EHV-1

10 Things You Might Not Know About Equine Herpesvirus-1 (EHV) and Equine Herpes Myeloencephalopathy (EHM) - UC Davis Center for Equine Health

UC Davis Center for Equine Health
by Amy Young, March 04, 2022

  • EHV-1 is a common virus in the horse population. Horses are typically exposed to EHV-1 early in life, with 80-90% of horses reportedly infected by two years of age. The virus may not make the horse sick at the time, but it can enter a period of latency and become reactivated later in response to stress or other factors. Subclinical carriers can shed the infectious organism into the environment, presenting potential sources of infection for other horses. It is important to note that the bulk of the disease is rhinopneumonitis, a respiratory infection. Abortions and neurologic cases are rare.

  1. The incubation period of EHV-1 infection is highly variable. The time from infection to observable clinical signs (incubation period) depends on the individual animal, the virulence (severity) of the virus, and environmental factors such as stress. The average incubation period is 4 to 7 days, with some taking up to 14 days. When neurological disease occurs, it is typically 8 to 12 days after the primary infection involving fever.

  2. EHV-1 is commonly diagnosed from nasal swabs or blood samples. Polymerase chain reaction (PCR) is used to amplify the DNA of the virus so that it can be detected. In California, the neurologic form, EHM, is a reportable disease and therefore the California Animal Health and Food Safety Laboratory (CAHFS) must perform EHV-1 testing in suspected cases. Positive cases tested at a non-state diagnostic laboratory need to be confirmed by CAHFS. The laboratory recommends submitting both a nasal swab sample and a blood sample if possible.

  3. There are three different primary genotypes of EHV-1: neuropathogenic, non-neuropathogenic and a new variant. The neuropathogenic genotype is designated as EHV-1:D-752. The non-neuropathic genotype is EHV-1:N-752 and the new variant is EHV-1:H-752. All three genotypes have been associated with neurologic signs. These three genotypes are genetically distinct, enabling testing to perform EHV-1 subtyping on nasal swabs and blood samples.

  4. Random EHV-1 testing of horses outside of quarantine areas or in unexposed stables is not currently recommended. The detection of virus through PCR analysis does not provide a diagnosis in the absence of clinical signs and/or other corroborating information because low levels of non-replicating virus may be the source of the viral DNA detected. The relationship between individuals who test positive but never develop clinical signs and those that test positive and actually develop clinically significant disease is unknown. Research in this area is ongoing.

  5. Fever is the most consistent initial clinical sign of EHV-1 infection. Elevated temperatures (≥101.5 °F in horses not receiving any anti-inflammatory drugs) that otherwise appear healthy can be early indicators of EHV-1 (and other) infections. Treating horses in the early stages of infection, or even before other clinical signs appear, often results in better outcomes and can significantly limit the spread of disease. Take and record horses’ temperatures regularly and talk to your veterinarian if you notice elevated temperatures in otherwise healthy horses. Enforce proper biosecurity measures to keep your horse healthy at home and away from home. Some microchips have temperature sensors (thermochips) and pair with a smartphone app to simplify regular body temperature monitoring.

  6. There is no vaccine for EHM. Vaccines are available that are licensed for protection against the respiratory disease and abortion related forms of EHV. None of these vaccines prevents the neurologic form of EHV-1. However, they may decrease nasal shedding of EHV-1, thereby limiting the spread of infection and outbreaks. The most up-to-date guidelines on these vaccines is available through the American Association of Equine Practitioners (AAEP). The intent of vaccination requirements for licensed competitions is to promote proper vaccination protocols in accordance with AAEP recommendations.

  7. The EHV-1 virus can travel through the air, but can only spread for a maximum distance of 30 feet. It is primarily spread directly through horse-to-horse contact and indirectly on contaminated objects (fomites) such as hands, clothing, tack, buckets, etc. (where it can remain viable for four to six hours). Infected horses primarily shed the virus in nasal secretions.

  8. EHV-1 can survive in the environment for 7 - 30 days, but it is susceptible to disinfectants. Bleach and alcohol disinfectants are effective against EHV-1. However, it is important to remember that these types of disinfectants are inactivated by organic matter (soil, manure, etc.). Therefore, it is important to use soaps or detergents to remove any organic matter prior to applying a disinfectant. It is also important to follow manufacturer’s instructions as specific contact times are needed to inactivate disease organisms and vary by product. Accelerated hydrogen peroxide products, such as Accel/Rescue® and Intervention™, hold up better to organic matter and have a comparatively short contact time.

