Most horses bitten by mosquitoes carrying the West Nile virus (WNv) do not develop clinical disease. However, up to one-third of all horses showing clinical symptoms will die. The incubation period, or the time between the bite of an infected mosquito and when clinical signs appear, ranges from 7 to 14 days. Lambton County had six equine cases in 2002 and one case in 2004 that were reported to Community Health Services Department.
The typical signs include ataxia (incoordination, stumbling, limb weakness) that either appears suddenly or appears gradually and worsens, sleepiness, dullness, listlessness, facial paralysis (droopy eyelids, lower lip), and an inability to stand. Some horses may develop mild fevers, blindness, muscle trembling, seizures and other signs.
Consult your veterinarian immediately if you observe any symptoms of WNv or other nervous system diseases in your horse. Your veterinarian will begin supportive treatment, collect samples and request laboratory tests to help identify the cause of the disease.
Horses can not spread the disease to humans, but humans are susceptible to the disease if bitten by an infected mosquito.
Protecting Your Horse from WNv
A vaccine is available as an aid in the control of WNv in horses. The initial vaccination requires two injections three to six weeks apart followed by an annual booster. A booster vaccination every six months is recommended for horses at higher risk, such as those travelling to areas of the U.S. or other countries where mosquito populations survive year-round. For full protection, vaccinations should be initiated two months prior to the start of the mosquito season.
Talk to your veterinarian about a complete vaccination program to protect your horse from the WNv and other vaccine preventable diseases.
Prevention and Control
Horse owners and rural property owners can reduce the likelihood of exposure to mosquitoes by implementing the following pest management practices:
- Keep horses stabled during peak periods of mosquito activity (dusk and dawn).
- Installing fans in barns may reduce the ability of mosquitoes to feed on horses.
- Avoid turning on lights inside barns during the evening and overnight.
- Prohibit pigeons and other birds from roosting and living in or near the stables.
- Periodically examine your property for dead birds, particularly crows and blue jays. (Report all dead bird sightings to Community Health Services Department)
- Carefully examine your property and eliminate stagnant water locations that could serve as breeding grounds for mosquitoes. Low lying areas, used tires, clogged roof gutters and manure storage areas are ideal places for mosquitoes to breed.
- Clean water troughs once a week and pay attention to puddles that form around the barn area.
- Cover rain barrels with tight-fitting fly screen.
- Do not allow water to stagnate in bird baths, wheelbarrows, ornamental ponds and swimming pools.
- Wear light-coloured long sleeved shirts, long pants and socks when outdoors.
- Use an insect repellent on yourself and your horse and apply according to label directions.
If you have any questions concerning the West Nile virus contact your local veterinarian or Community Health Services Department at 383-8331 or 1-800-667-1839. Information is also available at www.lambtonhealth.on.ca.
~Community Health Services Department of Lambton County~