Help Stop the Spread of EHV
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
CDFA: Recommended Caution for California Equine Events + All Non-Essential Horse Movements Postponed for at Least 14 Days
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.
