More than 400 equine cases of West Nile virus (WNV) have been confirmed nationwide this year, according to the USDA Animal and Plant Health Inspection Service (APHIS). The current total marks a 372% increase in cases compared to last year's total.
On Oct. 2, APHIS statistics revealed 411 confirmed equine WNV cases; in 2011, just 87 confirmed cases were reported nationwide. Texas, Louisiana, and Pennsylvania have reported the most cases thus far, with 62, 50, and 36, respectively. As of Oct. 2, only seven of the contiguous states remained WNV-free: Delaware, Kansas, Maine, New Hampshire, Vermont, Virginia, and West Virginia. Alaska and Hawaii have never reported any equine WNV cases.
On Oct. 4, North Dakota State Veterinarian Susan Keller, DVM, told TheHorse.com that 15 cases of equine WNV have been reported this year in that state, compared to just one in 2011, although the actual number of cases could be higher.
"Many horses are treated and not tested, and there are likely many that are not even taken to a vet or the signs are mild and the case goes unnoticed," she relayed.
"The message we are sharing is that we relearned that unvaccinated horses are at risk," Keller continued. "Vaccinate and make sure all equines are boostered as needed."
Similarly, Iowa State Veterinarian David Schmitt, DVM, reported Oct. 5 that 24 equine WNV cases had been confirmed and that he was awaiting the case reports from submitting veterinarians on four more cases.
"Certainly, there is an increase (in WNV cases) this year in Iowa; Last year we had one equine case," he said. "All of the equine WNV cases this year in Iowa either had not been vaccinated or only had received one dose of the vaccine."
Maureen Long, DVM, MS, PhD, Dipl. ACVIM, professor in the University of Florida College of Veterinary Medicine Department of Infectious Diseases and Pathology, said Oct. 8 that although there is a spike in WNV cases nationwide, Florida has seen many more human cases than equine cases.
"There are two main reasons we are not seeing as big of a spike (in Florida)," she explained. "One, there are more cases occurring but they are not being reported; and two, vaccination has decreased the morbidity (illness) of disease. I think that both factors are important."
Looking at the nationwide picture, Long relayed that the spike in equine cases isn't necessarily a surprise: "Endemic mosquito-borne diseases undergo cycles of 10-30 years and I think this is an indication of normal cycle for WNV since it is now a resident disease. Many factors account for these cycles: the reservoir host becomes more susceptible again as adult resistant birds age and die, the virus changes or mutates and causes more disease, and cyclical weather patterns. One or all of these factors may be at play here. One prediction can be made, and it's that WNV is here to stay and we will see these cyclical outbreaks."
In the mean time, Long said there are steps horse owners can take to reduce their charges' risk of contracting WNV.
"Horse owners need to keep their horses vaccinated even in years where there is little reporting of WNV to keep up protection," she relayed. "Keep barns and stable yards free of debris and standing water. Where possible get help from ... experts on ways to control mosquitoes on the farm if there is high mosquito activity."
And finally, she reminded horse owners of an important step that might go forgotten when trying to keep animals WNV-free: "People need to protect themselves!"
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.