are often seen within 10 days. Clinical signs may be similar to other diseases, so your vet will take nasopharyngeal swabs and blood samples to confirm the diagnosis.

Horses with the respiratory form of the disease may benefit from medication to reduce temperature and coughing, and occasionally antibiotics may be given to combat secondary bacterial infections. Euthanasia is usually required for horses who do not respond to support in slings.

The neurological form can be very difficult to treat successfully, but supportive care including anti-inflammatories, intravenous fluids and possibly support in a sling may be used. Euthanasia is usually required for horses who do not respond to support in slings.