After you’ve built a bond with your horse, take him on a trail ride. He’ll look to you for security.

Our horses have gotten their spring vaccinations, including those for West Nile virus (WNV). For traveling horses like yours and mine, the exposure to West Nile virus is too great to not protect them. Here’s some history on the West Nile virus, an update on where we stand, the virus’ symptoms, a new vaccination protocol from the American Association of Equine Practitioners for your horse, and information on whether you should vaccinate pregnant mares.

History: West Nile virus infection is now considered to be everywhere in North America. It was first reported in the early 1960s in Egypt, Uganda, and France. Outbreaks occurred in Morocco in 1996, Italy in 1998, France in 2000, and of course the United States from 1999 to the present. Birds are the natural host. Bloodsucking insects, primarily mosquitoes are the vector or spreader of the virus. Horses and humans are a dead-end host — they don’t spread the virus. One horse with the disease cannot give it to another horse (or to you).

Symptoms: WNV causes inflammation of the brain and spinal cord. Primary symptoms are ataxia (unsteadiness), fever, and depression. Incubation in horses appears to be 3 to 15 days. Horses can get so bad that they’re unable to stand. Then they convulse and die. The death rate for horses that contract the virus is 33 percent. Forty percent of the horses that survive will have residual symptoms. Other equine diseases exhibit similar signs, so it’s very important to seek veterinary help immediately so that proper treatment can be started.

Vaccination protocol: We had a much lower incidence of WNV last year, and that was great. But risk of exposure and geographic distribution of WNV varies from year to year, with changes in distribution of insect vectors and virus reservoirs. The AAEP now recommends that all equines in North America be vaccinated against WNV, because of the unpredictable nature of these factors and the dire effects of the disease.

There are two licensed vaccines on the market. They work differently, but both work well. For maximum effectiveness, stay with the vaccine you started with. If you insist on changing vaccines, then start over with the two-dose series. The vaccines don’t interfere with each other, they simply ask the horse’s body to respond in different ways.

It’s best to vaccinate in the spring prior to mosquito season. Unvaccinated horses should get two doses three to six weeks apart, then annual boosters. Giving a booster every four to six months is recommended in high endemic areas. Southeast areas, where there’s a very long mosquito season, may require semiannual boosters.

Vaccinating pregnant mares: Some very serious scare tactics have been perpetrated on the horse-owning population: rumors abound that giving the WNV vaccine to pregnant mares causes birth defects. These accusations cannot be substantiated and can be ignored. Even though neither of the licensed vaccines is labeled for use in pregnant mares at this time, thousands of pregnant mares at risk for catching the virus have been safely and effectively vaccinated. It’s best to vaccinate mares prior to breeding and again four to six weeks prior to foaling. This gives the foal three to four months of protection. Foals should be vaccinated at 3, 4, and 6 months of age, then given a booster in the spring following their birth.

I’m very hopeful that this year is another good year for the entire country in terms of West Nile virus cases. I didn’t see a single case last year, and the incidence was very low compared to the previous two years. Mosquito repellents and other mosquito-control measures work wonders. If you see a dead bird, there’s a good chance the virus is close by. Step up insect control for your horse and yourself. If your horse appears ill, call your veterinarian immediately.

Don’t forget the other “spring cleaning” procedures that help keep our horses healthy and happy. Have your veterinarian give your horse a through physical examination. This includes checking your horse’s teeth, running a fecal analysis and health panel, and performing a soundness exam. Get your farrier to come out to do your horse’s feet. Discuss your riding plans for the following months, and develop a hoof-care schedule. Then pack up, take off, and hit the trail.

Barney Fleming, DVM, vets more than 60 endurance rides per year, gives endurance clinics and workshops, and is a professional lecturer on the sport of endurance riding and other equine subjects. He and his wife, Linda, own and operate Spirit Horse Escape, a horse camp and bed-and-barn in Custer, South Dakota (www.spirithorseescape.com), and an overnight horse facility in Deming, New Mexico (www.equinedoc.com).