South Dakota leads the nation for cases of West Nile disease, and Brown County leads the state for the mosquito-borne illness, a top state health official told attendees of the South Dakota Demography Conference on May 19 in Sioux Falls. 

"When it comes to West Nile, South Dakota is No. 1 in the country," said Lon Kightlinger, the state epidemiologist. "Every county in South Dakota has had human cases of West Nile, multiple cases."

Between 1999 and 2014, South Dakota had 2,168 cases of West Nile disease reported to the federal Centers for Disease Control. 

The Rushmore state also leads the nation for the neuroinvasive form of West Nile, which means the disease gets into the brain as encephalitis or menengitis. This dangerous form of West Nile occurs in about one out of every 150 cases. 

Between 1999 and 2014, South Dakota had 55 cases per 100,000 people of neuroinvasive West Nile disease, compared to 44.6 cases per 100,000 people in No. 2 North Dakota and zero cases in Alaska and Hawaii. The national rate was 5.5 cases per 100,000 people. 

In 2015, South Dakota had more than 1 case per 100,000 people of neuroinvasive West Nile disease, one of five states with that high rate, while four states had no cases. 

Inside the state's borders, Brown County in northeastern South Dakota claims the most West Nile cases -- 267 between 2002 and 2014. Pennington County in the Black Hills is No. 2 with 190 cases, and Minnehaha County in southeast South Dakota is No. 3 with 127 cases. Deuel County claims the lowest number of cases with 6. 

When measured per capita, Sanborn County in eastern South Dakota leads with 81.7 cases per 100,000 population during that time. Brown County comes in 7th with 55.3 cases per 100,000 people, while Pennington County ranks 56th with 14.5 cases per 100,000 people and Minnehaha County ranks lowest with fewer than 6 cases per 100,000 people. 

See Dr. Kightlinger's full PowerPoint presentation attached to this post. Slides 26-33 focus on West Nile.