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The South Dakota Department of Health has confirmed the state’s first human case of West Nile virus in 2025, involving a resident of Brookings County.
In a release issued Monday, health officials said the infected individual is recovering. The department did not disclose additional identifying information due to medical privacy laws.
Since West Nile virus was first detected in South Dakota in 2002, the state has recorded more than 2,860 human cases and 54 deaths. Officials warn that late summer and early fall are peak transmission periods.
“The rate of severe infection that includes swelling of the brain and spinal cord, known as neuroinvasive disease, is highest in South Dakota and other Midwest states,” said Dr. Joshua Clayton, state epidemiologist.
West Nile virus is primarily transmitted through bites from infected mosquitoes, especially the Culex tarsalis species, which is common in South Dakota. Symptoms can range from mild fever and headaches to severe neurological illnesses like meningitis or encephalitis. The virus can be fatal in rare cases, especially among people over 50 or those with weakened immune systems.
According to the Centers for Disease Control and Prevention, about one in five people infected with West Nile will develop a fever with other symptoms, while one in 150 will develop severe illness affecting the central nervous system.
Health officials recommend the following steps to reduce exposure:
* Use mosquito repellents containing DEET, picaridin, or oil of lemon eucalyptus.
* Wear long sleeves and pants, especially between dusk and dawn.
* Eliminate standing water around homes and yards, where mosquitoes breed.
* Maintain window and door screens to prevent mosquito entry.
Brookings County has not previously recorded a confirmed human case this early in the season, according to historical data from the state health department. Officials said they are increasing mosquito surveillance and testing across eastern South Dakota.
The state maintains an online West Nile virus dashboard, updated weekly with county-level case data and mosquito pool test results. As of the most recent update, mosquito pools in seven counties have tested positive for the virus.
The Department of Health advises South Dakotans to remain vigilant through at least mid-September, when mosquito activity typically declines.
More information is available at https://doh.sd.gov.
