The Office of the State Veterinarian announced Delaware’s third case of West Nile virus found in horses in 2018.
The infected equine is a 10-year-old pony gelding that was purchased from a Pennsylvania livestock auction and transported to a premises in New Castle County on Aug. 27. On Aug. 30, the pony was observed to have a fever, was leaning and walking sideways. He progressed to show signs of wobbling and staggering, decreased tail tone, and facial nerve deficits. Samples were submitted to the National Veterinary Services Laboratory, which confirmed the diagnosis of West Nile on Sept. 7. The vaccination history for this pony is unknown. His condition is reported to be improving.
This is the third case of West Nile reported in Delaware horses in 2018. The first and second cases were diagnosed in August, and occurred in a 3-year-old Standardbred mare residing in Kent County with unknown vaccination status and a 2-year-old Thoroughbred mare also residing in Kent County that was not up-to-date on its West Nile vaccine. The Thoroughbred horse was euthanized due to the severity of its illness.
West Nile and Eastern Equine Encephalitis are diseases transmitted to horses via the bites of mosquitoes. Humans can also be infected with West Nile and EEE, but transmission requires a mosquito bite and the virus cannot be directly transmitted between horses, or between horses and people. Signs of infection in horses include fever (although not always with West Nile), 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. Two cases of West Nile were confirmed in Delaware horses in 2017.
The Department of Natural Resources and Environmental Control’s Mosquito Control Section has seen an increase of West Nile found in wild birds and sentinel chickens this year throughout the state. Three detections of EEE, two in Sussex and one in New Castle County, have been made in sentinel chickens in the last month. So far in Delaware in 2018, five cases of West Nile have been found in humans.
The state veterinarian urges horse owners to contact their veterinarians as soon as possible, as we are in the midst of peak mosquito season, to have horses and other equines vaccinated against West Nile and EEE. Neither disease has a specific drug treatment; EEE infections in horses are fatal in 70 to 90 percent of cases, and West Nile in 30 percent of cases.
Horse owners can take several additional steps in the barn and around the farm to help protect horses from mosquito bites. 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.