DOVER (Aug. 30, 2024) – The Delaware Public Health Laboratory has identified this year’s first human case of West Nile Virus (WNV) in a New Castle County resident. The individual who contracted WNV was hospitalized due to infection from the mosquito-borne illness but is recovering.

Additionally, the Office of the State Veterinarian within the Delaware Department of Agriculture has confirmed the first two cases of WNV in Delaware horses this year. The onset of symptoms in the equine cases occurred between Aug. 20 and 23. Both cases involve horses in Kent County that were not vaccinated, a 5-year-old Friesian stallion that has recovered, and a 1-year-old Quarter Horse gelding currently recovering.

WNV and Eastern Equine Encephalitis (EEE) are diseases transmitted via mosquito bites, generally in summer and fall, with a peak period for disease transmissions from mid-August to mid-October.

For humans, WNV can cause serious health problems, and the elderly and those with weakened immune systems are most at risk. 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 in rare cases, death. Anyone who experiences any of these severe symptoms should seek medical help immediately.

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. Humans can also be infected with EEE, but transmission requires a mosquito bite, and the virus cannot be directly transmitted between horses or between horses and people.

The public is reminded to take precautions to avoid mosquito bites, including wearing light-colored clothing such as 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 times of peak mosquito activity around dusk, dawn, and night. Delaware residents and landowners should also eliminate unneeded standing water on their property that might exist for four or more consecutive days, which can act as a mosquito breeding habitat.

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.

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 to remove mosquito eggs or larvae.

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 2025 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% of cases and 30% of WNV cases.

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 regular business hours from 8 a.m. – 4:30 p.m., Monday – Friday; 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.
• For mosquito biology/ecology and control, contact the Delaware Department of Natural Resources and Environmental Control’s Mosquito Control Section at 302-739-9917.
  • For requests for mosquito relief in upstate areas from Dover to the north, contact Mosquito Control’s Glasgow field office at 302-836-2555.
  • For mosquito relief requests in downstate areas south of Dover, contact Mosquito Control’s Milford field office at 302-422-1512.

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