08/15/2025
West Nile Virus (WNV) has been detected in Delaware for the first time for 2025 in sentinel chickens that help the Delaware DNREC monitor the state for mosquito-borne illnesses.
The DNREC Mosquito Control Section reported WNV detection at three different sentinel chicken flock locations in New Castle County that were sampled Aug. 11, with virus-positive confirmation of the chickens Aug. 13 from the Delaware Division of Public Health - DPH laboratory.
The Mosquito Control Section deploys small sentinel chicken flocks throughout the state during summer and early fall as surveillance strategy for certain mosquito-borne illnesses. Weekly blood samples taken from these chickens are tested for WNV and Eastern Equine Encephalitis (EEE) antibodies by the DPH lab. Sentinel chickens bitten by mosquitoes carrying WNV or EEE develop antibodies to these diseases but are otherwise unaffected.
A positive detect informs the Mosquito Control Section about which virus is circulating in the vicinity of the detection and is evidence that infected mosquitoes in the area have passed the virus to the sentinel chickens. DNREC then conducts further surveillance on which, and how many, mosquito species are present in the area of detection, as only certain species can transmit WNV and/or EEE to humans and horses. This surveillance will in turn determine any control measures to be taken by the Mosquito Control Section.
While there have been no reported WNV cases yet in humans for 2025 in the state, Delawareans are reminded that the possibility of contracting mosquito-transmitted diseases, including WNV and EEE, will continue until colder autumn temperatures arrive in mid-October. The DPH Disease Prevention and Control Section reports that Delaware had one probable case of neuroinvasive WNV in 2024 with no human WNV cases to date this year.
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. EEE is not as prevalent as WNV but can present more severe symptoms in humans and horses.
According to the Delaware Department of Agriculture (DDA) (DDA), there were six equine cases of WNV in 2024, and no EEE cases, with no cases of either disease to date recorded this year. The State Veterinarian’s Office within DDA urges horse owners to have all their equine animals vaccinated by veterinarians against both WNV and EEE. While vaccines for the mosquito-borne illnesses are highly effective in minimizing disease, horses and equines that have been vaccinated in the past will need an annual booster shot. Neither disease has a specific drug treatment, and infections in horses are fatal in 70% to 90% of EEE cases and 30% of WNV cases.
📷: CDC