A sweltering heat wave is building in Northern and Southern California that is expected to peak Thursday, as triple-digit temperatures increase daily. The Los Angeles County Vector Control District has warned residents that soaring heat means increased mosquito activity and a higher risk of contracting West Nile virus.

Dengue fever vector, mosquito biting hand.Getty Images

Spokeswoman Kelly Middleton urges locals to use an insect repellent such as DEET whenever they’re outdoors and to remove all standing water.