No Human Cases of WNV Reported to Date in State; Equine Owners Urged to Vaccinate Their Animals

West Nile Virus (WNV) has been detected in Delaware for the first time for 2024 in sentinel chickens that help the Department of Natural Resources and Environmental Control monitor the state for mosquito-borne illnesses, DNREC announced today. The initial WNV occurrence was found in eight sentinel chickens sampled July 22 by the DNREC Mosquito Control Section, and then tested and reported to be virus-positive by the Delaware Division of Public Health (DPH) Laboratory July 24.

The positive results came from five of the 20 sentinel chicken stations throughout the state maintained by the Mosquito Control Section – WNV-positive results came from three sentinel chicken stations in New Castle County, one in Kent County, and one in Sussex County. “Encountering eight virus-positive chickens in just one week is above the typical weekly rate for our program’s WNV findings, but perhaps reflects what seems to be an active WNV season thus far this year elsewhere in the Northeast,” said Mosquito Control Section Administrator Dr. William Meredith. While there have been no reported WNV cases yet in humans for 2024 in the state, he said, 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.

The DNREC Mosquito Control Section monitors these diseases by collecting blood samples each week starting in early July into the fall from the state’s network of outdoor-caged sentinel chickens that are humanely housed and handled. The blood samples are tested for WNV and EEE antibodies by the DPH 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.

Precautions for the public against mosquito-borne disease and illness
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 Public Health Lab reports that Delaware had four confirmed cases of neuroinvasive WNV in 2023, 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 times of peak mosquito activity around dusk, dawn and at night.

According to the Delaware Department of Agriculture (DDA), there were seven equine cases of WNV in 2023, and no EEE cases. The State Veterinarian within DDA urges horse owners to have horses and other equines vaccinated by veterinarians against WNV and EEE. While both vaccines 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.

Mosquito Control Section response to WNV and EEE
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. Residents can also contribute to lessening the chance of mosquito-borne disease transmission through eliminating mosquito habitat by draining or removing outdoor items that collect water – such as discarded buckets or containers, uncovered trashcans, stagnant birdbaths, open 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 their 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 can also 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.

More information about mosquitoes and mosquito-borne diseases is available from the following resources:

• 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 DDA Poultry and Animal Health Section at 302-698-4500.
• To report suspected cases of human WNV, call the DPH Office of Infectious Disease Epidemiology toll-free at 888-295-5156.

About DNREC
The Delaware Department of Natural Resources and Environmental Control protects and manages the state’s natural resources, protects public health, provides outdoor recreational opportunities and educates Delawareans about the environment. The DNREC Division of Fish and Wildlife, within which the Mosquito Control Section operates, conserves and manages Delaware’s fish and wildlife and their habitats, and provides fishing, hunting, wildlife viewing and boating access on more than 68,000 acres of public land owned or managed by the Division of Fish and Wildlife. For more information, visit the website and connect with @DelawareDNREC on Facebook, Instagram, X (formerly known as Twitter) or LinkedIn. 

Media Contacts:
DNREC: Michael Globetti, michael.globetti@delaware.gov; Nikki Lavoie, nikki.lavoie@delaware.gov
DDA: Stacey Hofmann, stacey.hofmann@delaware.gov
DPH: Laura Matusheski, laura.matusheski@delaware.gov

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