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West Nile virus: Why majority of infected people don’t even know but others get very ill

By Carolyn Sistrand, AccuWeather staff writer

Hot weather this summer has increased mosquito activity in many parts of the country. More mosquitoes typically means more itchy bites, and it also means more reported cases of the West Nile virus.

The West Nile virus is an arthropod-borne virus (arboviral) disease transmitted through birds and mosquitoes. Typically, a mosquito will become infected after coming into contact with an infected bird. Humans can, then, get infected through a mosquito bite by an infected mosquito.

Mosquito on skin

(Photo/auimeesri/Getty Images)

“The trend that we see with West Nile virus is that we tend to see more cases in drought conditions rather than rainy conditions and a lot of that has to do with the places where mosquitoes live,” said Dr. Janet McAllister, research entomologist at The Center for Disease Control (CDC).

What is not commonly known are the two categories of arboviral viruses, like West Nile, that a person can contract: non-neuroinvasive and neuroinvasive.

The CDC says that most people do not develop any symptoms and that many who become infected with the West Nile virus don’t even realize they have it.

Meanwhile, others can experience the symptoms of non-neuroinvasive West Nile virus or “West Nile fever,” an acute systemic febrile illness.

However, those who develop more serious symptoms from West Nile may be at risk of a neuroinvasive arboviral disease.

McAllister said that this year’s number of cases is below the average so far; however, as the summer winds down, the CDC experts to see the number of reported cases increase.

As of Aug. 21, 2018, the CDC reports among 35 states there have been 231 cases of both non-neuroinvasive and neuroinvasive West Nile viruses, with eight cases resulting in death.

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“A non-neuroinvasive virus is not affecting that central nervous system,” said McAllister.

While many who contract the West Nile virus may not show symptoms, it is important to remain aware of the possible symptoms that can arise after receiving a mosquito bite.

The CDC lists symptoms of a non-neuroinvasive West Nile virus, and they often include headaches, body aches, joint pains, vomiting, diarrhea or rash.

Symptoms begin to show within days of receiving a bite.

“There is really no treatment other than trying to make them feel better,” said McAllister, who still urges those experiencing any symptoms after receiving a bite to seek medical attention.


“About 1 in 150 people who get West Nile virus will show this severe neuroinvasive disease,” said McAllister.

Neuroinvasive arboviral diseases, like West Nile, tend to have symptoms that are more severe, including an altered mental state, stiffness in the neck and weak limbs, high fever, muscle weakness and tremors.

Older individuals and people who have preexisting medical conditions can find themselves more at risk of contracting the neuroinvasive West Nile virus; however, anyone at any age could develop it.

“What is meant by neuroinvasive is that they're an infection of the brain. Those tend to be much more severe in their symptoms,” said McAllister. “It is really affecting that central nervous system.”

How to stay protected

“Keeping yourself healthy is certainly going to strengthen your immune system, but we still really don’t understand what makes some people really sick,” said McAllister. “What the CDC recommends is protecting yourself from mosquito bites.”

To protect yourself and others from mosquito bites, the CDC recommends wearing insect repellent, avoiding polluted water, keeping the air conditioning on and screening and closing windows and doors.

Also in areas that may be experiencing droughts, remain vigilant of the conditions and be aware of your risks due to increased mosquito activity.

“If your community has a mosquito control program, support that,” said McAllister. “It takes just one mosquito bite.”

For more safety and preparedness tips, visit

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