September 19, 2011
The equine herpesvirus (EHV-1) outbreak traced to an April National Cutting Horse Association event in Ogden, Utah, is over, according to a June 23 U.S. Department of Agriculture Animal and Plant Health Inspection Service (APHIS) situation report.
Ninety cases of EHV-1, or equine herpesvirus myeloencephalopathy (EHM), were confirmed in nine states. Of the 90 cases, 54 were present at the Utah event. Thirteen horses linked to the incident died or were euthanized.
“Financial losses from this outbreak go deep into six figures, maybe more,” said D. Paul Lunn, BvSc, MS, PhD, MRCVS, Dipl. ACVIM, a professor and head of the department of Clinical Sciences at the Voss Veterinary Teaching Hospital in the College of Veterinary Medicine and Biomedical Sciences at Colorado State University in Fort Collins, Colo.
“That takes into considering event cancellations, the economic effect felt by communities in which the events would have taken place and treating sick animals. The USDA is conducting additional research on the outbreak which will offer a new analysis of the effect the outbreak had on the industry.”
Dr. Lunn said the NCHA behaved responsibly by acting quickly and effectively when the virus spread at its event.
“The NCHA canceled very large and expensive shows, particularly the event in Tulsa right after the Ogden event, which would have meant more disease spread,” Lunn said.
Experts say recovery from EHV-1 can take up to six months, but in most cases horses return to full function.
“Herpes gets incorporated into the host’s DNA, then under stressful conditions, activates and clinical signs become apparent,” said , PhD, owner of Killdeer Veterinary Practice in Killdeer, N.D.
“This outbreak differs from others because it originated at a predominant event, and infected horses incubated the virus while crossing over state lines, then passed it on to horses that were not at the event. Herpes is different than other viruses because it will live in the host for the duration of its life. Vaccines for herpes can mute clinical signs of an infection and reduce virus shed, but they’re not a cure-all.”
Dr. Lenz, a rural equine practitioner with EHV-1 experience, said horse owners and those involved with equine events have become complacent, thinking that vaccines will prevent or repair all disease and virus-related issues. But she notes that a proper vaccination regimen is only part of the complete disease-prevention protocol.
“Keeping each horse healthy and up-to-date on vaccines not only protects that animal, but it is also a practice of good herd health,” Lenz said.
“Veterinarians are an integral part of proper vaccine care. Many owners have a false sense of their horse’s protection when they personally vaccinate the animal. When a vaccine program is followed under a veterinarian’s order, the proper type of vaccine is given (killed or modified live) at the right times, is administered properly and there’s assurance that the vaccine was kept under the right storage conditions. If a problem does occur, the vet will have the vaccine’s lot number and can report issues to the company.”
Lunn said horses are exposed to EHV-1 in the first few weeks of life, and immunity is short-lived.
Horses need vaccinating up to four times a year to justify confidence in protection. Given the nature of this specific virus, veterinarians recommend aggressive preventives.
“We don’t know how long the vaccine lasts,” Lenz said. “It’s hard to determine because [the virus] can be dormant for such a long time. If horses aren’t vaccinated and they’re exposed to a horse shedding the virus, they’ll receive a high viral load. This outbreak was the mutant form of the virus. Neurologic symptoms can be present with an infected horse, and respiratory issues and fetus abortion can occur.”
Although current reports don’t specifically identify the direct cause of the spread of EHV-1 in Ogden, many professionals in the industry said prioritizing biosecurity measures is a must.
“Currently there is little opportunity with the way we do things to prevent spread,” Lunn said.
“Horses immediately go from one show to another or to farms. We really need to think about more containment and biosecurity with these events. When horses are moved from one event to another or when they’re home, they should be quarantined at least for a few days. Another big issue is that we desperately need a vaccine against this virus that works.”
Lenz said exercising proper biosecurity is the lesson to be learned from this outbreak.
“Disinfecting often and keeping symptomatic horses in quarantine is vital in stopping disease spread. Keeping horses healthy and stress-free prevents herpes activation. We have such great vaccines, people forget the importance of these other factors of disease control.”
Lenz hopes the value of lessons learned in the outbreak trumps the problems it caused.
“Hopefully the outbreak helped more than hurt,” Lenz said. “I hope owners are more educated and see the value in veterinarians’ programs. Awareness is good.
“More and more is taken out of veterinarians’ hands now in regard to vaccines and animal health. People forget these are biological systems and owners don’t understand how to handle vaccines. Why don’t we sell human vaccines over the counter? Because it’s a public health issue. Vaccines are a big money maker–everyone wants a hand in it, but it should be a veterinarian.”
On Sept. 23-28, the Dorothy Havemeyer Foundation Inc. will conduct an invitation-only workshop in Steamboat Springs, Colo., to discuss EVH-1 and developing a more effective vaccine against the virus.
The private foundation’s function is to conducts scientific research to improve equine health and welfare.
“The last meeting took place in 2008,” Lunn said. “Thirty to 40 academics got together to compare notes to effort to improve the situation. Out of the 54 vaccines with label claims including EHV-1 protection, none completely protect against the virus. There isn’t an effective anti-viral vaccine for humans, either, other than chicken pox. Viruses use strategies to degrease animals’ defenses against them. Every manufacturer that produces an EHV-1 vaccine is conducting research to improve vaccine potency.”
In view of the outbreak, Pfizer Animal Health and the Kentucky Thoroughbred Owners and Breeders developed a video posted on YouTube to educate horse owners on EHV-1.
The EHV video features Kenton Morgan, DVM, Dipl. ACT, a veterinary specialist at Pfizer Animal Health; Doug Byars, DVM, Dipl. ACVIM, Dipl. ACVECC, an expert in veterinary disease; and Craig Carter, DVM, MS, PhD, Dipl. Dipl. ACVPM, director of the University of Kentucky diagnostic laboratory and authority on testing EHV.
States with positive EHV-1 or EHM cases
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