Horse Riders' Information
Nancy Nellis, Phone (406) 685-3541 PO Box 526, Pony, MT 59747
Horse care and
copyright (c) 2005
* For a healthy horse feed your horse a well balanced diet.
* Keep your horses digestive tract healthy by de-worming on a regular
* Your horse should receive vaccinations on a regular schedule.
* Keep a close eye on your horse's feet. Poorly kept feet can lead to many
different lameness problems.
* Have a veterinarian give your horse a thorough check up at least once a
As spring approaches, mosquito season is just around the corner for most areas of the United States. In the southern regions, mosquitoes are already a pest. Mosquitoes are a potential vector for several diseases in both humans and animals. In the horse, they can be the source of infection for a number of viral diseases which can infect the brain and spinal cord. We typically refer to this type of disease as "viral encephalitis" or "sleeping sickness". Eastern Equine (EEE) and Western Equine Encephalitis (WEE) are common terms recognized by most horse owners and enthusiasts and are similar conditions to West Nile viral encephalitis.
West Nile virus (WNV) infection is an important disease of both humans and horses here in the United States. It has received a great amount of attention (and rightly so) because;
1. It is a new disease to this country
2. It is a zoonotic disease (disease of animals which can be transmitted to
3. It causes serious illness and death in both man and animals
West Nile virus infection was first reported in the West Nile river region of Uganda (Africa) in 1937.
The first case of WNV disease here in the US was diagnosed in 1999 in New York. A veterinarian at the Bronx Zoo was the first person to determine that this was a new and different type of viral encephalitis that had not previously been reported in this country.
As with other viral encephalitis diseases of horses (and people), birds act as the reservoir or amplifier host. (Birds maintain this virus in the population, some bird species are very susceptible to the effects of this virus and others are not.) The virus is spread by mosquitoes. The virus is spread when a mosquito takes a blood meal from an infected bird, then feeds on a horse. So, the transmission cycle is; bird-mosquito-horse. There are 37 different types or species of mosquitoes which can transmit this virus.
Some basics about Horse Health-
Read an article about West Nile Virus...
Fortunately, in mammals, the virus does not reach high numbers in the blood. This is very important. Because the virus numbers are low in the blood, the mosquito cannot transmit the virus from horse to horse, or from horse to human.
As with most viral encephalitis infections, most horses that are exposed to the virus will not show clinical signs of disease. If the virus does reach the brain and spinal cord and noticeable disease develops, clinical signs can include any one or a combination of the following:
• Fever, impaired vision, inability to swallow
• Incoordination or ataxia, especially of the hind limbs
• Twitching of the muzzle and lower lip
• Twitching of the neck muscles, shoulders or pectoral (chest) region
• Heightened sensitivity to stimulation, such as touching or loud noises
• Stumbling, toe dragging, leaning to one side
• Paralysis of hind quarters
• Down and unable to rise
• Coma, death
These symptoms can be observed with other neurologic diseases of horses such as rabies, EPM, botulism and other viral encephalitis conditions.
Diagnosis is made by presence of clinical signs and detection of specific antibodies present in a blood sample which is determined by laboratory analysis. There is currently no specific, anti-viral treatment for WNV. Horses are treated with good supportive and nursing care, anti-inflammatory drugs and intravenous fluids.
WNV has now been reported throughout the United States. Disease prevalence and severity is always highest when a disease is first introduced into a naïve population (a population which has never been previously exposed). It now appears we have gone through the worst of it and our horse population has acquired some immunity through natural exposure to the virus as well as immunity generated by appropriate vaccine usage. But because current disease prevalence is much lower, we should not be lulled into a false sense of security. The virus is present in our bird population and will continue to be a potential threat to our horse population. We should remain vigilant to do all we can to reduce the risk to our horses.
The best approach is prevention. There are USDA approved vaccines available for use in healthy horses as an aid in the prevention of this deadly disease. Mosquito control is also a significant factor in helping to reduce the risk to your horse.
It is very important to vaccinate your horse in an effort to prevent WNV disease. Vaccination recommendations can vary with geographic area, time of year, age of horse and other factors. Because of this, it is imperative that your local equine veterinarian be consulted regarding vaccination strategies for West Nile Virus control. As always, if you have questions about the health of your horse, talk to your local equine veterinarian. He or she is the best resource to keep your horse healthy and strong.
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