Equine vaccinations essential during peak mosquito season

This year's wet spring provided optimal conditions for mosquito breeding, and thus a large population of mosquitoes. Late summer coincides with peak mosquito season, which brings an increased risk of mosquito-borne diseases such as West Nile Virus and Eastern Equine Encephalitis for humans, but also for horses.

"Owners are encouraged to talk to their veterinarian about having their horses vaccinated against these viruses," said Delaware State Veterinarian Dr. Heather Hirst. "It may take several weeks for a horse's immune system to mount a response to the disease after the vaccine is given, so owners should have their horses vaccinated as soon as possible."

In nature, WNV and EEE are maintained in a cycle between mosquitoes and wild birds. Mosquitoes that feed on the infected wild birds may then bite humans or horses, infecting them with the viruses. Neither disease can be transmitted between horses or from horses to people.

Last week, the Delaware Division of Public Health Laboratory reported this year's first finding of WNV in blood samples taken from DNREC's sentinel chickens that are monitored for mosquito-borne diseases. The samples are collected as part of a statewide surveillance program conducted by DNREC's Mosquito Control Section.

Delaware has not had any cases of WNV or EEE in horses, humans, or wild birds thus far in 2017. Illnesses were last seen in one Delaware horse with WNV in 2015 and two horses with EEE in 2013. However, several states south of Delaware have reported cases this year, including Virginia and South Carolina in July.

Both diseases cause severe, and sometimes fatal, infections in horses. Signs of infection in horses include fever (although not always with WNV), anorexia, head pressing, depression or personality change, wobbling or staggering, weakness, blindness, convulsions, muscle spasms in the head and neck, or hind-limb weakness. If owners notice any of these signs in their horses, they should contact their veterinarian immediately.

Horse owners can take several steps in the barn and around the farm to help protect horses from WNV and EEE. Horses should be kept inside during dawn and dusk, which are peak hours for mosquito activity. Topical insect repellents labeled for use on horses may be applied. The wind generated by fans installed in horse stalls can also help deter mosquitoes. Old tires and containers should be disposed of and standing water eliminated. Water troughs or buckets should be emptied, cleaned, and refilled every 2-3 days if possible to remove any mosquito eggs or larvae.

For more information about WNV or EEE:
• Human health questions should be directed to the Delaware Division of Public Health, 888-295-5156 or 302-744-4990.
• Animal health questions should be directed to the Poultry and Animal Health Section at the Delaware Department of Agriculture at 800-282-8685 or 302-698-4500.
• Questions about the state's mosquito control program or mosquito biology should be directed to the Delaware Department of Natural Resources and Environmental Control's Mosquito Control Section at 302-739-9917.