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EHV-1: State by state version III

May 24, 2011
Updated 7.09pm NZT

» Latest update

Our state by state wrap of the Equine Herpesvirus-1 outbreak across Western states has been updated by whatever official information we could find. The death toll currently stands at nine.

Death toll

As at 25.6.2011

New Mexico
About EHV

Some states have not updated their position online for some days.

The Animal and Plant Health Inspection Service (APHIS) of the US Department of Agriculture is now collating all state information and is publishing it when the data is verified. There has been no update for several days.

However, some states have updated their position and the following information reflects that, where we could find it.

With states having different political structures around their management of animal health, readers are very welcome to email us to point us in the direction of updated official information that advances the information below.

Please note that this information is based on original APHIS data, but 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, released midday local time, reveals 18 horses across 12 counties have been confirmed with EHV-1. This is an increase of one on yesterday. The cases by county are Amador (1), Glenn (2), Kern (2), Los Angeles (1), Marin (1), Napa (1), Placer (3), Plumas (1), Sacramento (1 - the latest case), Shasta (1), Stanislaus (3) and Ventura (1). Sixteen of the confirmed positive EHV-1 cases participated in the Ogden event. Two 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. The Department of Food and Agriculture described all 18 horses as confirmed for EHM, but said only seven positive horses had displayed neurological signs. Ten cases have shown only with fevers, while one horse displayed no clinical signs.

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. State veterinarian Keith Roehr says: "This disease can have tremendous affects on the horse community and I encourage horse owners to be vigilant about the disease prevention methods they use within their premises."


No horses in the state are confirmed or suspected of having 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. This information is now likely to be out of date.


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. Good news for the state. One horse considered suspect for the disease returned negative test results. There are currently 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. One confirmed case of EHV-1, in Elko County. The horse is said to be recovering. This would, based on APHIS data, appear to leave two suspected 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 case in which a horse has neurological symptoms and one case of this form of the disease has been confirmed. One death.

Authorities are concerned in that several horses attended the show but were not entered. There is therefore no record of these horses.


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. Three cases of EHV-1 have been confirmed. One is in Umatilla County, one in Clackamas County, the other in Deschutes County. The three horses tested positive for the virus but did not show any neurological signs. The state's Animal Health and Identification Division said all positive horses were directly linked to the Ogden event.

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. Laboratory analysis has confirmed one case of EHV-1 in a horse in Gregory County. The horse was not taken to the Ogden event, state veterinarian Dustin Oedekoven said. The affected horse and others on the same property are under quarantine.


Twenty-five horses went to Ogden, and 336 horses are considered to have been exposed secondarily, the Texas Animal Health Commission says. One horse is confirmed with the neurological form of the disease. This animal 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. The state had a single "suspect" case, reported last Thursday. The horse tested negative for EHV-1, but was euthanized because of the severity of its symptoms caused by an unrelated illness. The commission said it continued to evaluate other unrelated horses with clinical signs, but no additional cases had been confirmed as of late Monday.


Seven confirmed cases and eight suspected cases on a total of four premises, according to the latest information from state veterinarian Bruce King.

The four premises have been quarantined. They are in Box Elder, Davis, Kane and Utah counties. An earlier report that a property in Weber County was quarantined was incorrect, King said. That property was in fact in Davis County. Two horses have been euthanized after going down and being unable to return to their feet. At least five of the confirmed cases are in Utah County, at one property. This updates formal APHIS figures, which indicated two of these cases were suspected, but unconfirmed. As of 6pm on Monday, all samples tested during the day at the Utah Veterinary Diagnostic Laboratory in Logan were negative. This meant no new cases were confirmed for the day.


Thirty-four horses went to Ogden, but no horses are considered to have been secondarily exposed on return home. The latest update from state veterinarian Leonard Eldridge on Monday are are that six horses have tested positive for EHV-1. He did not indicate how many of these horses showed neurological signs, but earlier information with APHIS indicated there four suspected cases of EHM and two confirmed EHM cases.


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



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