DOVER, Del. (October 26, 2023) – The Office of the State Veterinarian announced Delaware has had five confirmed cases and one suspected case of West Nile Virus (WNV) recently reported in Delaware horses. These are the first Delaware cases of WNV in horses in 2023, with the cases occurring between September 9 and October 16, 2023.

All of the recent cases involve horses that were not vaccinated, including:

• 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
• > 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 (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.

Animal health professionals with formal training in diagnosing or recognizing animal diseases and pests of horses and livestock are required to report suspected or confirmed cases of WNV and EEE to the Office of the State Veterinarian within 24 hours. Examples of animal health professionals include, but are not limited to, veterinary medical professionals, diagnostic laboratorians, biomedical researchers, public health officials, animal health officials, trained technicians, zoo personnel, and wildlife personnel with such training.

WNV 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.

Most people infected with WNV 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 WNV this year.

The public is reminded to take precautions to avoid mosquito bites, including wearing light-colored clothing of long-sleeved shirts and long pants when outdoors in mosquito-prone areas; applying insect repellent containing 10 to 30% diethyltoluamide (DEET) in accordance with label instructions; and avoiding mosquito-infested areas and at times of peak mosquito activity around dusk, dawn and at night.

With the first hard freeze, 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 WNV and EEE vaccines to their annual vaccination schedule for 2024 to help protect their horses and other equines. 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, 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 should be 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, contact the DPH Office of Infectious Disease Epidemiology (OIDE) at 302-744-4990 during normal business hours from 8 a.m. – 4:30 p.m., Monday – Friday; 1-888-295-5196 outside of normal business hours; fax: 302-622-4194; or email reportdisease@delaware.gov.
• Animal health questions should be directed to the Delaware Department of Agriculture at 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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DOVER, Del. – The Office of the State Veterinarian announced today Delaware’s first and second cases of West Nile Virus (WNV) found in horses in 2018.

The first infected horse is a 3-year-old Standardbred mare residing in Kent County. The horse began showing signs of wobbling and staggering on August 19. Samples were submitted to the National Veterinary Services Laboratory, which confirmed the diagnosis of WNV on August 24. No vaccination history was available for the horse. The horse has shown slight improvement in clinical signs.

The second infected horse is a 2-year-old Thoroughbred mare also residing in Kent County. This horse was evaluated by a veterinarian on August 25 and found to have a fever, mild wobbling and staggering, droopy eyelid, difficulty controlling muscles of the mouth and throat, and depression. Cornell University Animal Health Diagnostic Center tested samples and confirmed WNV infection on August 28. This horse was not up-to-date on its WNV vaccine. The attending veterinarian has not reported any improvement in this horse’s condition.

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. 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, two cases of WNV 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 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:
• 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 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, stacey.hofmann@delaware.gov