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Recently, cases of Equine Herpesvirus were reported in Riverside. Below is a transcript about the virus from UC Davis, please read and familiarize yourself with this important information:

Equine Herpesvirus-1 Alert
Information about Equine Herpesvirus-1 (EHV-1)

What is Equine Herpesvirus-1?

Equine herpesvirus 1 (EHV-1) is one of a large group of DNA viruses causing potentially serious disease in horses and other species. EHV-1 has two forms—one that causes abortion in mares and one that causes respiratory infection and neurological symptoms. The most recent outbreaks of concern have involved the EHV-1 respiratory/neurological form of the virus.

EHV-1 is contagious and is spread by direct horse-to-horse contact, by contaminated hands, equipment and tack, and, for a short time, through aerosolization of the virus within the environment of the stall and stable.

What are the Clinical Signs of EHV-1?

The initial clinical signs of the infection may be nonspecific and include fever of 102ºF or greater. Fever may be the only abnormality observed. Other presenting signs may be combinations of fever and respiratory symptoms of nasal discharge and cough. Some horses have reddish mucous membranes.

Horses with the neurological form of EHV-1 can soon become uncoordinated and weak and have trouble standing. Difficulty urinating and defecating may also occur. Often the rear limbs are more severely affected than the front.

Signs of brain dysfunction may occur as well, including extreme lethargy and a coma-like state. The incubation period for the infection is 2 to 8 days. Once a fever occurs, clinical signs can progress to nervous system involvement over the next 1 to 7 days.

Vaccinations

While there are several vaccines available for protection against both respiratory and abortogenic forms of EHV-1, at this time there is no equine vaccine that has a label claim for protection against the neurological strain of the virus. Consult your veterinarian for further guidance if you are considering the use of EHV-1 vaccines.

How to Handle a Sick Horse

Isolation of sick horses and early determination of the cause of their symptoms is very important. It is prudent to determine if the horse has been around horses that may have been in a place where EHV-1 has been documented to occur. Infections other than EHV-1 can also spread by horse-to-horse contact, so keeping a horse with a fever isolated is a very good practice in any case.

If your horse develops fever, respiratory signs or neurological signs, immediately notify your veterinarian and do not move the horse or horses in the immediate area. Alert those who have horses in the adjacent area to cease all movement of horses in and out of the facility until a diagnosis is confirmed by testing. If horses are exposed and then travel to a new stable or show, the infection can spread to other horses at that new location.

EHV-1 does not persist in the environment for a long time, but disinfection of premises, stalls, trailers and so forth is indicated. If you handle a horse with EHV-1 and don’t wash hands or change clothing, you may spread the infection to other horses. A solution of 1 part chlorine bleach to 10 parts water is effective for decontaminating equipment and environment.

Control Measures

Suggested Approach for Control of Potential Outbreaks of EHV-1 as of January 12, 2007

Horses exhibiting sudden and severe neurological symptoms consistent with a diagnosis of EHV-1 pose a definite risk to the surrounding population of horses. Consequently, early intervention to prevent the spread of infection is required. Disease control measures based on established medical practices and recent successful experiences to control the spread of EHV-1 indicate the following measures to be reasonable.

Isolation of Sick Horses

To prevent an infected horse from having any further contact with other horses in the stable environment, any individual horse with clinical signs consistent with neurological EHV-1 infection should be removed immediately from the area of other horses and placed in a separate enclosure designated for infectious disease isolation. This isolation stall or enclosure should be located well away from high traffic areas associated with other barns or training areas. Animal caregivers should take precautionary measures to ensure that they do not transmit disease to other horses through contaminated hands, clothing, equipment or tack. It is essential that the isolation facility have supervised oversight by an individual knowledgeable in disease control and quarantine procedures to avoid the possibility of contamination.

Segregation of Exposed Horses

Horses known to have had intimate contact with the diagnosed clinical case of EHV-1 should be maintained in their existing barns and segregated from other horses during exercise periods until the sick horse has been confirmed to have EHV-1 by PCR testing.

