PIERRE - The number of human West Nile cases in South Dakota remains at an all-time low.

The Health Department says one case in Pennington County in the past week brings the state's total of human infections for the year to 36. That compares to a low of 37 cases in 2002 and last year's total of 208.

Mosquitoes can spread the virus from sick birds to humans. The infection rate usually starts falling in September when mosquitoes become less active and birds migrate south.

The transmission season isn't officially over until a hard freeze kills mosquitoes.