2017 Summary of West Nile Virus 

Equine Cases in the United States

January 1 – December 31, 2017

This report is a descriptive summary of U.S. equine West Nile virus (WNV) cases reported to the United 

States Department of Agriculture (USDA) in 2017. The USDA Animal and Plant Health Inspection Service 

(APHIS) Veterinary Services (VS) branch collaborates with the U.S. Centers for Disease Control and 

Prevention (CDC) and State veterinary and public health officials to facilitate communication about 

arbovirus disease cases in horses and confirm equine cases in each State. CDC collects arbovirus case 

information using its ArboNET reporting system, an electronic surveillance and reporting system for

tracking and reporting arboviral activity in humans and animals. During the transmission season, VS 

disseminates the equine case information to State animal health officials for confirmation and posts the 

number of confirmed cases to the USDA West Nile virus information Web site 

(http://www.aphis.usda.gov/animal-health/equine-health). Specific case definitions are also provided 

on this site. In this document, ‘reported cases’ of WNV may include presumptive positive and confirmed 

positive cases. 

In 2017, 307 equine cases of WNV were reported from 39 States. Figure 1 shows the annual number of 

equine WNV cases reported in the United States from 2004 through 2017. Figure 2 shows the number of 

equine WNV cases in each State in 2017, and Table 1 provides the number of cases per county or parish

in those States in 2017. 

Figure 1. Reported U.S. equine cases of West Nile virus, 2004-2017

1406

1088 1086

468

179

276

125 87

627

377

141

225

377

307

0

200

400

600

800

1000

1200

1400

1600

2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

Equine Cases of WNV

Animal and Plant 

Health Inspection 

Service

Veterinary 

Services

March 2018
2017 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 2

Figure 2. Distribution of reported equine WNV cases in 2017 (307 total cases)

Table 1. Reported equine WNV cases by State and county, 2017

State County West Nile Virus

Reported Cases

Alabama Blount County 1

Chilton County 1

Clay County 1

Elmore County 1

Lamar County 1

Lee County 1

Total cases for Alabama 6

Arkansas Bradley County 1

Total cases for Arkansas 1

California Contra Costa County 1

Fresno County 1

Glenn County 2
2017 Summary of West Nile Virus Equine Cases in the United States

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State County West Nile Virus

Reported Cases

Kern County 2

Lassen County 3

Los Angeles County 1

Plumas County 1

Riverside County 4

Sacramento County 1

San Diego County 1

San Joaquin County 2

Tehama County 1

Tuolumne County 1

Total cases for California 21

Colorado Boulder County 1

Larimer County 3

Lincoln County 1

Mesa County 1

Montezuma County 1

Weld County 1

Yuma 1

Total cases for Colorado 9

Connecticut Fairfield County 1

Total cases for Connecticut 1

Delaware Kent County 2

Total cases for Delaware 2

Florida Bay County 1

Collier County 1

Jackson County 1

Palm Beach County 1

Total cases for Florida 4

Georgia Brantley County 1

Carroll County 1

Coweta County 1

Elbert County 1

Gordon County 1

Laurens County 1

Pike County 1

Richmond County 1

Screven County 1

Walker County 1
2017 Summary of West Nile Virus Equine Cases in the United States

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State County West Nile Virus

Reported Cases

Worth County 1

Total cases for Georgia 11

Idaho Ada County 1

Bonner County 1

Jerome County 1

Owyhee County 1

Payette County 1

Total cases for Idaho 5

Illinois Jackson County 1

Kane County 1

McHenry County 1

Williamson County 1

Total cases for Illinois 4

Indiana Adams County 5

Elkhart County 3

Franklin County 1

Hancock County 1

Lagrange County 3

Whitley County 1

Total cases for Indiana 13

Iowa Ida County 1

Worth County 1

Total cases for Iowa 2

Kansas Reno County 1

Total cases for Kansas 1

Kentucky Adair County 2

Bourbon County 1

Franklin County 1

Garrard County 1

Graves County 1

Hardin County 1

Hart County 1

Johnson County 1

Menifee County 1

Metcalfe County 1

Pulaski County 1

Russell County 3

Total cases for Kentucky 15
2017 Summary of West Nile Virus Equine Cases in the United States

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State County West Nile Virus

