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EHV-1 spread slows - latest state by state wrap

June 1, 2011

By Laurie Dixon

» Updated wrap - June 3

State quarantines and hold orders appear to be working in limiting the spread of deadly Equine Herpesvirus 1 (EHV-1).

Death toll

As at 25.6.2011

New Mexico
About EHV

State updates are sporadic, perhaps indicating that no news is good news. Those that do update their information daily have reported limited developments in recent days.

Our state by state wrap of EHV-1 across western states reflects the latest report from the Animal and Plant Health Inspection Service (APHIS) of the US Department of Agriculture, dating from last Thursday.

Another full update is expected this Thursday.

The agency is collating all state information and is publishing it 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 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.


No update for some days. 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.


In its Tuesday update, the California Department of Food and Agriculture said there were 19 confirmed cases of EHV-1 in the state.

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

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. The 19th horse was exposed to one of the horses that went to Ogden.

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


As of Monday, there were nine confirmed cases of horses with EHV-1.

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

There remain 22 suspect cases - horses that are believed to have been exposed to EHV-1.

Twelve quarantine and hold orders have been issued in eight counties - Bent, Boulder, Garfield, Gunnison, Larimer, Mesa, Morgan, and Weld.

Thirty-eight horses were exposed from Ogden, and 78 were considered secondarily exposed in the state. Six of the cases involved neurological signs, APHIS figures show.

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."

He continued: "We are considering all of our options for protecting Colorado's horse industry. At this point, we do not believe it's necessary to stop horses from entering the state but we need to be able to know where those horses are coming from and where they are going; traceback is a vital part of disease control."


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.


Forty horses at Ogden, and 108 at risk because they were exposed to the horses returning from Utah. The last data found by Horsetalk showed seven suspected cases of EHV-1, and one confirmed case. Two horses are suspect for EHM and three have been confirmed. Two have been euthanized.


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 report there are no horses known to have been secondarily exposed. No suspected or confirmed cases.


In a May 24 update, the Missouri Department of Agriculture had 30 horses on a Boone County property under close observation and under a hold order, as three horses had returned to the property from the Ogden event. As of the above date, there had been no confirmed or suspected cases. The farm in question has been under a hold order since May 16. The latest APHIS information tallies with the above information, but no advances on this situation can be found.


Seventeen horses at Ogden, and one secondarily exposed. Good news for the state. One horse considered suspect for the disease returned negative test results. From May 22 to May 27 - the last reported update on the webpage of the Montana Department of Livestock - no cases have been reported or are suspected.


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. The latest APHIS information tallies with the above information.


Seven horses attended at Ogden, with 20 horses secondarily exposed on return home. As of May 25 - the state's latest update - 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 show only one confirmed case of EHV-1.

New Mexico

APHIS figures indicate 13 horses exposed at Ogden, with 26 considered secondarily exposed. In a May 26 update, state veterinarian Dave Fly said three premises were currently under quarantine as a result of what he called active cases of EHV-1. "All three premises have had cases of the neurological form of EHV-1, also known as Equine Herpes Myeloencephalopathy," he said. "One horse has died, two horses are clinically ill and one horse has recovered." The latest APHIS figures reflect this information.

The last case in New Mexico was reported on May 20. All other horses on these quarantined premises are under observation and are being monitored by their farm veterinarians.


Just one horse attended the Ogden event, but 32 have since been secondarily exposed. One property in Love County is under quarantine, with a horse confirmed as positive for EHV-1. It attended the Ogden event and was showing mild neurological signs. Other horses on the property remained healthy.


Twenty horses attended at Ogden, and 120 have been secondarily exposed, APHIS figures show. Four cases of EHV-1 have been confirmed. 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 over the weekend after developing neurologic signs, state veterinarian Dr Don Hansen has advised.

Test results from the horse were positive for EHM. This is the fourth confirmed case of EHV-1/EHM and the first EHM fatality in Oregon. This is not the same horse as the first reported case, which was also a horse from Clackamas County.

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 be advised.

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.


No reported developments since last Friday. One fresh cash of the neurological form of EHV-1 was reported that day by the Texas Animal Health Commission. Preliminary investigations indicate no connection to the Ogden event. A quarter horse racehorse stabled in Ector County, showed neurologic symptoms consistent with the disease, and ultimately tested positive for the disease. All horses on the premises are under quarantine. Authorities are gathering additional information to determine if any other horses were exposed.