  9. Treatment of EHM usually focuses on reducing inflammation. A combination of anti-inflammatories such as flunixin meglumine and prednisolone, free-radical scavengers such as dimethyl sulphoxide and vitamin E, and even aspirin have been used to treat clinical signs. Antivirals such as valacyclovir have been utilized to decrease viral load and prevent severe neurologic signs. However, to date, controlled studies to evaluate the efficacy of various approaches to EHM prevention are lacking. Additional supportive treatments can be implemented on a case-by-case basis.

LEAN MORE: https://ceh.vetmed.ucdavis.edu

California EHV-1 Update as of March 3, 2022 and Suspension of USEF Competitions in California for 14 Days

From the US Equestrian Communications Department

Lexington, Ky. - USEF continues to work closely with the California Department of Food and Agriculture (CDFA), competition organizers, and participants to manage the EHV-1 situation in CA and provide updates to our membership. The information provided below is based on information available to USEF at the time of distribution.

In an effort to mitigate the risk of further spread of EHV-1, all USEF Licensed competitions in CA are suspended for the next 14 days. In line with the CDFA release today, USEF does not have any hunter/jumper competitions taking place for the next 28 days. We appreciate the collaboration of organizers to cancel events to support this effort. 


As the return to competition protocols are implemented, more horses will be tested which will result in more positive test results for horses. EHV-1 lives dormant in many horses. The increase in positives is expected as we test asymptomatic horses for EHV-1. The additional testing will allow the USEF community to mitigate the spread of the virus and safeguard horses. Dr. Nicola Pusterla, Professor Medicine and Epidemiology, UC Davis Veterinary Medicine explained, “We all recognize that horses with clinical EHV-1 disease (fever, nasal discharge and even neurological signs) are high risk when it comes to risk of transmission. What most people forget is that infection does not always translate into disease, meaning that adult horses can shed EHV-1 without displaying any abnormal clinical signs.” The expected increase in confirmed positive EHV-1 cases is not necessarily alarming if the horse is asymptomatic.
 
As a further measure to protect horses and facilitate tracking, USEF will be providing an EHV-1 Declaration Form to competitions for competitors to complete when they arrive on competition grounds.

 

USEF will also make available an EHV-1 Test Result Form to be submitted to EHV@usef.org along with evidence of negative test results. These documents will be required under the return to competition protocol in order to get a horse’s ineligibility status lifted. This return to competition protocol applies to any horse that has been on the DIHP or Rancho Murieta Showgrounds, or any horse that has been exposed to a horse confirmed positive for EHV-1 off competition grounds in the past 14 days. This will allow the horse to be released from the EHV-1 Ineligibility List.

FEI Return to Competition Protocols

In order for a horse to return to FEI competition, the following requirements must be met:

FEI horses MUST have a negative EHV-1 PCR test to return to competition

• Two negative PCR tests within 14 days, one at Day 7 and one at Day 14
   OR

• One negative PCR test within 21 days, at Day 21

USEF Return to (National) Competition Protocols

In order for a horse to return to USEF (National) competition, the following requirements must be met:

•Two negative PCR tests within 14 days, one at Day 7 and one at Day 14
OR•One negative PCR test within 21 days, at Day 21
OR•28 days without a test, if the horse has been isolated for a minimum of 28 days

It is critical that everyone follow biosecurity protocols in order for this situation to improve. Please note that the USEF protocols for testing to return to competition may be more extensive than those of the CDFA.


If you have questions on the USEF protocols, please email USEF at EHVhelp@usef.org. For additional information, please refer to the California Department of Food and Agriculture and Equine Disease Communication Center websites.

FAQ: USEF Return to Competition Protocols and California Hunter/Jumper Calendar in March

FAQ: USEF Return to Competition Protocols and California Hunter/Jumper Calendar in March

From the US Equestrian Communications Department

1.What is required for my horse to return to USEF competition if it participated at Thermal or Rancho Murieta?
USEF requires either one of the following to clear your horse for eligibility to compete:•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 left the venue at Thermal or Rancho Murieta, whichever occurred later. Both swabs must result in negative test results to EHV-1.

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 fulfil USEF requirements.
OR•The horse must be isolated for 21 days, rectal temperature must be taken and recorded during the isolation period, and samples must 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 left the venue.

