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Federal EHV-1 update: our latest state wrap

June 3, 2011

By Laurie Dixon


Federal authorities in the US have today released their weekly Equine Herpesvirus-1 update, reporting one additional death and nine extra confirmed cases.

Death toll

As at 25.6.2011

New Mexico
About EHV

There remain 73 cases considered suspect and, in total, 244 properties across 10 states have horses that have been exposed.

Our state by state wrap of EHV-1 across western states reflects today's report from the Animal and Plant Health Inspection Service (APHIS) of the US Department of Agriculture.

The agency is collating all state information and is publishing it only when the data is verified.

Information below from individual states is included where it advances the details provided by APHIS.

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 show neurological signs 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.


Thirty-three horses were exposed at the Ogden, Utah, cutting horse event at the centre of the outbreak. There are two confirmed cases of EHV-1 infection and one confirmed cases of the neurological form, EHM. One has been euthanized. The state has four suspected cases of EHV-1


In its Thursday update, the California Department of Food and Agriculture said there were 20 confirmed cases of EHV-1 in the state.

The positive confirmed cases are located in the following 13 counties: Amador (1), Colusa (1), Glenn (3), Kern (2), Los Angeles (1), Marin (1), Napa (1), Placer (3), Plumas (1), Sacramento (1), Shasta (1), Stanislaus (3) and Ventura (1).

The last confirmed case was on May 31.

In all, 59 California horses were exposed at the Ogden event.

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 in Bakersfield on May 13, which was after the Ogden event.

In all, 628 horses in the state were considered to have been secondarily exposed.

Today's APHIS figures showed one fewer confirmed cases than the state agriculture department update.

Two horses have been euthanized in the state.


Today's APHIS figures showed there were 45 horses that attended the Ogden event. Nine horses are confirmed EHV-1 and seven have EHM among this number. Of the 78 horses considered secondarily exposed in the state, one has been confirmed with EHV-1.

Two horses which tested positive were euthanized after showing severe neurological signs associated with the disease.

There remain 22 suspect cases.

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 having EHV-1 from the Ogden outbreak. However, in what state animal health authorities 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-eight horses at Ogden, and 122 at risk because they were exposed to the horses returning from Utah.

APHIS figures show nine horses confirmed as positive for EHV-1, with another two confirmed with EHM among those that attended the event directly. Two have been euthanized. There are eight suspected cases.

Among the 122 secondarily exposed, four have been confirmed with EHV-1 and two with EHM. Eighteen are considered suspect.


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 the latest APHIS data.


Five horses exposed at Ogden, and 53 exposed secondarily. No suspected cases of either EHV-1 or EHM, according to the most recent data.


Eighteen horses attended the Utah event, but APHIS reports there are no horses known to have been secondarily exposed. No suspected or confirmed cases.


Three horses attended the Ogden event, but no suspected or confirmed cases have been reported, the latest APHIS information shows. The Missouri Department of Agriculture had 30 horses on a Boone County ranch under close observation and under a hold order, as the three horses had returned to the property. The farm in question has been under a hold order since May 16.


Seventeen horses at Ogden and no animals are now considered secondarily exposed. No cases have been reported or are suspected, according to APHIS data.


Seven horses at Ogden. No horses are known to have suffered secondary exposure. No suspected or confirmed cases, but five properties are under quarantine as a precaution, according to state officials. The latest APHIS information tallies with this information.


Seven horses attended at Ogden, with 20 horses secondarily exposed on return home. There were three confirmed cases. The first confirmed case of EHV-1 was in Elko County. The horse was said to be recovering, having suffered what the Nevada Department of Agriculture described as a mild form of the disease. The other cases are in Washoe County. They were exposed to two horses that attended the Ogden event. The event horses did not develop disease, however their stablemates exhibited neurological signs.

The latest APHIS figures tally with this information.

New Mexico

Latest APHIS figures show 13 horses exposed at Ogden, with 26 considered secondarily exposed.

Two horses are confirmed with EHV-1 and one with EHM. There is one horse considered suspect for EHV-1 and one considered suspect for EHM. One has been euthanized.

Among the 26 secondarily exposed horses, one has been confirmed with EHM and one is considered suspect for the neurological form. An additional horse is considered suspect for EHV-1.


Just one horse attended the Ogden event, but 32 have been secondarily exposed, latest APHIS figures show. One property in Love County was under quarantine, with a horse confirmed as positive for EHM. It was the animal that went to Ogden and was showing mild neurological signs. Other horses on the property remained healthy, state officials said. There are no suspected or confirmed cases among the 32 horses considered secondarily exposed.


Twenty horses attended at Ogden, and 140 have been secondarily exposed, APHIS figures show. Of the 20 that attended, two are confirmed with EHV-1 and one is confirmed for EHM. Two horses are confirmed for EHV-1 among the 140 secondarily exposed animals.

One is in Umatilla County, one in Clackamas County, the other in Deschutes County. Another horse in Clackamas County, who also attended the Ogden show, was euthanised last weekend after developing neurologic signs, state veterinarian Dr Don Hansen has advised. The location of the fifth horse is not available.

All horses either from the Ogden event or secondarily exposed are under quarantine in their stables.

There are no suspected cases.

South Dakota

Four horses at Ogden. Laboratory analysis has confirmed one case of EHV-1 in a horse in Gregory County, according to state veterinarian Dustin Oedekoven. The horse was not taken to the Ogden event, he said. The affected horse and others on the same property are under quarantine. The APHIS summary does not show this case, perhaps indicating the case is unrelated?


Eleven of the 26 horses in Texas that attended the Ogden event remain under movement restriction, the Texas Animal Health Commission reports. The number of stablemates under movement restriction has dropped from 323 to 171.

There are now a total of seven premises that have been exposed in the following counties: Randall, Parker, Jack, and Mills counties.

None of the Texas-origin horses from the Ogden event has been confirmed to have the neurologic form of EHV-1 so far, but one was returned to New Mexico after being taken to treatment at a Texas vet clinic.

The commission said it continues to investigate one confirmed case of the neurologic form of EHV-1 in a quarter horse racehorse stabled in Ector County. The animal is not connected to the Ogden event. The affected horse displayed neurologic symptoms consistent with the disease, and ultimately tested positive for EHV-1. All horses on the premises are under quarantine.


Fifty-one horses went to Ogden and 162 are considered secondarily exposed. Among the 51 Ogden horses, four are confirmed with EHM and one is confirmed with EHV-1. One has been euthanized. Four horses are considered suspect for EHV-1 and one is considered suspect for EHM.

Among the 162, three are positive for EHV-1 and one which was suspect for EHM was euthanized. Two are considered suspect for EHV-1.

State information shows four premises are affected, in Box Elder, Davis, Kane and Utah counties.

The two horses were euthanized after going down and being unable to return to their feet.


Thirty-five horses went to Ogden. No information on the number of horses secondarily exposed.

The latest APHIS information shows, among the 35 at Ogden, five are positive for EHV-1 and three are positive for EHM. There are no suspected cases among this group.

Affected counties are Spokane, Thurston, Chelan Asotin counties and Whitman.


State Veterinarian Dr Bob Ehlenfeldt said show organizers reported that two horses from Wisconsin were among those who attended the Ogden show. "As it turned out, the two horses were owned by Wisconsin residents, but kept in another state, so they did not enter Wisconsin after the show," Ehlenfeldt said.


Thirty-eight horses went to Ogden, with 17 horses considered secondarily exposed. There is one suspected case of EHV-1, APHIS figures show.



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