Reported Cases

Louisiana Lafayette Parish 1

Morehouse Parish 1

Sabine Parish 1

St. Tammany Parish 1

Total cases for Louisiana 4

Maryland Cecil County 1

Charles County 1

Harford County 1

Total cases for Maryland 3

Michigan Clinton County 1

Delta County 1

Hillsdale County 1

Jackson County 1

Livingston County 1

Mecosta County 1

Midland County 1

Missaukee County 1

Montcalm County 1

Osceola County 1

Ottawa County 1

Roscommon County 1

St. Joseph County 1

Wexford County 2

Total cases for Michigan 15

Mississippi Itawamba County 1

Kemper County 1

Lafayette County 1

Lee County 1

Neshoba County 1

Noxubee County 1

Pontotoc County 1

Rankin County 1

Scott County 2

Winston 3

Total cases for Mississippi 13

Missouri Cedar County 1

Lincoln County 1

Morgan County 1
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State County West Nile Virus

Reported Cases

Randolph County 1

Scott County 1

Total cases for Missouri 5

Montana Cascade County 1

Golden Valley County 1

Lake County 2

Sanders County 3

Yellowstone County 1

Total cases for Montana 8

Nebraska Keith County 1

Total cases for Nebraska 1

Nevada Elko County 1

Humboldt County 1

Lyon County 4

Washoe County 2

Total cases for Nevada 8

New Jersey Gloucester County 1

Salem County 1

Total cases for New Jersey 2

New Mexico San Juan County 2

Total cases for New Mexico 2

North Carolina Columbus County 1

Vance County 1

Total cases for North Carolina 2

North Dakota Traill County 1

Total cases for North Dakota 1

Ohio Ashland County 1

Ashtabula County 1

Columbiana County 2

Holmes County 1

Licking County 1

Logan County 2

Trumbull County 1

Tuscarawas County 1

Wayne County 4

Total for Ohio 14

Oklahoma Garvin County 2

Kay County 1
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State County West Nile Virus

Reported Cases

Logan County 1

McClain County 1

Muskogee County 2

Total cases for Oklahoma 7

Oregon Harney County 5

Malheur County 1

Total cases for Oregon 6

Pennsylvania Cumberland County 2

Franklin County 3

Lancaster County 1

Mifflin County 4

Snyder County 2

Union County 1

Washington County 1

York County 1

Total cases for Pennsylvania 15

South Carolina Berkeley County 1

Charleston County 1

Cherokee County 1

Colleton County 3

Greenwood County 1

Horry County 1

Orangeburg County 1

Spartanburg County 1

Total cases for South Carolina 10

South Dakota Brule County 1

Total cases for South Dakota 1

Tennessee Cheatham County 1

Knox County 1

Monroe County 1

Total cases for Tennessee 3

Texas Bastrop County 1

Brazos County 1

Briscoe County 1

Dickens County 1

Fort Bend County 1

Gillespie County 1

Harris County 1
2017 Summary of West Nile Virus Equine Cases in the United States

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State County West Nile Virus

Reported Cases

Liberty County 1

Lubbock County 1

Palo Pinto County 1

Parker County 1

Randall County 5

Refugio County 1

Terry County 1

Total cases for Texas 18

Utah Beaver County 1

Box Elder County 4

Cache County 3

Carbon County 2

Davis County 1

Duchesne County 5

Juab County 1

Morgan County 1

Salt Lake County 2

Sevier County 1

Tooele County 3

Uintah County 2

Utah 7

Weber County 2

Total cases for Utah 35

Virginia Wythe County 1

Total cases for Virginia 1

Washington Benton County 1

Kittitas County 1

Lincoln County 1

Spokane County 6

Total cases for Washington 9

Wisconsin Adams County 1

Calumet County 1

Clark County 4

Dane County 1

Dodge County 1

Green Lake County 2

Jackson County 1

Jefferson County 1
2017 Summary of West Nile Virus Equine Cases in the United States

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State County West Nile Virus

Reported Cases

Langlade County 1

Monroe County 1

Oneida County 1

Outagamie County 2

Racine County 1

Sauk County 1

St. Croix County 2

Vernon County 1

Waukesha County 2

Total cases for Wisconsin 24

Wyoming Campbell County 1

Fremont County 2

Johnson County 1

Total cases for Wyoming 4

Total Reported West Nile Virus Equine Cases for the United States 307