West Nile virus: An annual threat from mosquitoes

About 1 in 5 people infected experience flu-like symptoms

West Nile virus: An annual threat from mosquitoes

West Nile virus continues to pose a threat to public health wherever there are mosquitoes that carry it. And with mosquito season underway, cases of the “summertime flu” are likely to follow.

The virus is typically first detected in mid-May through mid-June. Most cases occur in July and August when temperatures are warmer and both people and mosquitoes, which transmit the virus, tend to be more active outdoors.

While West Nile virus is prevalent in many states with large mosquito populations, the South Dakota Department of Health reports the rate of incidents is highest in South Dakota, where Sanford Health is based. Since West Nile virus first emerged in South Dakota in 2001, it has infected 2,612 people and caused 46 deaths. Nationwide since 1999, West Nile virus has infected more than 51,700 people and caused more than 2,300 deaths.

‘Summertime flu’

Although most people infected with West Nile do not develop symptoms, 20%, or about 1 in 5, do experience symptoms, such as headaches, body aches, joint pains, vomiting, fever, fatigue and rash.

Sanford Health’s Clayton Van Balen, M.D., said West Nile virus can be detected about three to eight days after the onset of symptoms. He typically waits to test patients unless they are severely ill right away or if their symptoms worsen.

“I think of it like the ‘summertime flu,'” Dr. Van Balen said. “It’s kind of like the common cold — people have symptoms and then they get over it a few days later. But if your symptoms persist, I want you back to be re-evaluated.”

Dr. Van Balen suggests that people get checked out for West Nile virus if they experience an elevated temperature over 101 degrees, severe headaches that cannot be controlled by over-the-counter medicines, respiratory symptoms such as a cough lasting longer than a couple days, or are severely dehydrated and can’t maintain enough intake to drink.

More severe cases

About 1 in 150 people infected by West Nile virus develop a more serious illness called neuroinvasive disease, which infects the brain and spinal cord, such as meningitis. These symptoms include high fever, headache, neck stiffness, disorientation, tremors, muscle weakness, vision loss, numbness and paralysis, according to the Centers for Disease Control and Prevention.

Joshua Clayton, South Dakota state epidemiologist, said South Dakota has one of the highest incidents of neuroinvasive disease, which in extreme cases can be fatal.

Both the CDC and Dr. Van Balen warn that people over age 60 are at a higher risk for more severe cases of West Nile virus. Those with some other medical conditions are more prone to becoming severely ill:

  • Diabetes
  • Kidney disease
  • Hypertension
  • Cancer
  • Taking medications for conditions like psoriasis or rheumatoid arthritis


There is no specific vaccine or treatment for West Nile virus. Use over-the-counter pain medication to treat and relieve symptoms. Patients with more severe cases need to be hospitalized to receive further treatment, such as intravenous fluids.


Avoiding mosquito bites is important in preventing West Nile virus in the summer. Clayton said one way to reduce bug bites is to limit time outdoors at dusk and dawn, when mosquitoes are most active.

Dr. Van Balen suggests using age appropriate insect repellents, wearing long sleeve shirts and long pants in the mornings and at night, using screens on doors and windows and checking around home for places where mosquitoes are most likely to lay eggs, such as old tires, buckets, pools, bird baths or trash cans that may contain standing water.

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Posted In Health Information, Healthy Living