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Equine Herpes Virus



2014 Equine Herpes Virus Outbreak:
Update May 13, 2014

    We are hoping this will be the last necessary update regarding the EHV-1 outbreak. The outbreak began in March 2014 and involved the non-neuropathogenic strain of the Equine Herpes Virus mainly affecting barrel horses. Several states were involved including Iowa (1), Kansas (1), Minnesota (7), North (3) and South (1) Dakota, Nebraska and Wisconsin (4). There is not sufficient evidence to prove that all the cases from around the country are connected. Due to the early detection and quarantine of cases and barns along with the no travel recommendations this outbreak was contained to a 2 month period and we are hopeful that everyone will be able to have a fun summer and show season.

Update April 4, 2014:

     The total number of cases connected to this outbreak is currently at nine with horses from Minnesota, Wisonsin and Iowa being affected.

     One of the cases from Wisconsin from Burnett Co that was euthanized tested negative for EHV-1 on the post-mortem and has been removed from the list of cases. However, an additional case of suspected Equine Herpes Virus-1 has been reported  in St. Croix County. The horse is receiving treatment while tests are pending and, if positive, the total number of confirmed cases would be ten.

For further updates on cases from Wisconsin please follow this link to the Wisconsin Department of Agriculture.






The Minnesota Department of Animal Health has a map of the cases which can be downloaded here:





We also wanted to share the University of Minnesota presentation by Dr. Carrie Finno from March 26th, 2014.






Update March 31, 2014:

     There are now a total of nine confirmed cases of EHV-1 from counties in Minnesota, Wisconsin and most recently a horse in Iowa that had traveled to Minnesota. These cases have been reported as "non-neuropathogenic" EHV-1, though you have all been told that the outbreak involves the neurologic form of EHV-1. We see where the confusion is and will try to explain.


     There are 2 forms of EHV-1. The form that causes abortion in mares and the form that causes respiratory infection and neurologic symptoms. The second form can be broken down into the neuropathic strain and the non-neuropathic strain. The non-neuropathic is less viremic but can still produce neurologic disease. They both can cause EHM (Equine Herpesvirus Myeloencephalopathy) which is what causes the neurologic symptoms that have been seen.


     I really see no reason in differentiating between the two other than one may be more viremic and is considered "reportable". In my humble opinion they both should be considered reportable in the face of an outbreak because they are both very contagious and can cause neurologic disease with a high mortality.


     As far as getting your horse vaccinated this is the deal: It may be beneficial to vaccinate NON-exposed horses that have not been vaccinated for EHV-1 in the last 60 days. As you know the vaccine isn't labeled for the forms of EHV-1 that cause myeloencephalopathy but may theoretically help with the reduction in severity of clinical signs, and reduce shedding and viremia. We hope this helps with the confusion. Bottom line: if everyone goes nowhere with their horse/s, this goes away.

Update March 26, 2014:

    There has been a lot of information coming your way, from many different sources, regarding this outbreak. Our intent here is not to sound the alarms but to give you the information you need to make the best decisions for your horse/s. We will attempt to make this brief with the important points only.


     There is an Equine Herpes Virus (EHV-1) outbreak developing in the Twin Cities area. As of March 26, 2014 eight cases have been confirmed in horses from Chisago, Dakota, Freeborn, Hennepin and the latest in Wright County Minnesota as well as Polk and Burnett County Wisconsin. Of these cases, three have been euthanized. At this time we recommend no horse travel, especially to barrel racing events, to limit exposure until we have more information. We will keep you posted as we get more information.


     Equine Herpesvirus (EHV-1) neurologic strain is what the outbreak concern is and there are currently no equine vaccines labeled to protect against this strain. Protection from the respiratory form of this can be prevented by the "Rhino vaccine" your horse normally would receive. This vaccine does not protect against the neurologic form although may theoretically reduce nasal shedding and viremia. Rhino vaccines have a short effectiveness and may need to be boostered.



Highly contagious!

Horse-to-horse contact

Aerosol transmission (airborne)

Contaminated hands, equipment, tack, feed...

The virus can live for several weeks in the environment once it has been shed by a horse. (Up to 35 days)



As short as 24 hours Typically 4-6 days but can be longer



Horses can shed virus for 1-3 weeks past resolution of clinical signs.



Fever precedes other clinical signs

Respiratory disease - fever, cough, nasal discharge

Abortion in pregnant mares

Neurologic disease - Incoordination, usually hind end, urine retention/dribbling, recumbency.

*Neurologic signs may be preceded by fever and respiratory signs.*



Limit exposure, quarantine your barn from unnecessary horse traffic and keep your horse/s at home.

Monitor horse/s for spike in temperature Isolate sick or exposed horses

Vaccinate on risk-base

Immune Boosters on a risk-base



Mortality rates are high for the neurologic form of EHV-1



Again, this information is not meant to cause alarm but to inform you of the potential outbreak in our/your area. As we learn more information, we will pass it on to you. Be thoughtful of handling horses returning from events where there may have been exposure.



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