Twenty-six horses went to Ogden, and 323 horses were considered to have been exposed secondarily. In that update, the commission said that 12 of the Ogden horses and 174 horses considered secondarily exposed remained under movement restrictions.

Just one horse in the state had previously been confirmed with the neurological form of the disease since the outbreak began. 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 commission said it continued to evaluate other unrelated horses with clinical signs.


Fifty-one horses went to Ogden and 162 are considered secondarily exposed. There are 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. Monday had also proved to be a good day, with all samples tested at the Utah Veterinary Diagnostic Laboratory in Logan being negative. Quarantines are in place for all horses either confirmed or suspected of having the disease. APHIS reports as follows: Four EHV-1 cases suspected, one confirmed, one suspected case of EHM and four confirmed. One horse dead.


Thirty-five horses went to Ogden. No information on the number of horses secondarily exposed. The latest information indicates seven horses have tested positive for EHV-1. The first case, at Washington State University's veterinary teaching hospital, has since been discharged. Three of them suffered the neurological form of the disease, APHIS figures show.

The College of Veterinary Medicine at Washington State University confirmed one more horse with EHV-1 on May 25. This brings the total number of horses now under isolation and care for the neurologic form of the viral disease at the university's veterinary hospital to three.

Confirmation of the third case came Wednesday, May 25, when nasal swabs administered to the horse, which is an inpatient in the WSU Veterinary Teaching Hospital, tested positive. The horse had been running a fever, but had not tested positive for the disease until today. Veterinarians said the case fits a common pattern for the development of the disease.

The total number of horses confirmed to have EHV-1 in Washington state now stands at seven, with no deaths. The ailing horses are located in Spokane, Thurston, Chelan and Asotin counties with one horse in each. Whitman County now has three, according to the Washington State Department of Agriculture.

This new confirmation at WSU means the restrictions for new, non-emergency horse or camelid patients coming to WSU's Veterinary Teaching Hospital will be in place for a minimum of 21 more days.

Emergency services are still available but owners must call ahead first to ensure the hospital can make special accommodations to protect any incoming animals. The phone number is 509-335-7073.

Washington State Veterinarian Dr Leonard Eldridge has suspended the state's exemption for horses entering Washington from Oregon or Idaho for up to four days. All equines entering the state must now require a current health certificate showing a current temperature reading, or enter using a six month passport.


State Veterinarian Dr Bob Ehlenfeldt said earlier this week that 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.

He did not recommend the cancellation of any scheduled shows, but reminded horse owners that biosecurity is always important "not just when there is an outbreak. They should always isolate horses returning from competitions, trail rides, or any other event where they come in contact with other horses."


Thirty-seven horses went to Ogden, with 16 horses considered secondarily exposed. There is one suspected case of EHV-1, APHIS figures show.



Four confirmed cases in all.

There is a confirmed neurologic case of EHV-1 in an Alberta horse that showed neurologic signs on May 1, 2011 and was isolated at that time. This horse did not attend the cutting horse show in Ogden that has been associated with the US outbreak of the disease. However, it had attended cutting horse events in Alberta. This horse has been under veterinary care and is recovering well. The origin of the source of contact for this horse remains unknown.

There is a second confirmed case of EHV-1 in another Alberta horse that first developed signs of fever and respiratory disease on May 14, 2011. There are no neurologic signs in this horse. This horse had contact with horses and tack that had previous contact with horses at the Ogden show. This horse is under treatment and isolation at this time.

There is a third confirmed case in an Alberta horse that first developed signs of fever and respiratory disease on May 16, 2011. Again, there are no neurologic signs in this horse. This horse travelled to the show in Ogden and returned to Canada on May 15, 2011. This horse is under treatment and isolation at this time.

The fourth confirmed case showed respiratory signs.

Veterinarians in Alberta and other Western provinces are holding regular conference calls to update the situation.

British Columbia

Three suspected cases were reported some days ago, with no horses reported to be exposed secondarily. These suspected cases, all on the same farm, were not confirmed by laboratory testing, but through clinical diagnosis. The three horses that returned from the Ogden show developed neurological disease and were being treated intensively as if they had the neurological form of EHV-1. Strict biosecurity procedures were put in place to prevent spread of this disease from the farm. No updates on this situation have been found.



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