Three Human Cases of West Nile Virus Identified in New Castle County, Marking Delaware’s First WNV Cases of Year

by Pat Haley

The Delaware Public Health Laboratory (DPHL) has identified this year’s first human cases of West Nile Virus (WNV) in three men 50 years of age and older, all of whom reside in New Castle County.

 All three individuals who contracted WNV were hospitalized due to infection from the mosquito-borne illness. At this time, it appears that each WNV victim is likely to have contracted the disease locally, but a public health investigation is ongoing, the Delaware Division of Public Health (DPH) announced today. 

In response to the human WNV cases discovered this month, the DPH and Delaware Department of Natural Resources and Environmental Control (DNREC) will increase mosquito population surveillance efforts in the vicinity of the infected individuals’ residences. Dependent on further findings, DNREC’s Mosquito Control Section in partnership with DPH may also conduct local control operations to try and prevent further WNV human transmissions. The agencies also note that the occurrence of the state’s three human cases coincides with an increase in WNV activity in the Mosquito Control Section’s sentinel chicken monitoring program, with the uptick in infected chickens typical for this time of year.

WNV is a mosquito-borne illness that can cause serious health problems. WNV is transmitted by mosquitoes, generally in summer and fall, with a peak period for disease transmissions from mid-August to mid-October. Nearly 80 percent or four in five people infected with WNV will not become ill. While only a little less than 20 percent of those infected with the virus will develop West Nile fever with mild symptoms (fever, headache, body aches, a skin rash on the chest or back and swollen lymph glands), one in 150 people infected will develop severe infection (West Nile encephalitis or meningitis). 

Symptoms of severe WNV infection include headache, high fever, stiff neck, and/or tremors and muscle weakness. The elderly and those with weakened immune systems are most at risk. Anyone who experiences any of these severe symptoms should seek medical help immediately. Symptoms may progress to stupor, disorientation, coma, convulsions, paralysis and possibly death.  

The mosquitoes that cause WNV bite primarily from dusk (evening) to dawn (morning). However, other mosquitoes that transmit diseases such as chikungunya, dengue fever and Zika can bite during the day. Applying insect repellent for personal protection is important whenever going outdoors. Wearing light-colored, long-sleeved shirts and pants is also recommended as a deterrent against mosquito bites. DPH and the DNREC Mosquito Control Section also advise reducing outdoor activities that can cause heavy breathing or excessive perspiration, not wearing perfumes or colognes, and using mosquito repellents that may contain the ingredients DEET or Picaridin in accordance with product label instructions. Additionally, Delaware residents and landowners should eliminate an unneeded standing water on their property that might exist for four or more consecutive days and that acts as mosquito breeding habitat.

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 information on mosquito control operations in Delaware, including contact information to request residential control service for biting mosquitoes, visit

For more information on West Nile Virus, visit

For more information on what you can do to prevent West Nile Virus, visit the Centers For Disease Control and Prevention’s website,

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