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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: 488170

Reported Deaths: 6602
CountyCasesDeaths
Hennepin1012851589
Ramsey43273808
Dakota36543394
Anoka33430390
Washington22183261
Stearns18786202
St. Louis14866265
Scott13381107
Wright12580116
Olmsted1184890
Sherburne877174
Carver783241
Clay694587
Rice672291
Blue Earth599635
Kandiyohi580674
Crow Wing522782
Chisago501045
Otter Tail485570
Benton449290
Winona420049
Mower410031
Douglas393768
Goodhue388069
Nobles387147
Polk344663
McLeod340550
Beltrami338751
Morrison326247
Itasca314246
Becker313942
Lyon313844
Isanti308256
Steele303011
Carlton300249
Freeborn285824
Pine282616
Nicollet261541
Todd249230
Brown247237
Le Sueur237420
Mille Lacs229047
Cass221024
Waseca210117
Meeker208134
Martin190629
Wabasha18713
Roseau180917
Hubbard160741
Houston158114
Dodge15384
Renville151640
Redwood147127
Fillmore13908
Pennington137716
Chippewa136835
Cottonwood135920
Wadena131320
Faribault124517
Aitkin119233
Watonwan11798
Sibley117610
Rock116114
Kanabec108119
Pipestone101824
Yellow Medicine97717
Murray9538
Jackson94210
Swift87818
Pope8095
Marshall78415
Stevens7468
Lake74218
Clearwater71914
Lac qui Parle68616
Wilkin67711
Koochiching62111
Big Stone5163
Lincoln5122
Grant4918
Norman4788
Unassigned44768
Mahnomen4437
Kittson40921
Red Lake3615
Traverse3105
Lake of the Woods2221
Cook1180

Iowa Coronavirus Cases

Data is updated nightly.

Cases: 336947

Reported Deaths: 5491
CountyCasesDeaths
Polk51993559
Linn19497317
Scott17149212
Black Hawk14956293
Woodbury13828214
Johnson1314875
Dubuque12444195
Dallas1021893
Pottawattamie9877146
Story963545
Warren514076
Clinton502184
Cerro Gordo500683
Webster495588
Sioux479869
Marshall464273
Des Moines427961
Muscatine425693
Buena Vista412637
Wapello4042110
Jasper387267
Plymouth368578
Lee354453
Marion341171
Jones285055
Henry279837
Bremer270255
Carroll266649
Crawford253535
Boone244030
Benton240854
Washington239247
Mahaska215746
Jackson209939
Dickinson204140
Tama202865
Kossuth198655
Delaware186140
Clay184425
Winneshiek183228
Fayette179235
Page177919
Buchanan177829
Wright174231
Hamilton173842
Cedar172723
Hardin169839
Harrison167670
Clayton160154
Butler159231
Mills148420
Floyd148141
Poweshiek148030
Cherokee146236
Lyon145541
Allamakee144148
Madison143018
Iowa140323
Hancock138030
Grundy132230
Winnebago130531
Calhoun129411
Cass129251
Jefferson128634
Appanoose123347
Louisa122444
Mitchell120540
Chickasaw119915
Union119131
Sac118718
Shelby117433
Emmet115440
Humboldt113725
Guthrie109628
Franklin109219
Palo Alto101321
Howard99522
Montgomery96936
Clarke95020
Keokuk92529
Monroe89828
Adair81529
Ida81532
Pocahontas80919
Davis76523
Monona76427
Greene73110
Lucas72121
Osceola68315
Worth6678
Unassigned6590
Taylor64112
Decatur5699
Fremont5599
Van Buren53718
Ringgold50620
Audubon4769
Wayne47121
Adams3184
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