Equine Herpes

What is equine herpes virus?¹

Equine herpes viruses are a group of viruses which can cause contagious disease in horses.

The two most significant types are: Equine Herpes Virus 1 (EHV-1) and Equine Herpes Virus 4 (EHV-4) and they are often collectively referred to as Equine Herpes Virus (EHV).

It is reported that 80-90% of horses are infected with EHV before the age of 2 years old.

EHV can cause 3 types of syndromes:

HOW IS EHV TRANSMITTED?^1,2

Herpes viruses have the typical characteristic of staying dormant (latent) in the body after infection, just like cold sores in humans. Once a horse is infected with EHV it can remain present for life. Therefore, almost all horses are life long carriers of EHV.

Life long carriers

Carrier horses show no clinical signs, but the infection remains in their body. The virus can be re-activated at any time and spread to other horses.

Re-activation often occurs as a result of stressful conditions or a period of fatigue, for example:

During transport
Strenuous exercise
Mixing at equine events

This characteristic of herpes viruses makes it very difficult to combat EHV and explains why outbreaks can occur.

EHV can be transmitted by

Direct horse-to-horse contact
Nasal or ocular discharge
Infected equipment or by aerosol over short distances (e.g. adjacent stables)
Aborted foetus, foetal membranes or reproductive tract secretions
People who have been in contact with infected horses

Direct horse-to-horse contact
Nasal or ocular discharge
Infected equipment or by aerosol over short distances (e.g. adjacent stables)
Aborted foetus, foetal membranes or reproductive tract secretions
People who have been in contact with infected horses

Direct horse-to-horse contact

Nasal or ocular discharge

Infected equipment or by aerosol over short distances (e.g. adjacent stables)

Aborted foetus, foetal membranes or reproductive tract secretions

People who have been in contact with infected horses

what are the symptoms?

Variable and often unnoticed

The clinical symptoms of an EHV infection are very variable.^1,3

Young horses often show very pronounced flu-like symptoms, but EHV infection in an adult horse may go unnoticed.^1,3

As with many viral infections, an increase in body temperature over 38.5°C is often the first cause for concern.³

disease Symptoms

RESPIRATORY PROBLEMS

Signs of EHV respiratory disease are very similar to flu.³

Nasal discharge (clear to yellowish)
Coughing (sporadically)
A reduced appetite
Filling of the limbs
Signs of fatigue
Possible reduction in performance

ABORTION⁴

EHV is the most common infectious cause of foal abortions in mares.

Usually the mare shows no symptoms prior to abortion which occurs suddenly, most commonly in the third trimester of pregnancy.

Infection with EHV may have occurred recently or several months before abortion!

Neurological Disease²

EHV can cause a severe disease of the nervous system which is usually fatal.

Symptoms displayed are:

Ataxia (shaky walking)
Varying degrees of paralysis, especially in the hindlegs.
Onset of symptoms can be very sudden, without obvious prior respiratory problems, and usually occurs in the second week after infection.

how can i protect my horse?

Good yard management, particularly when dealing with potentially infected horses, is key to the control of the disease. Reducing the potential stresses that set off disease spread is important, as well as reducing issues such as overcrowding. Horses that are sick must be isolated.²

Vaccination against EHV is a central recommendation of the disease control strategy.⁵ Vaccinating your horse can help reduce respiratory disease and abortion. It will also help to reduce the amount of infective virus that is shed to other in-contact horses which may reduce the risk of outbreaks.^2,4

The best approach is to discuss EHV with your vet and within your yard - a group approach is the best way to manage the threat of this common disease.¹

Vaccination is particularly recommended for:⁴

Horses less than 5 years of age
Breeding studs or in areas with pregnant mares
Horses in facilities with frequent equine movement, including livery yards
Horses in venues where equestrian sports and disciplines take place

Speak to your vet to reduce the SPREAD of equine herpes virus1&4

EHV - What you need to know by Dr Richard Newton

References:

1. Allen GP. Respiratory Infections by Equine Herpesvirus Types 1 and 4. International Veterinary Information Service. 2002

2. Lunn, D. P., Davis-Poynter, N., Flaminio, M. F., Horohov, D. W., Osterrieder, K., Pusterla, N., & Townsend, H. G. Equine herpesvirus-1 consensus statement. Journal Of Veterinary Internal Medicine / American College Of Veterinary Internal Medicine, 23(3). 450-461, 2009. doi:10.1111/j.1939-1676.2009.0304.

3. Davis E. Disorders of the respiratory system. In: Reed SM, Bayly WM, Sellon DC, eds. Equine Internal Medicine, 4th ed. St Louis, MO: Elsevier; 2018:313-386

4. Equine Herpesvirus 1&4 Related Diseases. American Association of Equine Practitioners. 2017. Accessed April 10th 2019 from: https://aaep.org/sites/default/files/Guidelines/Equine%20Herpesvirus.pdf

5. Ivens P, Rendle D, Kydd J, Crabtree J, Moore S, Neal H, Knapp S, Bryant N, Newton JR. Equine Herpesviruses: A Roundtable Discussion. UK Vet Equine, July/Aug. 2019. Accessed June 2019 from: https://www.magonlinelibrary.com/page/ukve/resources

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