Florida Gears Up for West Nile Virus

Seasoned with the experience of handling Eastern encephalitis (EE, formerly known as Eastern Equine Encephalitis, or EEE) and St. Louis encephalitis (SLE) outbreaks, the state of Florida is preparing a strong defensive line to protect its citizens, both horses and humans, against West Nile virus (WNV). While there is no evidence WNV has reached Florida, officials want to be prepared when and if it happens.

WNV is a type of mosquito-borne encephalitis that first appeared in the Western Hemisphere in the late summer and early fall of 1999. The disease caused illness and death in humans and horses in New York last year. Verification that the virus survived the winter came when it was found in adult mosquitoes in Queens, N.Y., during January and February of this year, and in a dead red-tailed hawk in Bronxville, N.Y., in February (see The Horse of May 2000). Because it can be carried by migratory birds, WNV might invade Florida this year.

In response to the threat, state officials held an Interagency West Nile Virus Response Planning Meeting on April 18 in Gainesville, Fla. Representatives from local and state government—as well as anyone interested in the topic of WNV—were invited. A segment of the agenda devoted to equine response considerations to WNV was presented by William Jeter, DVM, Assistant Chief, Animal Disease Control of the Florida Division of Animal Industry.

"We’re taking it very seriously," said Jeter. "We’re a few steps ahead by having an excellent working relationship with the Department of Health (DOH), which has helped us to be far ahead of most other states. West Nile has been a catalyst to form partnerships (with the Department of Health, mosquito surveillance groups, and other agencies). By pooling resources, we accomplish more than by working on our own."

Nineteen states or jurisdictions have requested and received funds from the Federal government for the fiscal year 2000 for enhanced WNV surveillance and control. The total appropriation was $2.9 million. Florida has stepped up surveillance for the disease and communication between the Centers for Disease Control and Prevention (CDC), the Department of Health, Division of Animal Industry and Division of Agricultural Environmental Sciences (both part of the Department of Agriculture and Consumer Services—DOACS), veterinarians, various laboratories, health care providers, Fish and Wildlife Conservation Commission, and the Public Health Entomology Research and Education Center.

Ralph C. Knowles, DVM, is a veterinary consultant from Vero Beach, Fla., who has worked with multiple emerging disease situations over the past 36 years. He said, "Scientists believe that eventually this West Nile virus will establish itself in some part of the United States. You have to go looking for it in the best ways you know how. If you find it early, that’s a plus. But there is no excuse for not looking."

Knowles pointed out that due to its sub-tropical setting, Florida is experienced with SLE and EE, and this will give the state the upper hand in controlling any sort of an outbreak. WNV, EE, and SLE have similar signs and means of transmission and affect multiple species. There have been outbreaks of SLE in Florida every seven to 10 years, and sporadic outbreaks of EE. Surveillance routines already are in place for such diseases, and the West Nile threat will intensify those efforts.

Knowles believes that there will be a USDA-licensed vaccine for use against this virus within eight to nine months. "Vaccines are being contemplated, and will be appropriate. Measures will be taken to assure that vaccines that will be produced are safe and efficacious."

He explained that the United States was lucky when Venezuelan equine encephalomyelitis (VEE) emerged in that the preventive vaccine was derived from donkeys in Trinidad. The vaccination was distributed, and allowed the horses to develop an immunity prior to being exposed to the virus, and thus stopped the northward spread of VEE.

"We don’t have all those good things for West Nile," he said.

In a report titled "West Nile Fever—A Re-emerging Mosquito-Borne Viral Disease of Europe," researchers in Egypt made several observations that help officials here understand how WNV might behave in the United States. According to the observations, WNV caused sporadic cases and outbreaks in humans and horses in Europe. Studies showed that environmental factors—such as heavy rains followed by floods, higher than usual temperatures, or formation of ecological niches that cause a mass hatch of mosquitoes (including human activities such as irrigation)—that enhance population densities of vector mosquitoes could increase the prevalence of West Nile. Thus, the southeast coast of the United States could lend itself to an episode of WNV.

Many states, including Florida, already have taken the initiative to intensify the use of sentinel flocks of birds (usually chickens), placed at strategic locations around the state. These birds are serum-tested so that virus can be detected before it hits the general population of humans and horses. Florida might take the sentinel concept one step further.

"Ralph (Knowles) originally had the idea of having sentinel horse herds for disease surveillance," said Jeter. Monitoring to determine the geographical "hot spots" for VEE and the needs to do area vaccination, Mexico used such sentinal herds on the Eastern Gulf Coastal plane. Knowles came up with the idea to have non-mobile herds of five to six horses placed strategically where they could be serologically tested at incremental times for activity of this emerging disease.

Ranch horses in Florida often are not transported off their property, and Jeter anticipates that ranchers will be willing to have their herds established as sentinel populations. It is possible that swine might be used as a sentinel animal for surveillance as well.

Look For The Signs

Practitioners such as Ron Stenseng, DVM, Manager of the Florida Department of Agriculture and Consumer Services, have been working to build relationships with the resident horse owners in Florida, which will benefit a WNV situation when utmost cooperation is needed. Horse owners should suspect WNV if a horse is sick or off feed with an unusual or strange wobbly gait. The horse should be evaluated by your veterinarian.

Florida officials feel that owners of jumper and event horses especially are concerned since they shuttle horses between Florida and the Northeast and experienced the WNV scare last fall. Stenseng added, "The Sunshine State Horse Council wants to work with us (DOACS), and for us to present information at their meetings." Stenseng said that the Agriculture Network broadcasts programs that reach many people in the southeast and warn of disease threats.

Lee Coffman, DVM, Director of the Division of Animal Industry, Florida DOACS, explained that it is extremely difficult for some people to grasp the socioeconomic impact of the horse industry in Florida. That industry involves 350,000 resident horses, and 28,000 to 32,000 annual imports. The Florida horse industry generates more than 72,000 jobs annually.

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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