West Nile virus cases rose in the US in 2018, killing 167 people

The number of West Nile virus cases rose across the United States last year, killing 167 people, according to...

Posted: Aug 9, 2019 11:15 AM

The number of West Nile virus cases rose across the United States last year, killing 167 people, according to data released Thursday by the US Centers for Disease Control and Prevention. Experts say the increase, while small, underscores the need to protect against mosquitoes during the hot summer months.

There were 2,647 cases of West Nile virus last year, the CDC said, which is 550 more cases than the year before. The virus's most severe form -- neuroinvasive disease, which can cause inflammation in the brain -- was also more common last year than in years prior, according to the agency.

"I think [the report] confirms and says again that this is a significant problem in the US, that we have a couple thousand people getting very serious neurologic infections," said Dr. Mark Mulligan, director of the division of infectious diseases and immunology at the NYU Langone School of Medicine.

The increase in cases was modest, he said, and "there have been some years within those past years that have been this high, so I think there's fluctuation year-to-year."

Still, "what the report tells us is, as in years past, West Nile virus is the most frequent cause of neuroinvasive disease."

Cases reported across the country

The new data also reveals changes in where infections are found, said Sadie Ryan, an associate professor of medical geography at the University of Florida.

"It's up a little bit," she said, "but places that previously had really large numbers have less than they did, like Arizona and California." Those are states "with historically large numbers of cases," according to the CDC.

One explanation for the geographic shifts, Ryan said, could be that previously impacted regions are better prepared to track and control mosquitoes. "In places where it first popped up, it's now part of the surveillance and control efforts, so we know when to detect it, people know to spray themselves and dump their water," she said.

"It started in New York, in the Northeast, and then over the last roughly 20 years it has spread all the way across the country," said Mulligan, the NYU professor.

Last year, there were just 278 neuroinvasive infections in all of New England and the Mid-Atlantic. Meanwhile, Illinois alone saw 126 cases, while Texas reported 108.

In states long impacted by infections, like New York, people likely have greater protective immunity against the disease, Mulligan said. Only about 1 in 150 people with West Nile virus develop serious illness, according to the CDC, meaning that many cases are asymptomatic but still protect against future infection.

"A lot of people are getting infected and have no symptoms at all," Mulligan said.

"What happens is that a population develops herd immunity," he added. "Populations as a whole become relatively immune, and so the numbers of cases, as shown [in this report], are lower in many areas."

The highest incidences of infection in 2018, for example, were in Nebraska and the Dakotas. States like those "are probably areas where, in past years, there hasn't yet been a real heavy infection, so there's a higher proportion of non-immune, susceptible individuals."

How to protect against mosquito-borne disease

For those who are affected by West Nile virus, the consequences can be severe and even deadly. People over 60 years old are at greater risk for severe symptoms, which can include high fever, paralysis and even coma.

Among those who develop serious illness affecting the central nervous system, about 10% die, and in those who survive, damage can be permanent.

West Nile is transmitted by mosquitoes, making it an arbovirus -- a type of virus transmitted by bugs. There is currently no vaccine, so controlling mosquitoes is the best way to prevent infection, said Ryan, the University of Florida professor.

"Prevention is really about protecting yourself," she said. "So long sleeves, long pants, bug spray, and thinking about when mosquitoes are out." Being outside around dusk may be nice, Ryan said, but that's when mosquitoes are most likely to bite.

The CDC also tracked other arboviruses, including the tick-borne Powassan virus, which can infect the brain and lead to death. Last year, the CDC saw its first reported case of Powassan transmitted person-to-person through a blood transfusion, and the rare disease recently killed one New York resident.

The US also saw 86 cases of La Crosse virus last year. The infection is spread by mosquitoes, according to the CDC, and can lead to inflammation of the brain, seizures and paralysis. Severe disease occurs most often in children, the agency says.

"More La Crosse virus disease cases were actually reported in the 2018 data than in any year since 2011, and it's the most common cause of neuroinvasive arboviral disease in children," said Ryan. "People who are scared about their kids getting nasty diseases should be thinking about La Crosse."

