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EHV-1: our latest state by state wrap

May 23, 2011

» State by state wrap III - 29 May

The following information on the outbreak of Equine Herpesvirus-1 in horses across the western states is based on official information only.

Death toll

As at 25.6.2011

New Mexico
About EHV

This information is based on data provided by the Animal and Plant Health Inspection Service (APHIS) of the US Department of Agriculture, which is co-ordinating the collating of data to present a clearer picture of the outbreak of the potentially deadly disease.

These figures have been adjusted in some cases, but only from official data from state agriculture departments, state livestock boards or state veterinarians.

EHV-1 is capable of causing severe neurological symptoms in horses, which can prove fatal. However, not all horses that are infected will show neurological signs. Those that do have what is known as Equine Herpes Virus Myeloencephalopathy, or EHM.

Horses with severe neurological signs are often unable to stand and are euthanized as a consequence.

Horses in the data below, described as secondarily exposed, are those that came into contact with horses after they attended the National Cutting Horse Association Western National Championships in Ogden, Utah from April 29 to May 8.

Authorities continue to warn that the strain at the centre of the outbreak is highly contagious and can prove fatal to horses.

They urge horse owners in affected states to avoid all non-essential horse movements, at least until the extent of the outbreak is clearer.

The following information will be updated as and when fresh information comes to hand.


Twenty-one horses were exposed at the Ogden, Utah, cutting horse event at the centre of the outbreak. Those horses returned home, and 67 horses are considered secondarily exposed. There are four suspected cases of EHV-1, three suspected cases of EHM and one confirmed case. One has been euthanized.


In all, 54 horses were exposed at the Ogden event. Latest information from the California Department of Food and Agriculture reveals 17 horses across 11 counties have been confirmed with EHM. The cases by country are Amador (1), Glenn (2), Kern (2), Los Angeles (1), Marin (1), Napa (1), Placer (3), Plumas (1), Shasta (1), Stanislaus (3) and Ventura (1). Sixteen of the confirmed positive EHM cases participated in the Ogden event. One of the confirmed positive cases participated only in the Kern County cutting horse event on May 13, held after the Ogden event. In Bakersfield, one horse has been euthanized after showing neurological signs.

Three confirmed positive EHM horses are being treated at the University of California Veterinary Medical Teaching Hospital in Davis. Seven positive horses have displayed neurological signs. The other cases have only shown with fevers.

All positive confirmed EHM cases are under a State Quarantine.


Thirty exposed from Ogden, and 68 considered secondarily exposed. Latest figures from the state agriculture department show 22 suspected EHV-1 cases, and nine confirmed. There are two cases of EHM, with two horses dead or euthanized. Twelve quarantine and hold orders have been issued in eight counties - Bent, Boulder, Garfield, Gunnison, Larimer, Mesa, Morgan and Weld.


No horses in the state are confirmed or suspected of havinging EHV-1 from the Ogden outbreak. However, in what state animal health authorites are describing as a separate incident, one farm in Alachua County is under state quarantine and two horses have been euthanized due to complications of EHV-1 infection. One case is confirmed, the other suspected. Authorities believe the index case occurred on the quarantined farm due to re-emergence of a latent infection and that no exposure has occurred off the affected premises.


Thirty-six horses potentially exposed, and 14 at risk because they were exposed to the horses returning from Utah. There are 13 suspected cases of EHV-1, but no confirmed cases. There are three suspected cases of EHM and one confirmed, with two horses dead or euthanized. No confirmed or suspected cases were added at the weekend.


Just one horse is known to have been exposed at the Illinois event, but nine horses were secondarily exposed. No evidence of any cases, according to APHIS.


Five horses exposed at Ogden, and 53 exposed secondarily. No suspected cases of either EHV-1 or EHM.


Nineteen horses attended the Utah event, but authorities do not believe any horses have been secondarily exposed. No suspected or confirmed cases.


Seventeen horses at Ogden, and one secondarily exposed. No suspected or confirmed cases.


Seven horses at Ogden. No data on whether any other horses have suffered secondary exposure. No suspected or confirmed cases, but five properties are under quarantine as a precaution.


Seven horses attended at Ogden, with eight horses secondarily exposed on return home. Three suspected cases of EHV-1 but no confirmed cases.

New Mexico

APHIS figures indicate nine horses exposed at Ogden. No information on potential secondary exposure of horses. Three cases of EHV-1 are suspected, one is confirmed. One case is known to be in the Albuquerque area and one in the Hobbs area.

There is one suspected cases in which a horse has neurological symptoms and one case of this form of the disease has been confirmed. One death.


Just one horse attended the Ogden event, but 32 have since been secondarily exposed. There is one suspected cases of EHM. The horse is showing mild neurological signs but is improving. Other horses on the property remain healthy and the property has been placed under movement restrictions.


Twenty horses attended at Ogden, and 120 were secondarily exposed. Two cases of EHV-1 have been confirmed. One is in Umatilla County, the other in Clackamas County. All horses either from the Ogden event or secondarily exposed are under quarantine in their stables.

EHM is now a reportable disease, requiring that the state veterinarian, Dr Don Hansen, be advised.

South Dakota

Four horses at Ogden. No suspected or confirmed cases.


Twenty-six horses went to Ogden, and 336 horses are considered to have been exposed secondarily. One horse is suspected of having EHM and one horse has been confirmed with this neurological disease. It is believed this was the horse that was taken for treatment at a West Texas vet clinic and was subsequently returned home, where it is under quarantine at its premises of origin.


Seven confirmed cases. The state has had its first fatality, reported by state veterinarian Bruce King on Saturday evening. He said the horse was found lying down in its stall in Utah County. All attempts to get the horse to rise were fruitless and it was euthanized. As of Friday evening, there were two additional confirmed cases of EHV-1 within the state, at two additional properties, both of which were placed under restrictions. One is in Weber County, the other in Kane County. The five other confirmed cases are in Utah County, at one property. This updates formal APHIS figures, which indicated two of these cases were suspected, but unconfirmed.


Thirty-four horses went to Ogden, but no horses are considered to have been secondarily exposed on return home. There is one confirmed case of EHV-1, four suspected cases of EHM and two confirmed EHM cases.


Seventeen horses were to Ogden, with 34 horses considered secondarily exposed. There is one suspected case of EHV-1.



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