At least three horses, over a period of five days in mid-March, were euthanized due to EHV-1, the “neurotropic” strain of the Equine Herpes Virus that has reared its ugly head in hot spots around the country since December of last year. (California Riding Magazine, Feb. 2007)
The three horses were from two boarding facilities in Montara, in the North California coastal community near Half Moon Bay.
Well-known and respected horsewoman Debra Titone owns Renegade Ranch in Montara. She witnessed first hand the progression of the disease in two of these ill-fated horses.
“The first mare first showed symptoms on Mon., March 5,” Titone reports. It was initially diagnosed and treated as a less threatening virus. But, by March 12, the mare was down and demonstrating clear neurological symptoms. “When the horse tries to stand up, they tend to sit on their hind quarters and literally spin around,” Titone explains. “It’s because this disease affects their neurological system, their spinal cord, starting with the tail end.”
The mare was taken to U.C. Davis the next day, followed by another mare whose experience with EHV followed a much faster course. The second mare, Titone reports, went from seeming normal to “hanging its tail, stumbling, having trouble urinating and going down” within two hours. Neither horse improved after getting to Davis, and on Wed., March 14, the owner decided to have both euthanized. These two horses lived in the same pasture, but a third horse in the same pasture appeared fine as of March 16.
On Mon., March 12, two other horses at Renegade Ranch exhibited EHV-1 signs. They were immediately tested through nasal swabs. Reflecting the complexity of this disease, Titone relays that the horse exhibiting the most severe signs tested negative, while the other horse with fewer symptoms tested positive. Both horses were started on Veltrex, an anti-viral drug that can reduce symptoms but is neither a cure nor a vaccine. Both were doing well as of Fri., March 16.
Valtrex (Valcyclovir) is typically given twice a day after diagnosis. A course of treatment costs approximately $3,000 and does not ensure survival. At least two of the horses who died had started treatment.
On March 13, Renegade Ranch and neighboring Moon Valley Ranch put their facilities on quarantine. Stables and private barns throughout the area did the same as word spread.
Veterinarians Address Worried Owners
An informational meeting was quickly organized for the evening of March 16. Dr. John E. Madigan of the U.C. Davis Department of Medicine and Epidemiology and Dr. Gregory L. Ferraro, Director of the U.C. Davis Center for Equine Health; along with Dr. Wayne Browning and Dr. Philip Bellamy of the Bayhill Equine veterinary practice in Redwood City, addressed an impromptu crowd of more than 100 concerned owners of horses boarded in the coastal area of Half Moon Bay.
According to Madigan, California is a voluntary quarantine state and he opened his remarks by saying that he was “very impressed with the level of cooperation between ranch managers and horse owners to control this outbreak and impressed with the response of this horse community.” He reassured horse owners that the disease is spread mainly by direct contact and encouraged people to wash their hands frequently and to not move amongst multiple horses. While this strain has been around for 35 years, breakouts are relatively rare.
Madigan cautioned against running PCR (polymerase chain reaction) tests without first identifying a fever because a small amount of the virus is found in 80 percent of horses. It’s more important to detect the “viral load” which will be in the millions in a horse experiencing the full-blown disease. The team addressing the group reiterated several times the importance of taking the horse’s temperature twice a day if exposure is suspected. The initial fever spike may only last 12-24 hours and is defined as over 101.1 degrees. Temperatures should be taken again in a couple of hours if the trend is upward, the vets advised.
The veterinary experts appeared relatively confident of the containment of the disease given the voluntary quarantine conditions of the majority of the ranches on the coast. They felt they would know more in a few days about the long-term implications.
Horse owners throughout the area had been on high alert throughout March. The meeting helped worried horse owners sort rumor from fact and continue with voluntary quarantine and bio-security measures.
“Moss Beach and Montara are eerily quiet,” reports staff writer Nan Meek, who keeps her horse at private barn in the area. “No groups of riders trailing down the shoulder of these rural, winding roads, no trail riders winding their way through the coastal hills. I never realized how much riding activity there was until everyone voluntarily quarantined themselves on their ranches, irrespective of whether their ranch had an EHV outbreak or not. None of us are 100 percent sure if our horses have been exposed or not, so we are all taking precautions.”
These key points regarding detection and containment emerged from the meeting:
• Fever can last from 12 hours to a week.
• Research shows that shedding of the virus stops 14-21 days after the time of the last fever. After that, horses can be moved freely with no chance of reactivation. This was proven by outbreaks among racehorses.
• It is not known why some horses get it and some don’t. It does not seem to be tied to history of vaccinations.
• Sunlight kills the virus. Wash your hands. Don’t share water buckets. Madigan said it cannot be moved by shoes or car tires. Some reports indicate that the virus is too heavy to be airborne, and others indicate it can be airborne a relatively short distance but does not live long once it “lands.”
• The vets suggested not vaccinating horses during an outbreak, as vaccinations cause fever and may make diagnosis difficult.
• A horse can be “shedding” the virus through nasal passages up to 12 hours before they spike a fever, hence the need for quarantine at a facility with a known case.
Symptoms
The initial clinical signs of the infection may be nonspecific and include fever of 102ºF or greater. Fever may be the only abnormality observed. Other presenting signs may be combinations of fever and respiratory symptoms of nasal discharge and cough. Some horses have reddish mucous membranes.
Horses with the neurological form of EHV-1 can soon become uncoordinated and weak and have trouble standing. Difficulty urinating and defecating may also occur. Often the rear limbs are more severely affected than the front.
Signs of brain dysfunction may occur as well, including extreme lethargy and a coma-like state. The incubation period for the infection is two to eight days. Once a fever occurs, clinical signs can progress to nervous system involvement over the next one to seven days.
Resources
• www.sfhorsemen.org. Great source for updates on Bay Area situation.
• www.vetmed.ucdavis.edu/ceh/topics-EHV-1-control.htm
• www.vetmed.ufla.edu