Wet conditions create ideal nesting grounds for West Nile virus-carrying mosquitos and other biting, pestering insects. Given the rain, it is especially important this summer to prevent infection by keeping those mosquito populations down.

South Dakota is already in the top three states, along with North Dakota and Nebraska, for having the highest percentage annually of the more severe cases of West Nile virus in which the virus invades the brain and spinal cord, according to South Dakota State Epidemiologist Dr. Josh Clayton.

West Nile virus can be lethal.

“Last year in South Dakota we had 169 cases of West Nile virus,” Clayton said. “We had 60 hospitalizations and we did have four individuals who died from West Nile virus last year.”

Individuals at highest risk for West Nile are those 50 years or older, pregnant women, organ transplant recipients and individuals with certain medical conditions such as cancer, diabetes, high blood pressure or kidney disease.

“Those individuals can have a more severe clinical response to West Nile,” Clayton said. “It’s not a guarantee, but those are some of the factors that allow the virus to be more severe as an infection, but also to become the most severe case, which is the neuro-invasive disease, where the virus invades the brain and the spinal column.”

Of course, not all mosquitos in South Dakota carry West Nile virus, but they can still be bothersome.

Aedes Vexans (Ae. Vexans) is a floodwater mosquito that is aggressive, bites people and is seen most in the spring when there are large flooded areas, Clayton said.

Another mosquito is the Culex Tarsalis (Cx. Tarsalis). It carries West Nile virus and, though it can breed in floodwater, it can also breed in stagnant pools like those left lying around in old buckets and tires.

“That mosquito tends to bite starting (in July) around dusk and then in the early morning hours as well, and that’s when we see a lot of our West Nile virus risk,” Clayton said.

Because of the recent rain and flooding, areas that would tend to have a little bit of water and dry out fairly rapidly are going to harbor the Culex mosquito.

Though the Culex mosquito is not the most common mosquito found after a flood, an increase in its number presents a health hazard for West Nile, Clayton said.

“We do want to take seriously the fact that the additional water — all the water that we’ve seen — can contribute to more cases,” Clayton said.

The fight against the Culex mosquito generally takes two fronts: reduction of habitat and chemical warfare.

People can help to reduce Culex mosquito habitat by dumping out anything outside that can hold rainwater.

“We have a strong focus to look at the environment around your home,” Clayton said. “We recommend the ‘Tip ‘n’ Toss’ model: tipping over containers that could potentially have water in them: pet dishes, bird baths — periodically — so that you don’t have mosquitos breeding in them.”

Since the Culex mosquito is most active at dusk and at dawn, applying insect repellent at those times is an important factor in preventing a bite, but should be worn anytime you are outside near mosquito-friendly habitat.

“The Culex is most active starting around dusk through the first few hours and then potentially again in the morning just as the sun is coming up,” Clayton said. “You do want to be cautious when you are outside at those times enjoying the weather, sitting by the fire, whatever it might be.

“With that in mind, individuals should have good mosquito repellant. Repellents that contain DEET, picaridin, oil of lemon eucalyptus (p-Menthane-3,8-diol [011550]), minimizing the amount of skin that is available for the mosquito to bite. If you are wearing shorts and short sleeves, make sure you cover up with bug spray.”

The minimum percentage of DEET recommended to repel Culex for DEET products is 20 percent, which will also protect against ticks. Products with higher percentages of DEET don’t have to be reapplied as often.

Also on the chemical front, the City of Yankton is among the area communities that spray pesticide annually to kill Culex mosquito larvae in standing water before they become a threat.

This year, the Yankton Street Department has already started applying larvicide to areas of standing water in town, including the ponds on Fox Run, Transfer Station leachate ponds, storm-drain outfall areas and parts of Fantle Memorial Park.

The city also works with the state Health Department to track the Culex mosquito population with traps. Usually, Culex mosquitos begin showing up in the traps in July. When that happens, the street department plans to begin pesticide fogging in the community. Residents will be notified before that happens.

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