Dr. Pastula noted that summer is the time human cases start to mount – typically from July and August to the first hard freeze.
“We have been warning people here up and down the Front Range of Colorado to take prevention very seriously,” Dr. Pastula said.
He pointed out that 80% who are infected with West Nile will have no symptoms.
About 20% will have flu-like illness – high fever, body and joint aches, rash, diarrhea, or headaches. Symptoms may last for weeks. About 1% of the time, he said, people can get neuroinvasive West Nile.
Dr. Pastula explained that the virus can infect the covering of the brain and spinal cord causing meningitis with very high fever, severe headaches, stiff neck, and sensitivity to light.
So far this year, there have been 89 neuroinvasive cases reported nationally, according to the CDC.
With West Nile encephalitis, the virus “can infect the brain itself causing altered mental status, movement disorders, or weakness,” Dr. Pastula said.
Sometimes it can infect the gray matter of the spinal cord causing a West Nile virus poliomyelitis, which brings polio-like symptoms.
“The West Nile encephalitis and poliomyelitis can cause permanent deficits or even death,” he said. “It’s uncommon but it’s not trivial.”
Several vaccine candidates are in development, Dr. Pastula said, but none has reached clinical trials. Part of the reason for that, he said, is that scientists must be able to predict the timing of an outbreak.
“We’re not really great at predicting outbreaks,” he said.
Although the risk for neuroinvasive disease is small, it can be higher in certain groups, he said – those who are over age 60 years or are immunocompromised; those who have diabetes, cancer, or kidney disease; or those who have undergone organ transplants.
Those infected should see a health care professional and may be able to get relief with the usual medications for flu-like illness.
Some with severe infection may need to go to the hospital, Dr. Pastula said.
A version of this article first appeared on Medscape.com.