Increased West Nile Virus activity occurring in Delaware

An increase in mosquito-transmitted West Nile Virus activity is occurring in many areas in Delaware, as indicated in sentinel chickens used by the Delaware Department of Natural Resources and Environmental Control to monitor for certain mosquito-transmitted diseases.

A group of 20 sentinel chicken stations is sampled weekly throughout the state each summer and fall to help track West Nile Virus and Eastern Equine Encephalitis, the primary mosquito-transmitted human health threats in Delaware. Mosquito-transmitted virus occurrences in these sentinel chickens are unrelated to Delaware’s poultry industry.

To date, 40 sentinel chickens statewide have tested positive for West Nile Virus, with over half of these findings, 25, having occurred in the last few weeks. West Nile Virus has been detected from a total of 10 sentinel chicken stations, involving 32 chickens in New Castle County from six stations, four chickens in Kent County from two stations, and four chickens in Sussex County from two stations. This typically higher initial gradient of West Nile Virus detection upstate is followed in most years with increased occurrences downstate in mid-fall. Eastern Equine Encephalitis has not been found this year in the sentinel chickens.

There has been one West Nile Virus human case to date in 2021, reported Sept. 3 by the Delaware Division of Public Health. No Eastern Equine Encephalitis human cases have been reported this year.

Staff from DNREC’s Division of Fish and Wildlife humanely care for DNREC’s sentinel chickens. Blood samples collected from sentinel chickens by the DNREC Mosquito Control section are tested for evidence of West Nile Virus and Eastern Equine Encephalitis by the Delaware Public Health Laboratory.

This is the peak time of year for mosquito-transmitted disease activity, which will continue well into October or beyond, until the onset of colder weather. While these recent West Nile Virus findings are not cause for excessive alarm, Delaware residents and visitors are urged to be vigilant over the coming month and weeks to avoid or reduce exposure to mosquito bites.

Common-sense precautions when outdoors in mosquito-prone areas include wearing long-sleeved shirts and long pants, applying insect repellent containing 10 to 30 percent diethyl toluamide or other EPA-approved insect repellents in accordance with label instructions, and avoiding mosquito-infested areas and times of peak mosquito activity around dusk, dawn and at night.

More measures can be taken by property owners to reduce mosquito-breeding habitat and mosquito populations and the chances for disease transmission. DNREC’s Mosquito Control section recommends draining or removing outdoor items that collect water, a lengthy list that includes discarded buckets or containers, uncovered trashcans, stagnant birdbaths, uncovered rain barrels or cisterns, old tires, upright wheelbarrows, flowerpot liners and saucers, depressions in boat tarps, clogged rain gutters, corrugated downspout extenders and unused swimming pools. All these items from the home landscape can become mosquito habitat very quickly and abet West Nile Virus activity.

Both West Nile Virus and Eastern Equine Encephalitis can adversely affect people and horses, and there are no human vaccines for either disease. About 80 percent of people infected with West Nile Virus show no symptoms, while about 20 percent of those infected will develop mild symptoms such as low fever, headache, body aches, a skin rash on chest or back, and swollen lymph glands. Only about one in 150 people infected with West Nile Virus might develop severe infection indicted by high fever, disorientation, tremors or convulsions, encephalitis or meningitis, all possibly leading to hospitalization and very rarely, death. Some survivors of severe cases of West Nile Virus can have long-lasting medical complications including lingering paralysis. Eastern Equine Encephalitis can be a more severe disease than West Nile Virus, typically with more serious symptoms and a human fatality rate greater than 30 percent, though EEE is much rarer than West Nile.

The mosquito control section has increased mosquito population surveillance efforts in the vicinity of virus-positive findings and initiated targeted mosquito control actions as warranted, based on biting mosquito species and the numbers of them encountered.

To request mosquito relief in downstate areas south of Dover, contact DNREC Mosquito Control’s Milford field office at 302-422-1512. To report suspected cases of human West Nile Virus, call the Division of Public Health Office of Infectious Disease Epidemiology toll-free at 888-295-5156.

For more information on West Nile Virus or Eastern Equine Encephalitis, go to cdc.gov.