Delaware reports increase in equine West Nile Virus cases

Five confirmed cases of West Nile Virus and one suspected case have been recently reported in Delaware horses, the first for 2023.

The cases occurred between Sept. 9 and Oct. 16, officials said, and all of the horses had not been vaccinated. The animals include: 

• 1-year-old Standardbred mare, Kent County, confirmed case, recovered
• 3-year-old Standardbred mare, Kent County, suspected case, recovered
• 6-year-old Standardbred mare, Kent County, confirmed case, euthanized
• Over 20-year-old Percheron mare, New Castle County, confirmed case, recovered
• 1-year-old Standardbred colt, Kent County, confirmed case, recovered
• 14-year-old Standardbred mare, Kent County, confirmed, outcome unknown.

Signs of infection in horses include fever, 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.

West Nile Virus and Eastern Equine Encephalitis are diseases transmitted to horses via the bites of mosquitoes. Humans can also be infected with West Nile Virus and Eastern Equine Encephalitis, but transmission requires a mosquito bite, and the virus cannot be directly transmitted between horses, or between horses and people. Most people infected with West Nile Virus do not develop symptoms, but about 20% can develop a mild illness, including fever, body and muscle aches, headache, nausea, vomiting and rash symptoms. A small number of people can develop serious illness involving neurological problems, paralysis and possibly death. The Division of Public Health Disease Prevention & Control Section reports that Delaware had four confirmed cases of neuroinvasive West Nile Virus this year.

With the first hard freeze, officials said, the mosquito season should come to a close; however, the state veterinarian is urging horse owners to contact their veterinarians to ensure they add the West Nile Virus and Eastern Equine Encephalitis vaccines to their annual vaccination schedule for 2024 to help protect their horses and other equines. Neither disease has a specific drug treatment. Eastern Equine Encephalitis infections in horses are fatal in 70% to 90% of cases and West Nile Virus in 30% of cases, officials said.

Horse owners can protect horses from mosquito bites by keeping them in during dawn and dusk, peak hours for mosquito activity, and using topical insect repellents. Fans in horse stalls can also help deter mosquitoes. Old tires and containers should be disposed of, and standing water should be eliminated. Water troughs or buckets should be emptied, cleaned and refilled every two to three days, if possible, to remove any mosquito eggs or larvae.