Many horse owners don’t know that there are at least four types of Equine Herpesvirus. The ones that we associate the most are EHV-1 and EHV-4. EHV-1 is the most prevalent and often the most destructive to the horse. EHV-1 causes severe respiratory problems, abortion in mares and neurological disease. EHV-4 causes upper respiratory infection only. Most horses, however, contract EHV-1 and is it usually first diagnosed by runny noses, fevers, coughs and broodmares that are aborting.
The neurological disease of EHV-1 is a mutant strain and has caused many stables and racetracks to have to be quarantined around the country. The University of Findley in Ohio has reported the most devastating outbreak of EHV-1 where one-third of the schools 140 horses displayed the neurological symptoms in 2003. Twelve of the horses died from the disease.
Once the virus has infected the horse, the horse will be a lifelong carrier. This is very similar to the herpes diseases found in humans. The horses may no longer show signs of being ill, but they will continue to shed the virus, especially during times of high stress. The horses sporadic shedding of the disease is often considered the cause of many outbreaks that occur randomly. Many veterinarians believe that nearly three-quarters of the equine population are thought to be carriers of the EHV-1 non-neurological form of the virus.
The disease is spread by infected horses through their respiratory secretions. Horses can contract the disease through nose-to-nose contact, sharing buckets, bits, lip chains and even on handlers. Once the virus has made it into the horse, the virus travels through the bloodstream. The early symptoms include nasal discharge and a slight increase in temperature. The fever does not remain consistent, so if you believe that your horse is showing symptoms, you will want to check their temperature every six hours. The nasal discharge will begin clear, but will turn to thick and milky. Your veterinarian can obtain swabs of the discharge and blood samples to test for the disease.
If the horse is infected with the neurological strain, the horse will begin to show symptoms in six to twelve days. The initial progression of the disease may happen quickly and within 24 to 72 hours. Fevers are generally over 102 degrees Fahrenheit and other symptoms include the nasal discharge, depression and loss of appetite. The first neurological symptoms may begin in the hindquarters and may include toe dragging, a floppy tail, incontinence and weakness in the hind legs. Eventually, the horse will not be able to stand. If the horse is down for more than twenty-four hours, it is not likely that they will survive the infection.
As the disease is caused by a virus, there is no cure for it. Many vets will give horses immune modulator shots that will help to boost their immune system and will help them to attack the disease through their own immunity. Many horses with only the respiratory problems will do well with the shots. Antibiotics are not going to generally help these horses, as they do not kill viruses, only bacteria. While the horse is ill with the respiratory condition, all that owners and vets can do is to treat their symptoms. Your vet will provide you with strong anti-inflammatory that lessens swelling and pain.
There are also no vaccines that are capable of preventing the neurological form of the disease. Studies have been done on small groups of horses to compare the effects of the modified-live vaccine versus the inactivated killed vaccine. The modified-live version of the vaccine seemed to be more effective to prevent the respiratory disease, while neither had an effect on preventing the neurological symptoms. The vaccine will help to minimize the spread of the virus.
To prevent your horses from becoming victims to EHV-1, it is recommended that your horses be placed on a food vaccination program as well as good herd management. The American Association of Equine Practitioners recommends that all pregnant mares be vaccinated in order to prevent abortions. Foals, weanlings, and yearlings should also be vaccinated. Foals should receive their first dose at four to six months, their second dose at five to seven months and their third dose at six to eight months. They should also receive the vaccinations at three-month intervals. Yearlings and performance horses should receive booster shots every three to four months or annually depending on the amount of stress that they are under. Broodmares should be vaccinated at their fifth, seventh and ninth months of gestation with the inactivated EHV-1 vaccine. You may also give them an optional dose at their third month if the mare is under stress. Mares should also be vaccinated before breeding and four to six weeks before foaling. Breeding stallions should also be vaccinated prior to the start of their breeding season as well as every six months.
Other preventative strategies include sanitizing your barn at least three times per year. Barns that have experienced outbreaks may sanitize six times per year. If you show horses and their was suspicion that horses at the show may have been sick with the virus, you will want to quarantine your own horses from the rest of the herd for up to twenty-one days. You will also want to disinfect every area of the barn which suspects sick horses have been housed or worked.
If an outbreak does occur at your barn, you will want to instruct all owners, handlers and visitors to wear leather or rubber boots that can be disinfected in chlorine or bleach. You should have disinfectant tubs located at every entrance to the barn. You will want to disinfect all stalls, floors, walls and possibly even arenas and fencing. Disinfect all grooming supplies, buckets, water troughs and tack that may have been shared. One horse in a large herd can spread the disease throughout the whole herd.