WNV Satellite Conference: Remain Wary of Disease

The years 2002 and 2003 have been the years of the horse, as far as West Nile virus (WNV) is concerned, said Robert Restifo, MS, Public Health Entomologist Administrator and chief of Ohio's Vector-borne Disease Program, at the third annual West Nile Virus Satellite Conference, in late March. "Once WNV gets into an area, it tends to stay there," he added. "West Nile virus is here, it's here to stay, and it's going to manifest itself."

More than 400 people viewed the live conference broadcast from Columbus, Ohio, at health departments and extension services across the state, and they had the opportunity to call or fax in questions following WNV presentations. Speakers included Restifo, Richard Gary, MS, Assistant Public Health Entomologist of the Vector-borne Disease Program, Jacek Mazurek, MD, MS, E.I.S. Officer in ODH; and William Saville, DVM, PhD, Dipl. ACVIM, of The Ohio State University's Department of Veterinary Preventive Medicine.

In its North American spread, WNV continues to move not only east and west, but north and south. Nine Canadian provinces have been affected, as far west as Alberta, and 2,630 horses were affected in Mexico last year. According to Restifo, public health officials are expecting California, Washington, and Oregon to get hit hard in 2004.

Hot and dry weather conditions seem to be a key factor in intense WNV activity. However, the virus still propagated under very wet conditions in Ohio last year, but at lower levels than in previous years. Restifo concluded that the constant rain kept washing away mosquito larvae, so there were many young mosquitoes around, but not as many harboring virus.

Restifo reminded that even though preventing WNV is of utmost importance, other diseases must be kept in mind as well. "If we're not careful, other things will rise up and bite us," he said. "Eastern equine encephalitis (EEE) seems to rear its head when we have very wet conditions."

Saville has been at the forefront of the effort to prevent equine WNV in the state. "It's really important that people not get complacent about this disease, because the only way we were able to control EEE and Western equine encephalitis in horses was through persistent vaccination every year," he said. "As for equine West Nile virus cases (in Ohio) for 2003, there was a marked difference--down to 106 from 644 (in 2002)."

Another reason not to become complacent is the unpredictability of the disease's spread. "For some reason, Pennsylvania had a late surge of cases last year," said Saville. No one is absolutely certain of the outbreak's cause.

Equine WNV cases in the United States are characterized by brainstem signs or cranial nerve deficits, which can cause long-term effects on a horse. "Our educational efforts have provided an incentive for people to get these horses looked at very quickly by their vets so they'll have a better success with treating them," he said.

Prevention, Prevention, Prevention
"Prevention is the most important aspect of this disease," said Saville. Mosquito source reduction and vaccination are the two key methods. Vaccination can improve a horse's likelihood to survive if he gets infected with WNV. "We followed up on 255 horses in Ohio in 2002," said Saville. "Of those that received no vaccine, almost 30% died, and of those that received one vaccine (and became infected), 14.3% died. Of those who received two or more vaccines, 5.9% died."

Even before vaccination is the importance of source reduction of mosquitoes, by getting rid of containers that hold even minute amounts of water--they are a haven for mosquito breeding. Restifo said, "A good rule of thumb is if it can hold water for a week, you should take steps to take the water out, turn (the object) over, drill a hole in it, or throw it away. Something as small as a Coke cap in a yard could breed mosquitoes."

"The best thing to do is just walk around your farm and see what you have that will hold water," he added. "You have to think outside the box of bird baths and gutters--if you get (residents in your county) thinking about that too much, then they won't pay attention to the wading pool or the five-gallon bucket."

You might have your horses fully vaccinated for WNV, but, Saville added, "If you don't reduce the standing water, you're still putting them at risk."

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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