The West Nile disease count has hit 28 in South Dakota, an increase of six human cases from last week.

The disease has been detected in 20 counties this year.

The latest to join the list are Walworth, Kingsbury, Turner and Clark counties.

Brown County leads the state with six confirmed cases.

The West Nile virus is transmitted to humans by mosquitoes. Last year, 208 people were infected and six died in South Dakota.

People infected so far this year range in age from 15 to 78. The median age for those afflicted by the disease is 42.

Males account for nearly two-thirds of all infections in South Dakota