Delaware announces two more cases of West Nile Virus in horses

DOVER, Del. – The Office of the State Veterinarian announced today Delaware’s fourth and fifth cases of West Nile Virus (WNV) found in horses in 2018. Three previous cases of WNV in horses were reported in 2018, two in August and one in September.

The fourth case of WNV confirmed in a Delaware horse occurred in a 1-year-old Standardbred mare residing in Kent County. The horse received veterinary care for loss of control of limbs and buckling over in the front limbs which began on October 11. Clinical signs progressed to inability to rise, muscle twitching, and stupor. The horse was euthanized on October 15 due to the severity of its illness. She had not been vaccinated for WNV. New Bolton Center Clinical Pathology Laboratory reported positive WNV results on October 19.

The fifth infected horse is a 6-year-old Belgian mare residing in Kent County that was evaluated by a veterinarian for whole body stiffness, acting sore, and abnormal mentation consisting of aggression with a date of onset of October 12, 2018. Diagnostic specimens were submitted to the National Veterinary Services Laboratory, which confirmed the diagnosis on October 23. The mare had never been previously vaccinated against WNV. She was treated supportively and her condition was improving as of October 18.

West Nile Virus and Eastern Equine Encephalitis (EEE) are diseases transmitted to horses via the bites of mosquitoes. Humans can also be infected with WNV 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 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. Two cases of WNV were confirmed in Delaware horses in 2017.

The Department of Natural Resources and Environmental Control’s (DNREC) Mosquito Control Section has seen an increase of WNV found in wild birds and sentinel chickens this year throughout the state. There have been a total of eight EEE-positive sentinel chickens and WNV has been detected in 66 sentinel chickens and 37 wild birds. So far in Delaware in 2018, eight cases of WNV have been found in humans.

Even though we are nearing the end of the mosquito season, the State Veterinarian urges horse owners to contact their veterinarians as soon as possible to have horses and other equines vaccinated against WNV and EEE. Neither disease has a specific drug treatment, and EEE infections in horses are fatal in 70 to 90 percent of cases, and WNV 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.

For more information about WNV or EEE:
• To report suspected cases of human West Nile Virus, call the DPH Office of Infectious Disease Epidemiology at 888-295-5196.
• Animal health questions should be directed to the Delaware Department of Agriculture at 800-282-8685 (Delaware only) or 302-698-4500. Ask for the Poultry and Animal Health Section.
• 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.

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Media Contact: Stacey Hofmann, 302-698-4500,