Increased West Nile Virus Activity Occurring in Delaware

Public Urged to Take Precautionary Measures from Biting Mosquitoes

An increase in mosquito-transmitted West Nile Virus (WNV) 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. Twenty sentinel chicken stations are sampled weekly throughout the state each summer and fall to help track WNV and Eastern Equine Encephalitis (EEE), the primary mosquito-transmitted human health threats in Delaware. Mosquito-transmitted virus occurrences in these sentinel chickens are unrelated to Delaware’s poultry industry.

A statewide total of 40 sentinel chickens have tested positive for WNV to date, with over half of these findings, 25, having occurred in the last few weeks. WNV 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 WNV detection upstate is followed in most years with increased WNV occurrences downstate in mid-fall. EEE has not been found this year in the sentinel chickens.

There has been one WNV-human case to date in 2021, reported September 3rd by the Delaware Division of Public Health. No EEE 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 WNV and EEE 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 WNV 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 exposures 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% diethyl toluamide (DEET) 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 WNV activity.

Both WNV and EEE can adversely affect people and horses, and there are no human vaccines for WNV or EEE. About 80% of people infected with WNV show no symptoms, while about 20% 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 WNV 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 WNV can have long-lasting medical complications, including lingering paralysis. EEE can be a more severe disease than WNV, typically with more serious symptoms and a human fatality rate greater than 30%, though EEE is much rarer than WNV.

In response to WNV activity as has been recently detected or future EEE occurrences, 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.

Additional information about mosquitos and mosquito-borne diseases is available from the following resources:

· For mosquito biology/ecology and control, contact the 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 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, visit www.cdc.gov/ncidod/dvbid/westnile/index.htm.

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DNREC