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.

Confirmed Cases: 94189

Reported Deaths: 2046
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Hennepin26706928
Ramsey10775319
Dakota7428125
Anoka6006133
Stearns395024
Washington373555
Scott253233
Olmsted238828
Nobles196116
Blue Earth16766
Wright16037
St. Louis155539
Carver13967
Clay137140
Rice13288
Mower13225
Sherburne113714
Kandiyohi9822
Winona87018
Lyon6784
Waseca6148
Freeborn5404
Steele5402
Benton5363
Nicollet52916
Watonwan5204
Crow Wing49418
Todd4882
Chisago4841
McLeod4782
Le Sueur4604
Otter Tail4304
Beltrami4135
Martin39410
Goodhue3609
Pine3190
Itasca31314
Polk3054
Douglas2972
Isanti2890
Becker2722
Carlton2631
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Pipestone22010
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Jackson1451
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Kanabec1198
Roseau1180
Pennington1171
Fillmore1160
Lincoln1110
Hubbard971
Stevens971
Pope920
Big Stone810
Aitkin761
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Wilkin633
Grant614
Lake580
Norman540
Lac qui Parle531
Marshall511
Mahnomen461
Red Lake441
Traverse290
Clearwater270
Lake of the Woods211
Kittson120
Cook60

Iowa Coronavirus Cases

Data is updated nightly.

Confirmed Cases: 84671

Reported Deaths: 1303
CountyConfirmedDeaths
Polk15779262
Woodbury535664
Johnson510027
Black Hawk447290
Linn3973111
Story342917
Dubuque317341
Scott297128
Dallas277138
Pottawattamie208938
Buena Vista198412
Marshall177734
Sioux15653
Wapello132857
Webster125114
Plymouth112220
Clinton111221
Muscatine110054
Crawford10775
Cerro Gordo105121
Warren9516
Jasper83332
Des Moines7748
Marion7567
Henry7305
Tama70831
Carroll6605
Lee6247
Wright5811
Dickinson5106
Boone5058
Bremer4887
Washington45611
Louisa42815
Mahaska40619
Delaware3973
Franklin34718
Floyd3423
Jackson3373
Winneshiek3306
Hamilton3223
Clay3194
Lyon3184
Benton3091
Winnebago30113
Hardin2991
Poweshiek2928
Buchanan2741
Butler2702
Jones2693
Clarke2653
Kossuth2650
Shelby2651
Emmet26110
Allamakee2596
Clayton2523
Sac2480
Cherokee2462
Chickasaw2460
Guthrie2446
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Grundy2193
Fayette2172
Harrison2143
Madison2122
Iowa2041
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Humboldt1883
Palo Alto1880
Howard1876
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Page1540
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Taylor1271
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