Why the CDC has been receiving more reports of the virus, though, remains unclear.

"It may be increasing," Ryan said, "or we may be improving detection of cases."

Minnesota Coronavirus Cases

Data is updated nightly.

Cases: 604509

Reported Deaths: 7638
CountyCasesDeaths
Hennepin1249671779
Ramsey52513897
Dakota46840471
Anoka42774458
Washington27428291
Stearns22557225
St. Louis18138313
Scott17551136
Wright16379149
Olmsted13399102
Sherburne1202095
Carver1067448
Clay826192
Rice8202110
Blue Earth762644
Crow Wing681795
Kandiyohi667985
Chisago619952
Otter Tail585884
Benton582998
Goodhue483874
Douglas475581
Mower470533
Winona461351
Itasca459763
Isanti440064
McLeod430661
Morrison424762
Beltrami407861
Nobles407650
Steele397816
Polk389072
Becker386755
Lyon363853
Carlton353056
Freeborn347033
Pine334923
Nicollet331245
Mille Lacs311854
Brown307840
Le Sueur297326
Cass286232
Todd285633
Meeker263443
Waseca238023
Martin235332
Roseau211221
Wabasha20793
Hubbard196641
Dodge18783
Renville182446
Redwood176539
Houston174616
Cottonwood167124
Wadena163323
Fillmore157610
Faribault154719
Chippewa154038
Pennington153820
Kanabec146828
Sibley146810
Aitkin138937
Watonwan13579
Rock128719
Jackson122712
Pipestone116726
Yellow Medicine114920
Pope11306
Murray107110
Swift106918
Koochiching95418
Stevens92411
Clearwater89016
Marshall88817
Lake83220
Wilkin83213
Lac qui Parle75622
Big Stone6044
Grant5948
Lincoln5853
Mahnomen5669
Norman5479
Kittson49022
Unassigned48193
Red Lake4017
Traverse3775
Lake of the Woods3453
Cook1720

Iowa Coronavirus Cases

Data is updated nightly.

Cases: 371101

Reported Deaths: 6053
CountyCasesDeaths
Polk58263640
Linn21221339
Scott20308248
Black Hawk16157312
Woodbury15240230
Johnson1462385
Dubuque13510211
Dallas1129199
Pottawattamie11228174
Story1071648
Warren583791
Clinton561593
Cerro Gordo554095
Sioux517574
Webster515894
Muscatine4882106
Marshall486976
Des Moines467672
Wapello4338122
Buena Vista426940
Jasper421172
Plymouth403181
Lee382356
Marion366076
Jones300957
Henry294637
Bremer288461
Carroll287152
Boone268634
Crawford268240
Benton259855
Washington257351
Dickinson249344
Mahaska232651
Jackson225242
Clay216727
Kossuth216166
Tama212071
Delaware211143
Winneshiek198735
Page194522
Buchanan194033
Cedar192423
Hardin187544
Fayette186643
Wright186040
Hamilton181951
Harrison180073
Clayton171057
Butler166335
Madison164619
Mills163824
Floyd163442
Cherokee159338
Lyon158841
Poweshiek157036
Allamakee152952
Hancock150334
Iowa149824
Winnebago144531
Cass139255
Calhoun138913
Grundy137233
Emmet135841
Jefferson133535
Shelby131837
Sac130920
Union130035
Louisa129649
Appanoose129049
Mitchell126643
Chickasaw124917
Franklin123523
Guthrie123332
Humboldt119626
Palo Alto113623
Howard105022
Montgomery103638
Clarke100924
Keokuk96732
Monroe96431
Unassigned9540
Ida91535
Adair87332
Pocahontas85822
Davis85225
Monona82931
Osceola78916
Greene78011
Lucas77923
Worth7618
Taylor66812
Fremont6269
Decatur6169
Ringgold56424
Van Buren56318
Wayne54423
Audubon53311
Adams3444
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