Quarantine Procedures

Once the confirmation of EHV-1 is made, appropriate focal quarantine measures to restrict the movement of all potentially exposed horses will be necessary to prevent the possible spread of disease to other locations. These procedures may begin with initial restrictions such as the quarantine of those individuals in the immediate area of exposure (i.e., a single barn or other unit of housing) within a horse facility. Horses in the immediate contact area of the clinically affected individual should be tested for EHV-1, as should any other horse that exhibits fever or other clinical signs consistent with EHV-1 infection. Since stress may play a role in eliciting the onset of clinical signs, horses stabled in areas of known exposure should not be subjected to strenuous physical exercise or long-distance transport until their health status can be determined.

Expanding the Quarantine Area

If new clinically ill or EHV-1 positive horse(s) are identified in other locations within the equine facility, an additional focal quarantine of exposed horses should be instituted at that location. The area under quarantine may be expanded to include other affected barns. If multiple cases are identified or suspected, the entire stable area may need to be quarantined. The optimum strategy should be the prudent imposition of a series of focal quarantine procedures using an expanding series of “concentric rings” of disease control.

Individual animals that have tested positive for EHV-1 within the designated quarantine area, whether symptomatic or not, should be retested periodically until disease is confirmed or eliminated based upon both a negative PCR test and a lack of clinical signs for the disease. Quarantine measures should be maintained until an absence of further clinical cases and positive tests suggest no new appearance of disease is occurring. At that time, a gradual drawdown of these procedures can be applied. Areas of the facility under focal quarantine may have their restrictions rescinded in a reverse of the concentric-ring approach.

Horses Outside the Quarantine Areas

Since the positive predictive value* of PCR-based tests for EHV-1 in asymptomatic horses is uncertain at this time, horses outside of quarantine areas or in unexposed stables should not be tested on a random basis. The finding of a positive PCR test result in an asymptomatic horse does not provide conclusive evidence of either active infection or the potential for disease transmission, because low levels of nonreplicating virus may be the source of the viral DNA detected. This means that the detection of virus through PCR analysis does not provide a diagnosis in the absence of clinical signs and/or of other corroborating information. Therefore, the use of this technology as a screening tool for EHV-1 in clinically normal, nonexposed horses is considered inappropriate.

* The positive predictive value of any medical diagnostic test is the relationship between those individuals who test positive to the number of those testing positive that actually develop clinically significant disease.

Diagnostic Testing

Your veterinarian can perform a nasal swab and blood collection and send it to a laboratory where an assay (real-time TaqMan® polymerase chain reaction, PCR) for neurological EHV-1 virus can be performed. Use of other tests may not be as reliable, based on the most recent scientific publications.

UC Davis has two laboratories that are capable of performing diagnostic tests:

California Animal Health and Food Safety Laboratory
Submission forms and shipping requirements
www.cahfs.ucdavis.edu/
(click on "Standard Submission Form")

Lucy Whittier Molecular and Diagnostic Core Laboratory
Submission forms and information
www.vetmed.ucdavis.edu/vme/taqmanservice/diag_home.html
(click on "Submission Forms" in left column)

Samples for EHV-1 testing should consist of nasal swabs and whole blood samples drawn in EDTA tubes.

The Gluck Equine Research Center in Lexington, Kentucky, is the OIE reference laboratory for EHV-1. Further information regarding EHV-1 can be obtained at www.ca.uky.edu/gluck/BiblioEHV1.asp.

Cautionary Note Regarding Diagnostic Testing
The California Animal Health and Food Safety Laboratory (CAHFS) offers two real-time PCR assays (qPCR) for the detection and differentiation of neuropatholgenic Equine Herpesvirus-1 from non-neuropathogenic EHV-1. The assays developed by Dr. George Allen at the Gluck Equine Research Center, University of Kentucky, detect viral DNA and distinguish between the two strains by identifying the genetic difference located in the polymerase gene. Dr. Allen’s work is described in Equine Veterinary Journal 3:252-257 (2006).

