First 2022 Delaware Evidence of West Nile Virus Detected in DNREC’s Sentinel Chickens

West Nile Virus (WNV) has been detected in Delaware the first time for 2022 in a sentinel chicken, the Delaware Department of Natural Resources and Environmental Control announced today. This initial finding was from a sentinel chicken station in southern New Castle County sampled by the DNREC Division of Fish and Wildlife Mosquito Control section and confirmed by the Delaware Public Health Laboratory on July 19. 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 in mid-October or later.

Blood samples are collected by the 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. 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 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 2021. With the detection of WNV in a sentinel chicken this early in the season, the state veterinarian urges horse owners to contact their veterinarians as soon as possible 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 2021. 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.

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