After an unusually warm winter that may have promoted the growth of adult mosquitoes, Evanston health officials are testing earlier than usual this spring for West Nile virus.

Testing typically begins around May 1, but this year the city started accepting possibly infected dead birds from residents April 16, said Carl Caneva, the city’s environmental health division manager.

Last year 34 people in the Chicago area contracted the disease, and three died, he said.

West Nile virus is transmitted when mosquitoes feed on infected birds and then bite humans, Caneva said. In about four out of five West Nile virus infections, the victim does not experience any symptoms, according to the Center for Disease Control and Prevention. When symptoms do occur, they can be as mild as a rash or as severe as a coma, paralysis, or brain damage from the disease encephalitis.

Caneva gave several recommendations for those in the Evanston area, including wearing long pants and long sleeves and keeping watch of small amounts of standing water outside, such as abandoned tires or birdbaths. He said about one cup of water is the ideal amount for mosquito colonies.

“For Northwestern students, the good thing about Lake Michigan is that the more (water) movement you have, the fewer mosquitoes you have,” Caneva said. “If there is aquatic life of any kind, they’re going to eat the mosquito eggs.”

The normal mosquito season ends around the first week of fall, but if the spring and summer are warmer than usual, he said, the virus could remain until November.

“The biggest misconception is that people seem to think that if there is no rain there won’t be mosquitoes, but that’s not true,” Caneva said. “In fact, it becomes even worse in drought conditions.”

Caneva suggested residents call the city about any birds that have died for unexplained reasons so officials can collect them and test them for the virus.

– Daniel Schlessinger