Dr. Damon T. Arnold, state public health director, announced the first bird testing positive for West Nile virus in Illinois this year was found in LaSalle County. "As we head into summer and temperatures get warmer, we're going to start seeing more mosquito activity and an increased risk for West Nile virus," said Dr. Arnold. "Although most cases of West Nile virus are mild, the virus can cause serious, life-altering and even fatal disease.