DELAWARE — West Nile Virus (WNV) has been detected in Delaware for the first time in 2023 in a sentinel chicken, announced the Delaware Department of Natural Resources and Environmental Control on Tuesday. This initial finding was from a sentinel chicken station near Wilmington sampled on July 31 by the DNREC Mosquito Control Section, and then tested and reported virus positive by the Delaware Public Health Laboratory on Aug. 4. While there have been no reported WNV cases in humans this year in the state, Delawareans are reminded that the possibility of contracting mosquito-transmitted diseases, including WNV and eastern equine encephalitis (EEE), will continue until colder autumn temperatures arrive in mid-October or later.
Blood samples are collected by the DNREC Mosquito Control section each week from early July into October from the state’s outdoor-caged sentinel chickens that are humanely housed and handled at 20 monitoring stations statewide. The blood samples are tested for WNV and EEE antibodies by the Delaware Public Health Laboratory. Sentinel chickens bitten by mosquitoes carrying WNV or EEE develop antibodies to these diseases but are otherwise unaffected. Mosquitoes can transmit both WNV and EEE to humans and horses.
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 one confirmed case of invasive WNV in 2022, and none so far this year. EEE is not as prevalent as WNV but can present more severe symptoms in humans and horses.
The public is reminded to take common-sense 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.
According to the Delaware Department of Agriculture (DDA), there were no equine cases of WNV or EEE in 2022. The State Veterinarian urges horse owners to contact their veterinarians to vaccinate horses and other equines against WNV and EEE. Both vaccines are highly effective in minimizing disease and may be the reason why Delaware had no equine cases in 2022. Horses 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.
Spraying to reduce mosquito populations in areas where WNV or EEE is detected may be initiated by the DNREC Mosquito Control Section as warranted, based on factors to include mosquito population levels and mosquito species present in affected areas. To reduce mosquito-breeding habitat and chances of disease transmission, residents should drain or remove outdoor items that collect water, such as discarded buckets or containers, uncovered trashcans, stagnant birdbaths, unprotected rain barrels or cisterns, old tires, upright wheelbarrows, flowerpot liners, depressions in boat tarps, clogged rain gutters, corrugated downspout extenders, and unused swimming pools.
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 at dawn and dusk, peak hours for mosquito activity. Topical insect repellents labeled for use on horses may be applied. Wind generated by fans installed in horse stalls can also help deter mosquitoes. Water troughs or buckets should be emptied, cleaned, and refilled every 2-3 days to remove mosquito eggs or larvae.
- For mosquito biology/ecology and control, contact the DNREC Mosquito Control section office in Dover at 302-739-9917.
- For requests for mosquito relief in upstate areas from Dover north, contact Mosquito Control’s Glasgow field office at 302-836-2555.
- For requests for mosquito relief in downstate areas south of Dover, contact Mosquito Control’s Milford field office at 302-422-1512.
- For animal health questions, contact the Delaware Department of Agriculture’s Poultry and Animal Health Section at 302-698-4500.
- To report suspected cases of human WNV, call the Delaware Division of Public Health Office of Infectious Disease Epidemiology toll-free at 888-295-5156.