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Mitchell ready for West Nile fight

Each day, city employees check mosquito traps around Mitchell. The traps, located at Hitchcock Park, Munroe Park, Pioneer Park and Public Beach, are used to track the rise or fall of the local mosquito population and to identify various species of the tiny, flying pests, according to Mitchell Parks, Recreation and Forestry Director Dusty Rodiek.

"If the mosquito levels reach a certain threshold in the traps for two consecutive days, that's our trigger to go out and spray," Rodiek said.

So far this year, the numbers haven't warranted citywide spraying of an insecticide that targets mosquitoes and a handful of other flying insects, Rodiek said. But the city did some preventative spraying around Lake Mitchell before the Fourth of July and near Dry Run Creek earlier this month.

Rodiek said larvacide is placed in pools of standing water in the city to prevent mosquitoes from developing, because mosquitoes lay their eggs in water and often target pools of standing water.

In Mitchell, as in most cities and towns across South Dakota, mosquito control has become especially important since the emergence of West Nile virus.

The virus, which is spread mostly by mosquitoes that have bitten infected birds, first appeared in the United States in 1999. The virus peaked in 2003, when 9,862 cases were reported nationwide, including 1,039 cases in South Dakota, according to the U.S. Centers for Disease Control and Prevention.

In the years following the outbreak of the virus, the South Dakota Department of Health often provided grants to help communities keep their mosquito populations in check.

"We knew a lot of communities were starting from zero," said South Dakota State Epidemiologist Lon Kightlinger. "Now, most communities are pretty self-sufficient."

After 2003, the number of cases of West Nile virus fell sharply both nationwide and in South Dakota. By 2011, only 712 cases were reported nationwide and only two cases were reported in South Dakota, according to the CDC.

But in 2012, the virus roared back, with 5,674 cases reported nationwide and 203 cases reported in South Dakota.

In Davison County, there have been 79 cases of West Nile virus, but no deaths, in the past 11 years, according to Kightlinger.

As of Monday, four cases of West Nile virus had been reported this year in South Dakota, with no deaths, according to the Department of Health. Those cases were in Brookings, Buffalo, Jones and Spink counties.

According to the CDC, as of Tuesday, South Dakota is one of only 10 states to have reported human cases of West Nile virus so far this year.

Between 70 and 80 percent of people infected with the virus will never develop any symptoms, the CDC reports. Most often, those people who do experience symptoms -- about one in five of those infected -- will develop a fever along with other symptoms, including headache, body aches, joint pains, vomiting, diarrhea or rash. Most of those people will recover completely, but fatigue and weakness can last for weeks or months, the CDC says.

Less than 1 percent of people infected with the virus will develop a serious neurologic illness, such as encephalitis or meningitis. Symptoms in these cases can include headache, high fever, neck stiffness, disorientation, coma, tremors, seizures or paralysis.

About 10 percent of people who develop the most severe form of the virus will die as a result, according to the CDC.

Though anyone can be infected, the CDC warns that people older than 60, and people with certain conditions such as diabetes or kidney disease, are at the greatest risk.

The number of cases across the state will almost certainly increase as the summer goes on, Kightlinger said.

"We're going to have cases," he said."We're just on the cusp of the season."

To reduce the risk of becoming infected, people should always use mosquito repellant if they're going to be outside after dusk, Kightlinger said.

"Don't let your guard down," he said. "If your city has a mosquito control program, keep it going."

Since 1999, South Dakota has had the sixth highest number of reported cases of West Nile virus, 1,962, in the country. The reason, according to Kightlinger, is a species of mosquito known as Culex tarsalis.

"That mosquito is the best vector for West Nile in the country," he said. "It's a mosquito that thrives here."

At this point, Kightlinger is unsure whether the virus will experience a similar resurgence this year as it did last year.

"This virus has surprised us so many times," he said. "It's just really hard to say what's going to happen in the future."