Eastern Equine Encephalitis - Symptoms, Treatment and Prevention

By Ana Diaz Maqueda, Biologist specialized in ethology. August 8, 2019
Eastern Equine Encephalitis - Symptoms, Treatment and Prevention

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Eastern equine encephalitis is an extremely serious viral disease which affects horses. Unfortunately, it is also a zoonotic disease. Zoonoses are diseases which can be spread to humans. Eastern equine encephalitis, often known simply as EEE is a disease which is often first transmitted by other animals such as birds. The birds will carry the disease, but will do so asymptomatically. This means they will not suffer sequelae, i.e. consequences of the disease. When the disease is transferred to horses, the results can be fatal. The same when the disease is transferred to humans.

AnimalWised looks into everything you need to know about eastern equine encephalitis, especially its symptoms and treatment. While knowing about treatment for equine encephalitis is important, so too is prevention.

What is equine encephalitis?

Eastern equine encephalitis is also known as Triple E, EEE or even sleeping sickness. It can affect horses, hence the term ‘equine’m but ti also affects humans, birds, reptiles and other mammals. This is a zoonotic disease, transferable to humans and very affecting if it does spread.

Equine encephalitis has three main variations, eastern equine encephalitis (EEE), western equine encephalitis (WEE) and Venezuelan equine encephalitis (VEE). All three types of equine encephalitis are present on the American content, from North to South, but some have more prevalence in one area over another. They are caused by viruses of the genus Alphavirus, a group of about 30 viruses which affect vertebrates.

Eastern and western varieties are more pathogenic and harmful to the three groups of animals it affects. On the other hand, Venezuelan equine encephalitis seems to be divided into various subtypes. They are generally less virulent and only a few affect horses and humans.

Eastern Equine Encephalitis - Symptoms, Treatment and Prevention - What is equine encephalitis?

Causes of equine encephalitis

The viruses that cause equine encephalitis all belong to the same genus. These viruses are not very resistant in the external environment, so they do not take long to become denatured when outside of an infected body. This is why they will often require a vector to transfer the disease and infect someone else.

These viruses live inside some genera of some mosquitoes which only parasitize wild and domestic birds. In principle, these birds become reservoirs of the disease asymptomatically and do not bite a human or other animal (including horses). The problem lies when temperatures rise in the region where these mosquitoes live. It leads to other mosquito genera appearing which cannot survive in low temperatures. These new mosquitoes do bite birds, but they also affect mammals and other animals, transferring the disease in the process.

Equine encephalitis and its symptoms

The symptoms of equine encephalitis are like any other diseases which cause encephalomyelitis (a general term for inflammation of the brain and spinal cord). Easter equine encephalitis is usually a faster acting and more deadly such disease. The appearance and development of symptoms are:

  • High fever
  • Horse stops eating
  • Depression appears in the animal
  • Horse head sites in a fallen position in relation to the body
  • Eyelids and lips remain flaccid
  • Vision becomes impaired
  • Horse legs become set far apart from each other
  • Involuntary movements begin as the brain begins to swell
  • Ataxia (poor muscle coordination)
  • Paresis (weakness in voluntary movement)
  • Paralysis

When the encephalitis has developed to a certain stage, the results are fatal. A horse dying from EEE will lie down, convulse and die.

Diagnosis of eastern equine encephalitis

After observing the symptoms of a horse affected by this virus, a veterinarian should consider different types of infection which affect the central nervous system. To determine if this is specifically an equine encephalitis virus, viral isolation is needed. This requires looking at the variety of cell linings.

Samples are often collected directly from the spinal fluid via a lumbar puncture (sometimes known as a spinal tap). Samples of nerve tissue can also be collected if the animal has already died. Testing a dead animal is important if there is a risk of an equine encephalitis outbreak and prevention methods need to be activated. ELISA tests or RNA amplification by PCR are rapid diagnostic methods commonly used in many laboratories.

Eastern Equine Encephalitis - Symptoms, Treatment and Prevention - Diagnosis of eastern equine encephalitis

Equine encephalitis treatment

There is no specific equine encephalitis treatment. Antibiotics are not effective against viruses and there is no known drug that acts as an antiviral for this disease. In severe cases, palliative and supportive treatment is used. This may include such actions as hospitalization of the horse, respiratory assistance, fluid therapy and prevention of secondary infections.

Equine encephalitis and its vaccine

Since eastern equine encephalitis is untreatable, prevention is the most important in the fight against this disease. Prevention of EEE infection can be found in the following actions:

  • Systematic vaccination: vaccinating all horses with vaccines using the attenuated virus or others with the inactive virus can help prevent equine encephalitis. In the case of any doubts, you should consult a specialized veterinarian who can make an action plan for horse vaccinations. There are two vaccines for human use which can be found on the market.
  • Control of mosquitoes: mosquitoes are a pest which can affect different areas of any country in different ways. Large culling by the use of fumigation is not recommended as it can kill many other insects and arthropods which are important to the local ecology. It is best to use localized repellents.
  • Horse stables: the stables in which the horses live, however, can be fumigated. Mosquito nets and maintaining good general hygiene are also very important. Avoid stagnant water in drums, ponds or other receptacles as they can be a breeding ground for mosquitoes.

The correct use of prevention methods greatly reduces the chances of an eastern equine encephalitis epidemic. Instances of the disease are fortunately relatively rare, but there are cases of flare ups from time to time. This could be every 10 years or so, but it will depend on various environmental factors. It is yet to be determined how climate change can affect instances of the disease, but higher temperatures can increase the proliferation of certain mosquito species.

Eastern Equine Encephalitis - Symptoms, Treatment and Prevention - Equine encephalitis and its vaccine

This article is purely informative. AnimalWised does not have the authority to prescribe any veterinary treatment or create a diagnosis. We invite you to take your pet to the veterinarian if they are suffering from any condition or pain.

If you want to read similar articles to Eastern Equine Encephalitis - Symptoms, Treatment and Prevention, we recommend you visit our Viral diseases category.

  • De la Hoz, F. (2000). Venezuelan equine encephalitis. MVZ Córdoba Magazine, 5 (1), 18-22.
  • Morales, AA, & Mendez, A. (2013). Encephalitis corners: A Review. Magazine of the National Institute of Hygiene Rafael Rangel, 44 (2), 51-60.
  • Valero, N., Larreal, Y., Arias, J., Espina, LM, Maldonado, M., Melean, E., ... & Morell, P. (2004). Seroprevalence of Venezuelan Equine Encephalitis in a population of equidae in Zulia state, Venezuela, 1999-2001. Scientific Magazine, 1 (1), 0.

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