With mosquito season essentially wrapped up, the latest data indicates Nebraska leads the country this season not only in human cases of West Nile virus but also in deaths and serious illnesses caused by the virus.
The latest report from the Nebraska Department of Health and Human Services indicates that Nebraska had 230 total cases of West Nile and 11 deaths as of mid-October. Of the total cases, 113 — about half — have resulted in serious neurological conditions such as meningitis or encephalitis, most requiring hospitalization. Normally, about 10 percent of cases require hospitalization, according to state health officials.
The death toll in Nebraska is the second-highest on record behind the 2003 season, when 27 deaths and 2,336 human cases were reported. The number of more serious cases this year also was the highest since the 2003 outbreak year. West Nile arrived in the United States in 1999.
The next nearest state in terms of deaths is Michigan with seven, according to the latest figures from the federal Centers for Disease Control and Prevention. Iowa reported five deaths.
Public health officials in Nebraska had warned of a surge in West Nile this year, repeatedly urging residents to take precautions against mosquito bites. Particularly hard-hit has been the greater Omaha area. Douglas, Sarpy and Cass Counties combined for 111 cases.
Dr. Tom Safranek, Nebraska’s state epidemiologist, said he believes the numbers would have been higher if health officials hadn’t issued warnings.
That part of the state has the highest population, which means more people are around to be bitten, said Peter Iwen, professor of pathology and microbiology at the University of Nebraska Medical Center and director of the Nebraska Public Health Laboratory, located at UNMC.
Most people bitten by an infected mosquito never become ill. Those who have been infected develop immunity.
An estimated 20 percent of infected people nationwide develop symptoms similar to those of the flu. Fewer than 1 percent typically develop more serious conditions resulting in meningitis or encephalitis.
The state’s report indicated that the majority of deaths — eight — occurred among people ages 71 and older. Older people often are more susceptible to severe disease.
The neurological cases made up a higher proportion of cases among those 61 and older, although such illnesses also took a toll among those in lower age brackets.
Some of those who become seriously ill will have long-term disabilities. “These exact a real cost,” Safranek said.
The eastern part of the state also tallied the highest number of mosquito pools positive for West Nile. Mosquito numbers specifically were up in Douglas County.
This summer’s weather probably contributed to the spike. The type of mosquito most likely to transmit the disease in humans thrives in drought. Nebraska had a wet spring followed by a dry July.
Cooler weather, particularly a hard frost, typically puts an end to the mosquito season, and with it transmission of West Nile. With the first hard frost of the season occurring in most areas of Nebraska, according to the state report, the risk of West Nile infection now is near zero.