caused by viruses transmit ed mostly by mosquitoes. Either disease can be serious, but EEE has a much higher fatality rate than WEE. Typical symptoms of Eastern
Equine Encephalomyelitis include loss of appetite, fever and change in behavior. Within 12 to 24 hours of the initial symptoms, the horse will exhibit head pressing, circling and will oſt en become blind. As the disease progress- es, the horse may become recumbent and might suff er seizures. In the worst cases, horses die from respiratory ar- rest two to three days aſt er the onset of clinical signs. T e fatality rate for horses with EEE
may be as high as 90%. Horses that do survive are frequently leſt with perma- nent neurological impairment. Treat- ment is mainly supportive, as there are no anti-viral drugs available for EEE. Fortunately, EEE is relatively rare and is generally restricted to the eastern, southeastern and some southern states. Western Equine Encephalomy-
a disease. Says Dr. Wright, “T e EIA virus is mechanically transmit ed from one horse to another by bloodsucking horse fl ies, deer fl ies (Tabanids), stable fl ies (Stomoxys spp.), mosquitoes and possibly midges. For transmission of the EIA virus to occur, the horse fl y (vector) must fi rst fi nd and begin feeding on an infected horse, be inter- rupted in its feeding and then transfer the virus during a subsequent feeding on a susceptible horse. Feeding must occur within a short period of time.” The first symptom of EIA is usu-
Bites from summer-loving insects such as midg- es, mosquitoes and black fl ies can cause varied dermatological reactions in diff erent horses. While one horse may not be bothered much by multiple bites of a given species, another
elitis manifests quite diff erently. Aſt er an incubation period of one to three weeks, horses will develop a fever of up to 105 degrees. In many cases, this will be the only sign, as the horse’s natural immune response will clear the virus from the body within 48 hours aſt er the onset of the fever. If the horse is unable to clear the virus, the situation becomes much more serious. T e central nervous system is at acked, resulting in symptoms that include agitation, compulsive walking and circling and sometimes crashing into walls. T is stage is followed by extreme depression, reluctance to move and drooping posture. T e horse may also have tremors, diffi culty swallowing and an uncoordinated gait. If the horse remains standing, it may fully recover, but horses that
become recumbent have a poor prognosis. Overall, the fatality rate for WEE is close to 50%. WEE is the most common strain of equine encephalomyelitis, with outbreaks recorded in the western and mid- western states. Variants of WEE have also caused sporadic cases in the northeast and southeast. T e risk of exposure and the geographic dis- tribution of WEE and EEE vary from year-to-year, depending upon the distribution of mosquitoes and birds that act as reservoirs for the virus. To reduce the likelihood of horses contracting WNV, WEE or EEE,
the American Association of Equine Practitioners (AAEP) advises vac- cination of all horses against these diseases. In addition, a good health program will include minimizing your horse’s exposure to mosquitoes and mosquito control. To reduce mosquito exposure, stable horses at dusk and dawn; use fl y sheets, masks and leg wraps; turn barn lights off ; use fans to move air; and use mosquito repellents. Mosquito control programs include reduction of standing water, encouraging natural predators (fi sh, birds, etc.) and use of chemicals for larval and adult mosquito control. Other serious diseases may be spread not only by mosquitoes but
also by biting fl ies. Equine Infectious Anemia (EIA), also called swamp fever due to the higher incidence in warm, wet areas, is just such
56 | June 2013 •
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may have a marked reaction to even one bite. Photo by Ann Jeff ree
ally fever, which comes on seven to 30 days aſt er infection. In most cases, the initial fever goes undetected, and the disease is not recognized until it becomes chronic and the symptoms are more obvious. As Dr. Wright ex- plains, “Chronically infected horses experience episodes of fever, weight loss, depression, progressive weakness, anemia and edema. T ese signs occur every two weeks in recurring cycles. Other symptoms which may occur during the course of the disease include loss of appetite, frequent urination, diarrhea, weakness, paralysis of the hindquarters, paleness of the mucous
membranes, yellowish discoloration of the conjunctiva, small pinpoint hemorrhages beneath the tongue, rapid breathing and accelerated pulse. Pregnant mares may abort.” Any symptomatic episode can be fatal, even if the horse has survived many of them in the past. An unusual characteristic of the EIA virus is that it remains
permanently in the body. T erefore, even though a horse may be in symptom-free remission, it is still a source of possible infection for other horses. Because of this, recommendations are that aff ected horses be euthanized or permanently segregated in a fl y-proof enclosure. Un- fortunately, there is currently no vaccine available to prevent EIA and no specifi c treatment for the disease. What we do have is the Coggins test, a blood test that detects antibodies to the EIA virus. Utilization of the Coggins test has helped reduce the incidence of EIA, and many facilities now require a negative Coggins test certifi cate before a horse is allowed onto the property.
continued on page 58
STATS 54%
from our trailBLAZER readers
said they have had a horse who suff ered from summer allergies
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