What are Eastern Equine Encephalitis?
Horses, humans, pigs, rodents, white-tailed deer, and a variety of wild birds are susceptible to a virus known as Eastern equine encephalitis. It is a dangerous virus that can affect the central nervous system and cause brain damage and death. The mortality rate is high for most mammals that contract this disease, but highest for animals in the equine family, with a mortality rate that hovers around 90%. This disease is contracted through the bite of a female mosquito, and is not transmittable from horse to horse, man to horse, or horse to man.
Eastern equine encephalitis, also known as Triple E, is a dangerous mosquito-borne virus that infects not just horses, but humans, pigs, rodents, white-tailed deer, and a variety of wild birds.
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Symptoms of Eastern Equine Encephalitis in Horses
The onset of symptoms starts with a fever that may reach as high as 106 degrees Fahrenheit for one to two days. One to three weeks later, additional symptoms caused by the fever and brain lesions begin to develop and can include:
- Abnormal gait
- Aimless wandering
- Difficulty breathing
- Drooping ears
- Head pressing
- Inability to swallow
- Sensitivity to sound
Eastern equine encephalitis is very closely related to both the Western and Venezuelan equine encephalitis, but there are some differences between the three.
- Eastern equine encephalitis - Also known as sleeping sickness, this is the most virulent of the three strains of equine encephalitis
- Venezuelan equine encephalitis - More common in Central and South America than in North America; in 1995, one of the more recent outbreaks in Venezuela and Columbia sickened and killed several humans and hundreds of horses
- Western Equine Encephalitis - Western Equine Encephalitis (WEE) is very similar to its Eastern counterpart but the symptoms often wane after the fever is over rather than progressing to the more advanced symptoms
Causes of Eastern Equine Encephalitis in Horses
Eastern Equine Encephalitis is transferred to either humans or horses through the bite of a mosquito. Infections are most common from early spring until late summer, particularly if the spring and summer were preceded by a warm winter. This virus does not reproduce in sufficient amounts in mammals to make the animal directly infectious. Any horse can contract EEE but horses between the ages of six months and two years seem to be particularly at risk.
Diagnosis of Eastern Equine Encephalitis in Horses
The symptoms of this virus follow a well defined path so combining those symptoms with the time of year that they occurred may suggest an insect borne virus, but it is certainly not the only disease with similar symptoms. This virus is usually identified by utilizing standard blood tests such as a complete blood count and a biochemistry panel, as well as more specialized techniques, such as virus isolation. These tests are done in an attempt to differentiate Eastern equine encephalitis from other diseases and viruses that have some of the same symptoms. Some of the diseases that may present with similar symptoms can include:
- Chronic wasting disease
- Equine leukoencephalomalacia (moldy corn poisoning)
- Equine protozoal myelitis (EPM)
- Infectious anemia (EIA)
- West Nile Virus
Treatment of Eastern Equine Encephalitis in Horses
There is no actual treatment for Eastern equine encephalitis as it is not susceptible to any known anti-viral medications. Treatments provided for animals with EEE are mainly symptomatic and supportive. Supportive treatment measures could include fluid management to prevent dehydration and electrolyte imbalances, supplemental oxygen, or anti-inflammatory or anti-convulsant medications. Although Eastern equine encephalitis is not transferrable between horses it often occurs in groups as there may be several infected mosquitos in the area. The best way to protect yourself and the rest of your herd is to use mosquito control methods. Some of the steps you can take to reduce the number of insects in your barns and pastures include:
- Avoid evening and night time turn out in the pasture, particularly if the pasture is near a lake or pond
- Install a bird or bat house near the property, or in proximity to lakes or ponds on the property. Birds and bats are voracious predators of flying insects such as mosquitos
- Reduce the lights at night
- Remove standing water, be sure to empty buckets and clean water troughs regularly and ensure that damp vegetation is also removed from the stable area
- Spray the barn area with a suitable insecticide
- Use an insect repellant formulated for equines and designed to repel and kill mosquitos
Recovery of Eastern Equine Encephalitis in Horses
The prognosis for a human with Eastern equine encephalitis is guarded as approximately 35% of humans succumb to the disease, and another 35% of those who recover experience brain damage. In equines, the prognosis is poorer with the fatality rate reaching 90% or higher during most outbreaks. The best way to protect your horse is to get it vaccinated. Like another mosquito borne virus, West Nile, there is no viable human vaccine, but the vaccine that is given to equines is quite effective. Foals should be vaccinated at 4,5, and 6 months, with a booster 6 months later. The Triple E vaccine should be repeated at least annually for maximum protection.