A Chicago resident has died from West Nile virus, marking the city's first fatality linked to the mosquito-borne disease this year, the Chicago Department of Public Health has confirmed. Additional cases have been reported elsewhere in Illinois, prompting officials to spray insecticide across numerous city neighbourhoods in an effort to curb the outbreak. Health officials attribute the rise in mosquito activity to unusually heavy rainfall this summer, which has created ample breeding conditions for the insects that transmit the virus.

Most people infected with West Nile virus experience only mild symptoms, such as fever and body aches, or none at all, though around a fifth to a quarter develop flu-like illness. In rare cases the virus can invade the nervous system, causing meningitis, encephalitis, paralysis or death, with those over 50 and people with weakened immune systems most at risk. There is no vaccine or specific treatment, so experts advise prevention through insect repellent, protective clothing and removing standing water, while urging anyone over 65 or immunocompromised who develops confusion, severe headache or a stiff neck to seek emergency care immediately. Nationally, 407 human cases have been reported in the US this year, including 285 classified as severe.