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Frequently Asked Questions
About West Nile Virus in Horses
Q. Why should I worry about West Nile virus?

A. West Nile virus (WNV), which is carried by mosquitoes, is a serious threat to horses. Over the past two years, more than 600 horses from 20 states were infected with the virus, and many died as a result. In New Jersey, 58 horses have been infected and 21 have died. Even though the virus affected only a small percentage of our 50,000 equids, the mortality rate of those infected in New Jersey over the past two years was 36%.

Q. Is there a vaccine for West Nile virus?

A. Yes, there is currently one vaccine available for horses, manufactured by Fort Dodge Laboratories. The overall impression of New Jersey's veterinary community is that the WNV vaccine is a safe vaccine. However, further testing must be completed to determine how well the vaccine works. The vaccine consists of a two-dose series given intramuscularly three to six weeks apart, and is available only through a licensed, accredited veterinarian. Current evidence indicates that horses should be vaccinated with both vaccine doses at least three weeks prior to mosquito exposure. If you have additional questions about the vaccine and its use, please contact your veterinarian.

Q. How might my horse get West Nile virus?

A. WNV is transmitted only when an infected mosquito bites a horse. Horses cannot get the virus from other infected animals or from each other.

Q. How can I tell if my horse is at risk for contracting West Nile virus?

A. Any horse that comes in contact with mosquitoes is at risk.

Q. How would I be able to tell if my horse was infected?

A. Infected horses may display one or more of the following symptoms:

  • Lack of coordination and stumbling (most commonly described symptom)
  • Depression or apprehension
  • Weakness of the hind limbs
  • Falling down, inability to rise
  • Muscle twitching
  • Grinding teeth
  • Colicky appearance
  • Hypersensitivity
  • Excessive sweating
  • Disorientation
  • Convulsions
  • Paralysis
Q. What should I do if I see any of these signs?

A. Call your veterinarian immediately. Prompt treatment may be life-saving!

Q. How can I protect my horse from West Nile virus?

A. You can take important actions such as:

  1. REDUCE STANDING WATER. Mosquitoes require standing water to reproduce. By eliminating, reducing or treating standing water on your property, you will help prevent the mosquito population from growing. Sources of standing water and ways to treat or eliminate them include:

    Water troughs and buckets -- Scrub troughs to remove algae and replace water at least every three days.

    Clogged gutters and drains -- Keep gutters and drains clean; use Mosquito Dunks®** or equivalent product if standing water cannot be eliminated.

    Old tires -- Remove, cut, or treat all old tires on your property - including tire jumps and those used to hold down tarps. (Your county mosquito agency can assist you with proper tire management.)

    Wash stalls and collection drains under wash stalls -- Use Mosquito Dunks® or equivalent product in collection drains if water collects and stands for more than three days.

    Any natural water including ponds, brooks and streams -- Call your county mosquito agency for an assessment. (This service is provided at no charge to county residents.)

    Drainage ditches on the farm or storm drains surrounding the farm -- Use Mosquito Dunks® or equivalent product in ditches on the farm and call your county mosquito agency regarding storm drains surrounding the property.

    Bird baths -- Empty, clean, and replace water at least every three days.

    Wading pools and plastic swimming pools -- Chlorinate pools, or clean and replace water at least every three days.

    Standing puddles on ground or in tarps -- Try to prevent water from accumulating in puddles. If this is not possible, eliminate the water by sweeping it out or otherwise removing it if it stands for longer than three days. If you cannot eliminate the water, contact your county mosquito agency for recommendations.

  2. MANAGE TURN-OUT. Mosquitoes feed at dawn and dusk, so turn-out should be arranged to have horses inside at these times, if possible. This scheduling is especially critical from mid-August until the first killing frost (in 2001 this was late November), the period when horses are most likely to be infected.

  3. MAINTAIN IMMUNE SYSTEM. Keep your horse's health maintained as recommended by your veterinarian (including vaccines, parasite control and nutrition) to optimize immune function. A weakened immune system may leave your horse more susceptible to infection from the West Nile virus.

** Mosquito Dunks® are small pellets containing Bacillus Thuringiensis israelensis (BTI), which are designed to be placed in water. They kill mosquito larvae for about 30 days and may be purchased in home improvement stores. Be sure to follow directions on the label.

For more information on WNV, call the New Jersey Department of Agriculture at (609) 292-3965 or visit our website at www.nj.gov/agriculture

Supported in part by a grant from CDC and NJDHSS

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