 Chief Toom says the campaign will run through the end of this year. Then, leaders will measure its effectiveness and map out a plan for the future from there. South Dakota has its first case of West Nile virus for the year. West Nile is most commonly spread by mosquito bites. Health officials say you should make sure to apply repellents, wear pants and long-sleeved shirts in the evening, and limit your time outdoors from dusk to midnight when the bugs are most active.