It is monsoon season and for Tucsonans that can only mean closed roads and mosquitoes. Mosquitoes are the known vector for West Nile Disease. This year, we are seeing a particularly high rise in the West Nile disease rate. According to the CDC it is at its highest level since its first detection in 1999. The most publicized outbreak is occurring in the Dallas/ Fort Worth area, but I have now had two positive cases in my practice area. The first was an unvaccinated horse, which is really taking a great risk. The other was in a yearling. The yearling had received his two sequential weanling shots, and then had been boostered in his yearling year prior to the monsoon season. He was confirmed as positive just last week. Because he was young, his immune system may not have had enough stimulation as a weanling. His protective titer may have been low. This is a very good example of why we recommend fall and spring vaccination, and for heavily exhibited animals, we additionally recommend they receive flu and rhino vaccines quarterly. The AAEP recommends once a year, but in areas with short mild winters and long summers, like Texas and Arizona, most veterinarians recommend twice yearly.
The West Nile Virus is not passed from horse to horse or from human to horse. The only way that the horse can get the virus is from the bite of a mosquito. Most horses that contract West Nile are asymptomatic, or may have very transient fever. Unfortunately there is a small percentage that will develop neurological symptoms. Some signs are as simple as drowsiness or in coordination; other far worse signs are actual decumbency, unable to rise. If you suspect your horse may be infected, a simple blood test can be run right here at our own University of Arizona Veterinary Diagnostic Laboratory. Then you can determine a course of treatment before the disease progresses too far. Antitoxin is available and supportive care is mandatory. The mortality rate for West Nile horses that have neurological disease is pretty bad. Many horses survive but have lasting neurological impairment.
Vaccinated horses that do become sick with the West Nile Virus are usually less sick, require less intensive treatment, and get better faster, with a better outcome. Also, please try to keep your horse protected from mosquitoes by reducing the amount of standing water and spray, spray, spray.
If you have not had your horses vaccinated yet, it is not too late. Please get a West Nile booster. If your horse has never had a West Nile Vaccine, he will need two sequential shots 4-8 weeks apart. It is a good idea to have the veterinarian do a physical exam, even a brief one. Your horse may need dental work, or may have developed a heart murmur. Remember that many problems go unnoticed until they are serious and expensive to treat. Call today for your West Nile Vaccination 520-760-6200.
For more information on Clinical Signs of a a horse infected with West Nile.