Equid herpesvirus 1 (EHV-1)

Herpesviruses are found in most horses all over the world. Equid herpesvirus 1 (EHV-1) is a DNA virus that belongs to the most common and most important herpesviruses in horse population. They cause respiratory and neurological diseases and abortion in pregnant mares.

The most common signs of this disease include fever, cough, nasal discharge, lethargy, weakness, loss of appetite, enlargement of lymph nodes or conjunctivitis up to ocular disease. Some infected horses may develop serious neurological disease. The most frequent signs are ataxia (incoordination, hind limb weakness), inability to rise, urine retention or incontinence. In new-born foals, EHV-1 causes hepatitis, pneumonia, respiratory distress, and death. In pregnant mares, abortions occur mainly in the last four months of pregnancy without any preceding warning sings.  The infected pregnant mares abort from 2 weeks to several months after initial infection.

The incubation period of this viral disease is typically 4 – 6 days, and the clinical signs occur 10 days after initial infection and can be easily overlooked (e.g., only fever). After the symptoms subside, the viral shedding will persist for at least one week.

After going through the primary infection, most horses become inapparent carriers of the virus. That means that the horses remain persistently infected for the whole life. These latent infected horses do not shed EHV-1 in nasal secretions and are not infectious to other horses. However, the virus may reactivate under suitable conditions (stress, immunosuppression, travelling, races, etc).

Virus is spread through exposure to virous-containing droplets in the air from horse to horse over the distance from 5 to 10 metres.  It can be also spread by contaminated clothing and outfit of persons working with horses or in boxes and transport trailers. Travelling with horses and events with presence of many horses such as races, exhibitions, shows, etc. in limited areas are at risk due to high concentration of horses.

The International Federation of Equestrian Sports (FEI) has taken measures that must be implemented by 12 April 2021 to ensure the safety of such events as regards the high health of the horses. It is necessary that strict hygienic conditions for stabling and transport of horses are met, veterinary checks performed, and other action taken (e.g., regular temperature measurement).

The participation in an event with more than 400 horses is subject to negative PCR-test for EHV-1 for horses stabled overnight or transported by plane. The test sample shall be taken by an authorized veterinarian to carry out the test. The test sample must be taken not earlier than 96 hours before arrival at the event. The laboratory report must contain ID of the horse and date and time of sample taking.

Events such as races, competitions, exhibitions, or other shows organised on the territory of the Czech Republic must meet the current conditions of participation in horse gatherings with high concentration of horses according to the State Veterinary Administration of the Czech Republic. This public administration body determined vaccination against EHV-1 or a negative PCR test as a precondition for organisation of the horse gathering at least till the end of 2021.

The PCR-test (Polymerase Chain Reaction) is a method that enables to detect the presence of a virus in DNA and find out whether the horse is infected. The test shall not be older than 10 days and the decisive day is the date of sample taking.