After a low number of equine West Nile virus cases were reported in 2011—only 87 according to the U.S. Department of Agriculture Animal and Plant Health Inspection Service —a significantly higher number of cases in 2012 has prompted veterinarians to reiterate the importance of vaccinations and barn management.
As of Sept. 4, the U.S. Geological Survey  had reported 187 cases of West Nile in non-human animals, which they said most often refers to horses. These cases have been diagnosed in 33 states with Louisiana reporting the most cases at 26.
Kathy MacGillivray, VMD, DACVIM, at the Hagyard Equine Medical Institute (Ky.), said the biggest three things horse owners can do to prevent West Nile are: vaccinate, eliminate standing water around the barn and manipulate turnout times and conditions. But MacGillivray said it can often be difficult to adjust turnout times for horses set in their ways or around busy schedules, and adjusting turnout times might be overrated anyway; vaccinating and eliminating standing water are more important.
“The vaccine is not 100 percent effective, but hopefully the signs will be much less,” said MacGillivray. “[More important than adjusting] the turnout is decreasing the things people walk by and don’t think much of, whether it be containers or buckets or whatever that have a little bit of water in [them] that attract mosquitoes. Don’t let water just sit there.
“Mosquitoes can go anywhere, but the suggestion is that you control it a little bit better with fans and repellent,” she said, adding that the one case of West Nile to which she’s personally attended was in a Thoroughbred that was stalled all day except about an hour for work.
In addition to equine victims, this year has also seen a dramatic rise in human cases. As of Sept. 4, the Center for Disease Control and Prevention  had recorded 1,993 cases in humans, 87 of those fatal. Texas reported the highest number of cases (888) and deaths (35).
According to TheHorse.com , signs of West Nile virus include flu-like symptoms, such as loss of appetite and depression. The horse may also experience muscle and skin twitching, lethargy and muscle weakness.
The American Association of Equine Practitioners recommends all horses get vaccinated once a year, preferably in the spring to cover the entire mosquito season. However, foals, older horses and horses in areas with year-round mosquito populations should receive booster vaccinations to supplement the yearly dose. Local veterinarians can recommend the proper course of action.