While these real-time PCR results indicate the presence or absence of viral DNA in the specimen tested, they do not predict clinical outcome. Dr. Allen’s work with experimentally infected foals suggests a five-fold higher risk of a horse developing neurological disease when infected with the form of EHV-1 containing the neuropathogenic marker. The real-time PCR testing can be performed on nasal-pharyngeal swabs, EDTA blood (buffy coat), or postmortem tissues. CAHFS will routinely perform both assays for all samples submitted for EHV-1 detection.

The Lucy Whittier Molecular and Diagnostic Core Laboratory also offers routine diagnostic testing for equine viral pathogens using real-time PCR technology.

The Whittier Laboratory offers a well-validated assay, which detects all strains of EHV-1 by targeting the glycoprotein ß gene. This assay detects the EHV-1 virus but does not differentiate between the various neurogenic strains or the EHV-1 abortion strain, which is considered to be less risk for neurological disease. The sub-differentiation of various strains will be possible in the near future, but until then the molecular detection of EHV-1 by real time PCR should be correlated with clinical presentation (abortion, pneumonia, myeloencephalopathy). For example, a neurological horse with fever and positive PCR has a strain of EHV-1 and should be treated as contagious with all handling guidelines followed.

The PCR assay is performed on either whole blood or nasal secretions in order to document viremia and nasal shedding, respectively.

Research groups have recently identified a region of variation in the genome of different EHV-1 strains that correlates directly with their ability to cause a more virulent form of neurologic disease. Current estimates for the neurogenic strains isolated from exposed horses that have this mutation range from 70 to 94%. In addition, the nonmutant strains of EHV-1 also have historically been implicated as a causative agent for neurological disease.

Currently, molecular assays to differentiate between neurogenic and non-neurogenic strains have been developed and used for research purposes only. While these assays are informative, we believe it is too early to use these types of assays in the diagnostic setting without additional validation. The assay we offer for all strains of EHV-1 will be our standard at this time.

Appropriate use of PCR Testing for EHV-1

Since EHV-1 is considered to be endemic within the horse population, random testing of normal horses for EHV-1 by PCR diagnostics can and likely will detect horses with nonreplicating (dead) viral DNA; latent, low-level, transient carriage of virus; or viral levels that are not sufficient to pose a significant risk for disease transmission. Until more research data regarding the pathogenesis and epidemiology of equine herpesvirus-1 myeloencephalopathy (EHM) is acquired, random testing of horses for the virus may very well result in interference with the free movement of horses and staging of their athletic competitions, which later may be demonstrated to have been unnecessary.

It must be understood that the positive predictive value of any medical diagnostic test is the relationship between those individuals who test positive to the number of those testing positive that actually develop clinically significant disease. Only if that relationship is very close does the diagnostic test have a high positive predictive value.

For example, with equine infectious anemia (EIA), the number of horses testing positive (Coggins test) matches very closely with those that are actively infected and so have clinical significance for transmission of disease. Thus, the Coggins test has a high positive predictive value. By contrast, with equine protozoal myeloencephalitis (EPM), there is a marked difference between the numbers of horses testing positive in the Western Blot test and those who actually exhibit symptoms of the disease. Consequently, it is well accepted that the Western Blot test has a low positive predictive value for EPM.

With our current outbreaks of EHV-1, the interpretation of the positive predictive value of the diagnostic technology employed and the “test result” obtained are problematic at this time. Even given the sophistication of our current molecular testing capabilities, the interpretation of PCR viral detection for EHV-1 should be done only in the context of the presenting clinical signs for disease in the horse being tested.

At this time the significance of a positive PCR in an asymptomatic horse is unknown, regardless of the test being employed or the laboratory performing the test. There is simply not sufficient information yet acquired to justify or recommend control measures or quarantine procedures for horses testing positive for EHV-1 in the absence of clinical signs of disease, unless they have had intimate contact with a known clinical case.

Horses with high fevers and/or clinical signs of coughing or mild nasal discharge, with or without neurologic symptoms, should be tested for EHV-1 by PCR diagnostics if other explanations for these signs of disease are not apparent. Detecting a positive PCR for EHV-1 in these circumstances may warrant some degree of patient isolation and limited movement of exposed horses.