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The virus that causes sleeping sickness travels in a continual circuit between birds, rodents, and mosquitoes. After biting an infected bird, the mosquito, or occasionally another bloodsucking insect, will then bite and feed on the horse, thereby spreading the pathogen. Birds will reveal little or no signs and symptoms of infection or illness. In some equids, spontaneous death has occurred without revealing any physical symptoms of illness or behavioral changes. No specific treatment for the disease is available, and the mortality rate can be as high as 90%.
In freshwater hardwood swamp areas where there are marked concentrations of mosquitos, animals and humans are at increased risk of acquiring the disease. The virus is found in eastern Canada, all states east of the Mississippi River, and Arkansas, Minnesota, South Dakota, and Texas. States that appear to be over-represented in cases of mosquito-borne illness include Wisconsin, Ohio, Massachusetts, Michigan and New Hampshire. Since the mosquito population swells during hot summer months, any cases of equine encephalomyelitis will likely occur from mid-July through early fall, reaching a peak time in the middle of August.
Encephalomyelitis (unlike encephalitis, which is inflammation of solely the brain) is the inflammation of both the brain and spinal cord. There are three strains of the sleeping sickness virus: Eastern equine encephalomyelitis (EEEV), Western equine encephalomyelitis (WEEV) and Venezuelan equine encephalomyelitis (VEEV). The first major outbreak of EEEV occurred along the Mid-Atlantic coast in 1933, with horses in Maryland, Delaware, Virginia and New Jersey being the most predominantly attacked. In 1934, mosquitos were determined to be the likely carrier of the pathogen.
While the three types of encephalomyelitis share many symptoms, sleeping sickness is characterized by spontaneous death, rapid and severe neurologic deterioration and mortality of 50-90%. With growing incidences worldwide of devastating mosquito-borne diseases, efforts to suppress outbreaks must be multi-pronged. Horse owners must procure annual vaccinations for their animals, implement environmental safeguards to minimize proliferation of mosquitoes in pastures and barn areas, and avail all horses of proper insect repellant products such as masks and sprays. Humans are susceptible to encephalomyelitis, but, like a horse, sustain the virus through the bite of an infected mosquito. Horses and humans do not transmit the illness to one another.
Equine encephalomyelitis is the veterinary term for sleeping sickness, a rare viral disease that affects the central nervous systems of the equine species, including zebras, donkeys, and horses.
Sleeping sickness is diagnostically challenging because symptoms will vary among horses, and may mirror other diseases of the CNS. A full diagnostic evaluation of your horse will be performed, including an evaluation of whether he is experiencing physical, neurological, or behavioral changes. The examination must take into account other cases of equine encephalomyelitis in the surrounding areas, as well as fluctuations in mosquito activity at present and within the previous year. Definitive diagnosis may require blood testing. Since death may precipitate symptoms and exam, the diagnosis may be performed postmortem.
There is no specific treatment that will successfully fight equine encephalomyelitis.
Treatment is primarily supportive and may comprise of a combination of IV fluids in case of food and water reluctance, corticosteroids to reduce inflammation, anticonvulsants, and other medications.
If your horse recovers, he will likely develop lifelong immunity. Veterinarians should be consulted about the need for revaccination in fully-recovered horses.
Your horse will remain on the veterinary supervised program. Ongoing management will call for provisions of veterinary-specified daily care.
Horse owners must get annual vaccinations for their animals, implement environmental safeguards to minimize proliferation of mosquitos in pastures and barn areas, and avail all horses of proper insect repellant products, such as a mask and ear and body spray.
Recovered horses likely develop lifelong immunity.
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