It's time for horse owners to vaccinate their animals against Eastern equine encephalitis and West Nile virus, two diseases that together have stricken hundreds of horses in Wisconsin since 2001.
"We've had two major outbreaks of Eastern equine encephalitis in Wisconsin in recent years. Last year we had 36 cases in horses, more than any other state," says State Veterinarian Dr. Robert Ehlenfeldt of the Wisconsin Department of Agriculture, Trade and Consumer Protection. "West Nile virus case numbers are down dramatically from the first few years after the disease arrived in Wisconsin, but that's not to say there won't be an upswing. Both diseases are easily preventable with an inexpensive vaccination."
Horses require two doses of the vaccination initially, and then boosters at least annually. "We don't recommend administering the vaccinations yourself. Work with your veterinarian, so you get the best formulation for your horse and advice about additional boosters later in the season," Ehlenfeldt says.
Both WNV and EEE are caused by viruses transmitted by mosquitoes, and both may cause encephalitis, or inflammation of the brain. EEE kills about 90 percent of horses that it strikes, and WNV kills in more than a third of all equine cases. Symptoms are similar for both diseases: depression, appetite loss, drooping eyelids and lower lip, fever, weakness, twitching, paralysis or lack of coordination, aimless wandering, circling and blindness.
Neither of the viruses is contagious between horses. While humans may also be infected by both WNV and EEE, it does not pass between horses and people. Mosquitos biting warm-blooded animals is the only route of transmission.
More than 80 Wisconsin horses have died from EEE since 2001. After decades of scattered sporadic cases in Wisconsin, an outbreak in 2001 left 42 horses dead. Sporadic cases occurred most years until 2011, when 36 cases were reported. Most or all were fatal.
The first West Nile virus cases in Wisconsin horses were reported in 2002, when 156 cases were reported. The number of cases began dropping rapidly, as people started vaccinating their horses. Last year, there were just three equine cases in Wisconsin.
"The problem is that people get complacent when the numbers drop, and stop vaccinating," Ehlenfeldt said. "That, and a bumper crop of mosquitoes up north last summer, might account for the outbreak of EEE."
Besides vaccination, Ehlenfeldt recommends taking other steps to limit horses' exposure to mosquitoes:
Wisconsin Veterinary Medical Association 2801 Crossroads Drive, Suite 1200 | Madison, WI 53718 | Phone: (608) 257-3665 | Fax: (608) 257-8989
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