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 a further seven days and be re-tested.
2.Are these restrictions applicable to horses returning to their home barns?
No, the criterion for testing only applies to those horses entering USEF competitions. However, it is always a good practice to isolate, as much as possible, those horses returning to their resident barn after attending a competition.
3.Do I need to test my horse if I isolate the horse at home for more than 28 days, do I need a test?
No, but you may be required to show a twice daily temperature log for the last 14 days of the isolation period. In light of the fact there are no currently scheduled Hunter/Jumper competitions to be held in the state of California until March 30, the 28-day approach may the best option for many, and would eliminate testing asymptomatic horses.
4.Where do I send evidence of negative test results?
Test results must be submitted via email to EHV@usef.org to obtain clearance to compete.
5.Did USEF cancel all upcoming California competitions?
USEF has not canceled any upcoming CA competitions. Competition Managers voluntarily canceled all CA USEF hunter/jumper competitions that would have occurred before March 30. Currently, hunter/jumper competitions in CA will resume on March 30.
6.Why are only hunter/jumper competitions shut down in California?
At this time, we are not aware of any confirmed positive associated with non-hunter/jumper horses.
7.If the EHV-1 infection rate begins to decrease, will USEF approve new competitions to the CA hunter/jumper calendar for March?
No, USEF will not approve any new competitions to the CA hunter/jumper calendar that would occur before April 1.
8.How will cancellations affect qualifying criteria and selection procedures?
Each Discipline is reviewing the impact on Selection and Qualification and further announcements will follow.
9.Do I have to take my horse to a different location before going to a USEF competition, after isolating at one of the venues that have had confirmed positive(s) for EHV-1; i.e. Desert International Horse Park (DIHP) or Rancho Murieta?
No so long as the horse isolated for 21-days at the venue and obtained a negative PCR test. Day 0 will be the date of the last fever that is associated with a confirmed positive EHV-1case at the venue. New confirmed positive cases will reset Day 0.
10.Why is this affecting vaccinated horses?
Similar to COVID-19 in humans, vaccinations do not provide 100% protection from the virus. EHV-1 vaccines have been shown to decrease nasal shedding of the virus, and, in some cases, to reduce the amount of virus present in the blood. Vaccination for EHV-1 can also lessen the clinical presentation in horses and shorten the duration of disease. The virus is endemic and cannot be eradicated, it can only be controlled. Horses have been exposed to the virus before they are ever vaccinated.
11.Should non-competing horses (training or sale horses) be taken to a horse show?
It is USEF’s recommendation that any horse that is not competing should not be on competition grounds at this time. This makes it easier for the tracking of on-site horses, if necessary, and reduces the number of horses that are potentially exposed or might be carrying the active virus.
12.Do I need to show evidence of my horse’s vaccination status at USEF competitions?
All competitions are encouraged to check vaccination status of all horses coming onto their competition grounds and to verify they are compliant with GR844. You must have evidence of compliance upon request.
13.What is the difference between the reportable disease classifications of “Reportable and Monitored” and “Reportable and Actionable”?
Individual states consider a variety of equine diseases as ‘reportable’ but they do not take action on it. California considers a case of Equine Herpes Myeloencephalopathy (EHM) as a “Reportable and Actionable” disease in equids. This means that the CDFA will manage a quarantine. They do not manage quarantines for EHV-1 cases unrelated to EHM.
14.How can I isolate horses at home when I don’t have separate facilities?
Talk to your veterinarian and consult the CDFA recommendations and resources available at EDCC.
15.How can I mitigate the risk of my horse contracting EHV-1?
This is a calculated risk any time a horse is traveling to a high-density population; this is a disease of control, it cannot be eradicated. We encourage you to carefully review with you veterinarian healthcare measures to safeguard you horse, as well as biosecurity resources that can found at the CDFA and EDCC websites.

California EHV-1 Update, February 26, 2022

February 26, 2022

California EHV-1 Update, February 26, 2022

Lexington, Ky. - USEF continues to work closely with the California Department of Food and Agriculture (CDFA), competition organizers, and participants to manage the EHV-1 situation in CA and provide updates to our membership. The information provided below is based on information available to USEF at the time of distribution.


USEF learned last night about three (3) new horses confirmed positive for EHV-1 with no neurologic signs. One horse is at DIHP in isolation. The other two horses are off site. One horse had returned to its home premises in Riverside County and is isolated. The other horse left DIHP 14 days ago and confirmed positive for EHV-1 while at a competition in Rancho Murieta. The horse has left the competition and has been isolated and quarantined at its home premises. 


We are pleased to report that we also learned that two of the first three horses confirmed positive for EHV-1 at DIHP are doing well clinically and have been cleared to leave isolation.


It is critical that everyone follow biosecurity protocols in order for this situation to improve. Please note that the USEF protocols for testing to returning to competition may be more extensive than those of the CDFA.


If you have questions on the USEF protocols, please email USEF at EHVhelp@usef.org. For additional information, please refer to the California Department of Food and Agriculture and Equine Disease Communication Center websites.