DOVER — Four people in Delaware have tested positive for West Nile Virus, the Delaware Department of Health and Social Services reported Tuesday.

The cases, three in New Castle County and one in Kent County, were reported to the Division of Public Health in middle to late August.

None of the individuals reported symptoms. Instead, the virus was found as part of blood work related to a routine medical procedure.

The virus is transmitted by mosquitoes, generally from spring to fall. Nearly 80 percent of people infected will not become ill and only a little less than 20 percent of those infected will develop West Nile fever with mild symptoms (fever, headache, body aches, a skin rash on the chest or back and swollen lymph glands).

However, one in 150 people infected will develop severe infection — West Nile encephalitis or meningitis.

Symptoms of severe West Nile virus 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.

“West Nile Virus may not cause symptoms in most people, but in others it can cause a serious illness or even be fatal,” said Dr. Karyl Rattay, director of Public Health.

“It’s easy to forget that something as simple as a mosquito bite can make someone very sick. DPH reminds people to protect themselves and their families during mosquito season, which can last until the first hard frost.”

Mosquitoes also can carry several other diseases that can make people sick, and in some cases lead to death. Some human diseases carried by mosquitoes in the United States include dengue, chikungunya, as well as several viruses that cause brain inflammation (encephalitis) such as Eastern equine encephalitis and St. Louis encephalitis.

To avoid mosquito bites and reduce the risk of infection, individuals should:

• When outside, wear shoes, long-sleeved shirts, and pants. Mosquito netting can protect one’s face and neck, and infants in carriages, strollers, and playpens. Mosquitoes are most active at dusk and during the early-morning hours.

• Mosquito repellents containing DEET can be applied to the skin, but will last only a few hours before reapplication is necessary.

Use insect repellent containing less than 50 percent DEET for adults. The current American Academy of Pediatrics and Centers for Disease Control and Prevention recommend using 10 percent to 30 percent DEET for children older than 2 months old.

The higher the strength, the longer the DEET provides protection which varies from two to five hours.

• Read labels carefully and always follow the instructions. DEET should not be used on children younger than 2 months.

• Prevent mosquitoes from entering the house by using screens and keeping windows and doorways tightly sealed.

Mosquitoes prefer shallow water and tall vegetation. Eliminate standing water in your yard by changing birdbath water weekly, regularly draining pet dishes and plant pot saucers, and checking gutters, pool covers and tarps for standing water.

Store buckets, wheelbarrows, and wading pools upside down. Keep grass mowed.

In Delaware, there were no reported human West Nile virus cases in 2014, three cases in 2013 and nine cases in 2012 with one fatality. To report suspected cases , call the DPH Office of Infectious Disease Epidemiology at (888) 295-5156.

To report high numbers of biting mosquitoes or other concerns, contact the Department of Natural Resources and Environmental Control Mosquito Control Section field offices:

• Glasgow office: (302) 836-2555, the northern half of Kent County, including Dover, and all of New Castle County and

• Milford office: (302) 422-1512, for the southern half of Kent County south of Dover, and all of Sussex County.

Staff will be available from 8 a.m. to 4 p.m. Monday through Friday. At other times, callers should leave a message giving their name, phone number, address and a brief description of their need or problem.

For more information on the Department of Natural Resources and Environmental Control’s Mosquito Control, call (302) 739-9917 or visit dnrec.delaware.gov/fw/Services/Pages/MosquitoSection.aspx.

For more information about West Nile virus in horses, contact the Delaware Department of Agriculture at (302) 698-4500 or (800) 282-8685 (Delaware only).

For more general information on West Nile, visit cdc.gov/ncidod/dvbid/westnile/index.htm or for more information about mosquito bites and other diseases they may cause, visit www.cdc.gov/Features/stopmosquitoes/index.html.