USEF, in conjunction with the California Department of Food and Agriculture (CDFA), has created the following FAQ with up-to-date information regarding the EHV-1 outbreak. 

The responses below are based on information available to USEF at the time of distribution. The situation in California is fluid. Updates will be provided as additional information becomes available.

1. What is Equine Herpes Virus?

Equine Herpes Virus-1 (EHV-1) is a virus that is present in the environment and found in most horses all over the world. Horses are typically exposed to the virus at a young age with no serious side effects.

2. Are there different strains of EHV-1?

There are two strains of EHV-1:

  • The wild-type (aka non-neuropathogenic) strain; and
  • The mutant-type (aka neuropathogenic) strain of EHV-1.

It is important to note that neurologic symptoms have been identified with both strains of the virus.

3. What is Equine Herpes Myeloencephalopathy (EHM)?

EHM is the neurological disease syndrome caused by the EHV-1. In this syndrome, the EHV-1 virus damages blood vessels in the brain and spinal cord causing the various neurologic clinical signs.

4. How does the disease spread?

EHV-1 is spread by direct horse-to-horse contact. The virus may also be spread indirectly through contact with objects contaminated with the virus, such as clothing, human hands, equipment, tack, trailers, feed, water buckets, and wash rags. The virus can become airborne but only for short distances.

5. How many horses have tested positive for EHV-1 that were on the grounds at DIHP or associated with horses that had been on the grounds of Desert International Horse Park (DIHP)?

To date, 18 horses have confirmed positive for EHV-1. Some of these horses tested positive after leaving DIHP.

6. How many horses have tested positive for EHM that were on the grounds at DIHP?

To date, three (3) horses from DIHP have confirmed positive for EHM (EHV-1 infection with neurological signs). One of these horses had to be euthanized.

7. Is there a relationship between DIHP and the euthanized horse that competed at Los Angeles Equestrian Center (LAEC)?

At this time, there is no known direct link between the DIHP and the euthanized horse confirmed positive for EHM (EHV-1 infection with neurological signs) that competed at LAEC.

8. Did horses leave DIHP and within 7 days compete at LAEC against LAEC’s protocols?

We have reports that four horses left DIHP and within seven days competed at LAEC against their protocols. Those horses were removed when this became known to management. USEF is investigating these reports.

9. Is there a relationship between DIHP and the euthanized horse in San Juan Capistrano?

The euthanized horse in San Juan Capistrano confirmed positive for EHM (EHV-1 infection with neurological signs) had not been to DIHP, but was exposed to other horses upon their return from DIHP. One of the returned horses confirmed positive for EHV-1.

10. Where can I find up-to-date information this?

Updates on confirmed cases are reported on the California Department of Food and Agriculture and Equine Disease Communication Center websites. Please do not rely on information from social media or word of mouth.

USEF Mandate on EHV-1 Restriction of Entries

In an effort to mitigate the risk of virus transmission, the USEF is requiring the following protocols, which are effective immediately and until further notice.

1. Isolate your horses

Horses that within the last 14 days were on the grounds at Desert International Horse Park (DIHP) or have been in-contact with these DIHP horses must be isolated.

2. Take rectal temperatures

Rectal temperatures of all of your horses should be taken and recorded twice daily. Horses that develop a fever should be examined by a veterinarian.

3. Laboratory testing for EHV-1

Horses that were on the grounds at DIHP must meet the following requirements:


Two samples taken using nasopharyngeal swabs must be analyzed by PCR testing on day 7 and day 14. Day 0 is considered to be the day your horse is in a new location. Both swabs must result in negative test results to EHV-1 in order to satisfy the requirements of the USEF. If either of the tests generate a positive result, the horse must remain in isolation and be re-tested. It is necessary to have two negative test results, taken at least seven days apart to fulfill USEF requirements.


The horse must be isolated for 21 days, rectal temperature must be taken and recorded during the isolation period. Samples to be taken after day 21 using a nasopharyngeal swab to test for EHV-1 via PCR analysis. Day 0 is considered to be the day your horse is in a new location. The swab must result in negative PCR test result to EHV-1. If the tests generate a positive result, the horse must remain in isolation for an additional seven days and be re-tested.

4. Release from Isolation

Horses must only be released from isolation on the advice of your veterinarian.

5. Return to Competition

Horses that have been on the grounds at DIHP within 14 days preceding a USEF competition are not permitted to enter any USEF competition ground until they have fulfilled the testing requirements described above. Test results must be submitted via email to to obtain clearance from this restriction.

6. Penalties

Noncompliance with these protocols will result in penalties imposed on trainers and owners as well as competitions that knowingly permit noncompliant horses on the grounds.