Nebraska has had more deaths from West Nile virus than any other state this year as it experiences a surge in the illness. Hardest hit is the greater Omaha area.

Four people have died in Nebraska, said Dr. Tom Safranek, state epidemiologist for Nebraska and an infectious disease specialist.

The next closest states — with two deaths each as of early September — were Iowa, South Dakota, Michigan and Tennessee.

Also this year in Nebraska, more people than usual are getting sick, and far more than normal are becoming gravely ill, Safranek said.

“It’s important to get the word out,” because the disease is preventable, he said. “It’s occurring statewide, but there’s been a dramatic shift in the east-central part of the state.”

The total number of illnesses reported to the state is about double the normal amount, Safranek said: So far, 79 illnesses have been reported in Nebraska compared to the 10-year median of about 40. About half the illnesses have led to hospitalization due to meningitis or encephalitis. Normally, about 10 percent require hospitalization in Nebraska, he said.

Douglas, Sarpy and Cass Counties have accounted for 64 of the state’s cases, according to those counties’ health directors, Adi Pour in Douglas and Sarah Schram in Sarpy/Cass. In the three counties, 35 people have developed encephalitis or meningitis and had to be hospitalized.

Pour said she was struck by how strong the disease has been this year. Eight people in Douglas County have had to go into rehabilitation after leaving the hospital.

“The message needs to go out: This can be prevented,” she said.

Schram agreed.

“Education is key,” Schram said. “The best defense against West Nile virus is protecting yourself against mosquito bites.”

The disease is spread to humans by mosquitoes that pick it up from infected birds.

The standard bite-prevention advice applies: Wear long-sleeved shirts and long pants, use bug spray and avoid being outside at dawn and dusk when infected mosquitoes are most active.

There is no vaccine for humans, but anyone who has been infected develops long-lasting immunity.

Most people who are bitten by an infected mosquito never become ill. An estimated 20 percent of infected people nationally develop West Nile fever, similar to a typical flu. In less than 1 percent of the cases, the virus penetrates the blood-brain barrier and the individual develops meningitis or encephalitis, requiring hospitalization.

That West Nile would be a problem in Nebraska isn’t surprising, because the virus has become a disease of the Great Plains since arriving in the U.S. in 1999, said Roberto Cortinas, an entomologist at the University of Nebraska-Lincoln.

The Great Plains has the necessary ingredients in spades: the right species of mosquitoes, standing water and birds that are carriers, he said.

One of the important reasons West Nile has thrived in the Great Plains is that it is home to a type of mosquito, Culex tarsalis, that is highly susceptible to the virus and likes to feed on humans, said Mike Hildreth, a zoologist at South Dakota State University.

“When (Culex tarsalis) gets infected, it tends to carry a payload that is high,” he said. Another Culex species found in this area, Culex pipiens, infects humans, but evidence suggests that it’s not as effective as Culex tarsalis, he said. Both have been found in Douglas County.

Mosquito numbers are up this year in Douglas County, Pour said. Typically by early to mid-September, Douglas County has trapped an average of 1,479 mosquitoes, she said. This year, the county’s traps have caught 4,181 mosquitoes. Among the areas with West Nile-positive mosquitoes are Heron Haven, Seymour Smith Park, Boys Town and 11th and Grace Streets.

Douglas County residents can ask county health officials to treat pools of water with larvicide. Call 402-444-7481 and press zero.

Mosquito numbers peaked on July 24 in Douglas County, Pour said.

This summer’s weather probably contributed to the spike. The Culex mosquito most likely to transmit the disease to humans thrives in drought.

Nebraska had one of its wetter springs on record, followed by its 13th-driest July in 124 years of records, according to federal weather data.

Dry weather is important because the Culex tarsalis likes to lay its eggs in still water. Drought may also force mosquitoes and birds into closer proximity in smaller pools of water, said Pour and Safranek.

“It cycles between birds and mosquitoes,” Safranek said.

Infections won’t stop until temperatures drop noticeably, according to Safranek and Pour.

“We think it’s going to pass in a couple of weeks,” Safranek said, “but right now it’s still serious.”

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Nancy Gaarder helps cover public safety and weather events as an editor on The World-Herald's breaking news desk. Follow her on Twitter @gaarder. Phone: 402-444-1102.

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