Dr. Catherine Kohn Veterinarian
Wednesday May 18, 2005
Dr. Catherine Kohn, a specialist in internal medicine and a professor in the Department of Clinical Sciences at The Ohio State University School of Veterinary Medicine, will answer your questions about equine herpesvirus (EHV) today from noon-1 p.m. She joins senior correspondent Steve Haskin, who will answer questions about horses preparing for this Saturday’s Preakness Stakes (gr. I).
Dr. Kohn is not directly involved with the situation at Churchill Downs that has led to a quarantine of three barns, but she has first-hand experience working during a herpesvirus outbreak in Ohio.
And now a few questions for Dr. Kohn.
How can my horse be exposed?
EHV-1 establishes a latent infection in all affected horses. The trigeminal ganglia in the brain is one site of latent EHV-1 infection. Factors that induce recrudescence of EHV-1 infection are incompletely understood: concurrent disease and “stress” are suggested to be important, and experimentally, administration of dexamethasone (steroid) has been shown to cause re-activation of the virus (Edington 1985). Re-activation of latent EHV-1 is associated with shedding of the virus in nasal secretions and may result in spread of infection to naive young horses. This method of recruitment of new hosts, combined with short-lived protection after infection, and the frequency of of subclinical infections, has made EHV-1 endemic in horse populations. Community acquired infection is thus always a possibility.
During an outbreak of EHV-1 disease, nasal secretions may transmit the virus in aerosols created when the affected horse coughs. Fetal tissues, placenta and uterine fluids from mares that abort are also infective. Contaminated feed and water may also spread the virus. Common airspaces allow dissemination of the virus to horses sharing the airspace. The virus can also be transmitted on hands, grooming implements or buckets (fomites). Experimentally, transmission has occurred over a distance of 35 feet. The source of the virus is usually in apparent horse carriers.
How long does it take to know if my horse is going to be sick?
If your horse has been exposed to EHV-1, and especially if your horse is exposed during an outbreak of EHV-1 where multiple horses are affected, we recommend that you quarantine your horse at least 21 days. If the horse dies not show evidence of disease (fever, cough, nasal discharge, or signs of neurological impairment such as weakness, stumbling, urinary incontinence) after 21 days it is unlikely that it will become ill. However, if your horse has been exposed during a major outbreak, we recommend that the premises be quarantined for 30 days after the last evidence of active disease ( as described above). Therefore, a prolonged quarantine maybe imposed, as new cases of fever , respiratory or neurological signs may develop as the outbreak progresses. Your horse would be required to remain on the affected premises during this entire quarantine period in order to reduce the risk of spread of the disease.
If a person had a horse in training at Churchill in a currently non-quarantined barn, how worried should they be?
The presence of virus at Churchill Downs is obviously a risk for every horse on the racetrack. However, attention to detail in setting up and enforcing the quarantine procedures can greatly reduce the risk of spread of the virus. I offer the following suggestions
1. Strictly control flow of traffic (equine and human) into all barns and stable areas not currently in quarantine. Horses in the quarantined barns should stay there. Persons who must enter the quarantined barns should wear barrier clothing at all times and should not go to other barns unless absolutely necessary. If a person must go from the quarantine area to another barn, a complete change of clothing and footwear is advisable. If possible the person should shower before changing clothes. At a minimum wash hands and arms with antiseptic soap. Please note that these suggestions apply to ALL personnel including but not limited to grooms, veterinarians, owners, and blacksmiths.
2. Take your horse’s temperature twice a day. If the horse has a fever (>101 F), a cough, nasal discharge, or weakness, or urinary incontinence, immediately report these findings to the Biosecurity Officer at Churchill Downs and to the Veterinarian in charge. It is imperative that sick horses and horses in close contact with them be quarantined. If everyone at the track follows these procedures, unaffected horses will be safer. Team work is essential to reduce the risk of spread of disease. Prompt veterinary evaluation of all possibly affected horses is crucial. Blood tests can help to determine if your horse is infected.
3. Remember that EHV-1 is common in horse populations. Inapparent carriers are most likely the source of infection and infection is lifelong.
Grand Rapids, MI:
Should I ship my horse away from an outbreak situation (racetrack, farm, training center) if it isn't in a quarantined barn?
This is an excellent question. Assuming that your horse has not been in a quarantine area, the Biosecurity officer may permit movement of your horse away from a facility where an outbreak is on-going. However, as a responsible horse person, one must consider the risk, which may be small, of your horse transmitting the virus to a previously uncontaminated facility. We all have the common goal of reducing the spread of the virus. It may be ethically preferable to leave your horse at the site of the outbreak until the quarantine is lifted. This conservative course of action minimizes any risk of spread of disease. Consult the Biosecurity officer and your veterinarian about the risk of your horse spreading virus.
Dr. Kohn, I read that some of the horses that were infected with the equine herpesvirus were destroyed. What circumstances indicate that this is the best course of treatment, or is it strictly a business decision?
Horses that have EHV-1 respiratory infection almost always recover completely. Horses that have EHV-1 neurological disease may have very severe impairments. These impairments may include inability to stand, difficulty breathing and severe respiratory distress. Horses with EHV-1 that are unable to stand have a very poor prognosis for life. Severely affected horses may be destroyed because their quality of life is unacceptably low and the likelihood of curing them is small. Many horses will recover from less severe neurological disease with excellent care.
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