EHV-1

The International Equestrian Federation (FEI) cancelled international events in 10 countries in mainland Europe following the outbreak of an aggressive strain of the neurological form of Equine Herpes Virus, EHV-1, in at least four countries. Sadly, nine horses have died in this outbreak which is feared to be the worst in decades.

What is EHV 1?

EHV stands for Equine Herpes Virus This is a family of viruses which are named by numbers such as EHV 1, 2, 3, 4, 5 etc.  Currently there are nine different strains in this family but EHV 1, 3, and 4 pose the most serious health risks for domestic horses.

Equine Herpes Viruses are DNA viruses that are found in most horses all over the world. Almost all horses have been infected with the viruses and have most of the time, no serious side effects. It is currently unknown what causes some infected horses to develop the serious neurological forms associated with EHV1 that may be fatal.

What are some of the signs of EHV-1?

After infection, the incubation period may be as short as 24 hours, is typically 4-6 days, but can be longer. So, signs you may expect to see symptoms within a day of infection.

There are three forms of this disease in horses: respiratory disease, neurological form and abortion or neonatal death.

With a respiratory infection the signs include:

• A high fever that strikes in two phases: typically, the first causing a fever that peaks on day 1 or 2 and again on day 6 or 7
• Lethargy
• An initially clear nasal discharge that turns purulent
• Lymph node (under the jaw) enlargement and swelling in the throat lash area.

The neurological form is quite rare and typically there are minimal respiratory signs. The disease appears suddenly and usually progresses rapidly, reaching its peak intensity within 24 to 48 hours from onset of initial neurologic signs. Clinical signs of the neurologic disease may include:

• Ataxia - incoordination
• Hind limb weakness, progressing to front limbs
• Loss of tail tone
• Lethargy
• Urine dribbling
• Head tilt
• Leaning against a fence or wall to maintain balance
• Inability to rise.

How is it diagnosed?

Early detection is essential in limiting the spread of this highly infectious disease. PCR testing of nasal swabs and/or whole blood samples can provide quick results to confirm the diagnosis. It is important to know as early as possible and testing is a valuable tool in early detection.

PCR stands for “Polymerase Chain Reaction” test. This is a diagnostic test that analyses a sample to see if it contains genetic material from a virus.

What treatment exists for EHV-1?

There are two vaccination schemes:

• The first protects against the respiratory/poor performance form
• The second protects mares against the abortion or neonatal death.

This vaccination scheme does give protection against the respiratory form, but it is currently unconfirmed if it will provide protection against the neurological form.

How does EHV-1 spread?

EHV-1 is spread by direct horse-to-horse contact via the respiratory tract through nasal secretions.

However the virus can also be spread indirectly through contact with physical objects that are contaminated with it, such as:

• Human hands or clothing
• Equipment and tack
• Vehicles used for transporting horses
• Grooming equipment
• Feed and water buckets.

The air around the horse that is shedding the virus can also be contaminated with the infectious virus but it is difficult to establish the distance it can spread.

How long can the virus live outside of the horse’s body? 

The virus can survive up to 7 days in the environment under normal circumstances but can remain alive for a maximum of one month under perfect environmental conditions.

The most important measure is to first clean equipment and horse’s surrounding areas. Washing and rinsing surfaces when possible prior to applying disinfectants is recommended. Cleaning first allows for removal or organic material which makes the disinfectants more effective. After cleaning the surface, follow with a disinfection process. The virus is easily killed in the environment by most disinfectants. Conventional disinfectants and detergents are the best.

It is also important to wash your hands with soap and dry thoroughly or use an alcohol-based hand sanitizer when moving between horses to avoid spreading pathogens that may contaminate your hands.

How quickly do horses recover?

Recovery rates depend on the severity of signs and whether the horse has suffered secondary infections.

As long as there are no complications, horses with the respiratory form should usually make a good recovery within a few weeks.

The neurological form is understandably of greater concern. Severe cases can be fatal. For less severe cases, recovery is likely to take several months.