The Lake County Health Department reported Thursday that a batch of mosquitoes sampled June 23 in Highland Park has tested positive for West Nile virus, which marks "the first confirmed indicator of the disease's presence" in the county this year.

According to information released by the health department Thursday afternoon, five human cases of West Nile virus were reported in Lake County in 2015, and a total of 68 pools or batches of mosquitoes and one bird tested positive for the virus.

"This is the time of year when we begin to see mosquito pools testing positive for West Nile virus," Mark Pfister, the Health Department's interim executive director, said in a statement.

Pfister added that with the arrival of hot weather, residents should protect themselves against mosquito bites by following a system of four D's drain empty water from outdoor containers; dress with long-sleeved shirts and pants to cover skin; defend with insect repellent than contains DEET; and stay indoors at dawn and dusk.

The Health Department statement added that it maintains a West Nile virus hotline for county residents to report areas of stagnant water, which are conducive for mosquito breeding, or to obtain more information on the signs and symptoms of West Nile encephalitis.

The West Nile hotline number is 847-377-8300. Information can also be found at

According to the statement, while most people infected with West Nile virus have no symptoms of illness, some may become ill, usually three to 15 days after the bite of an infected mosquito. In some individuals, particularly the elderly, the virus can cause muscle weakness, inflammation of the brain (encephalitis), stiff neck, stupor, disorientation, tremors, convulsions, paralysis, coma or death.

The Health Department conducts a mosquito-surveillance program in Lake County that includes the setting or traps beginning in late spring and continuing into the autumn, with testing taking place weekly for West Nile virus.

The department, working with municipalities and other agencies, also tests areas of stagnant water throughout the season for the presence of mosquito larvae, specifically from the Culex mosquito, which is the primary carrier of West Nile in Illinois. In addition, the locations of dead birds are monitored to assist in the assessment of potential West Nile virus activity.

Thursday's statement added that "it is also important to remember that other mosquito species carry disease such as Zika virus, dengue and Chikungunya, in areas outside northeast Illinois. People vacationing in areas with ongoing disease transmission from mosquitoes should protect themselves from any mosquito bites."

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