2016 Summary of West Nile Virus 

Equine Cases in the United States

January 1 – December 31, 2016

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 2016. 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 2016, 377 equine cases of WNV were reported from 32 States. Figure 1 shows the annual number of 

equine WNV cases reported in the United States from 2003 through 2016. Figure 2 shows the number of 

equine WNV cases in each State in 2016, and Table 1 provides the number of cases per county or parish

in those States in 2016. 

Figure 1. Reported U.S. equine cases of West Nile virus, 2003-2016

5,181

1,406

1,088 1,086

468

179 276 125 87

627

377 141 225 377

0

1,000

2,000

3,000

4,000

5,000

6,000

2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016

Equine Cases of WNV 

Animal and Plant 

Health Inspection 

Service

Veterinary 

Services

February 2017
2016 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 2

Figure 2. Distribution of reported equine WNV cases in 2016 (377 total cases)

Table 1. Reported equine WNV cases by State and county, 2016

State County

West Nile Virus

Reported Cases

Arkansas Columbia County 2

Conway County 1

Drew County 2

Faulkner County 1

Hot Spring County 1

Ouachita County 1

Perry County 1

Polk County 1

Saline County 1

Total cases for Arkansas 11

Arizona Cochise County 1

Total cases for Arizona 1

California Calaveras County 1
2016 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 3

Fresno County 2

Merced County 1

Riverside County 1

Sacramento County 3

San Diego County 1

San Joaquin County 7

Shasta County 1

Sutter County 2

Ventura County 2

Total cases for California 21

Colorado Adams County 1

La Plata County 2

Larimer County 4

Mesa County 1

Pueblo County 1

Weld County 3

Total cases for Colorado 12

Florida Osceola County 1

Total cases for Florida 1

Idaho Bonner County 2

Boundary County 2

Gooding County 1

Payette County 2

Total cases for Idaho 7

Illinois Coles County 1

Jo Daviess County 1

Mercer County 1

Moultrie County 1

Total cases for Illinois 4

Indiana Adams County 2

Clinton County 1

Elkhart County 2

Total cases for Indiana 5

Iowa Crawford County 1

Floyd County 1

Franklin County 1

Hardin County 1

Harrison County 1

Jefferson County 1

Johnson County 2
2016 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 4

Pottawattamie County 1

Sioux County 1

Van Buren County 1

Washington County 3

Webster County 1

Total cases for Iowa 15

Kansas Sedgwick County 1

Sumner County 1

Total cases for Kansas 2

Kentucky Barren County 1

Bourbon County 1

Hardin County 1

Hart County 1

Logan County 1

Powell County 1

Union County 1

Total cases for Kentucky 7

Louisiana Avoyelles Parish 1

Bossier Parish 1

Caddo Parish 2

De Soto Parish 3

Evangeline Parish 1

Iberia Parish 1

Iberville Parish 1

Ouachita Parish 1

Rapides Parish 3

St. Landry Parish 1

Tangipahoa Parish 1

Vermilion Parish 1

Webster Parish 1

Total cases for Louisiana 18

Michigan Calhoun County 1

Total cases for Michigan 1

Minnesota Becker County 1

Chisago County 1

Clearwater County 1

Goodhue County 1

Hennepin County 1

Kanabec County 2

Marshall County 1
2016 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 5

Mille Lacs County 1

Morrison County 1

Mower County 1

Olmsted County 1

Polk County 1

Renville County 1

Sibley County 1

Todd County 2

Winona County 1

Total cases for Minnesota 18

Mississippi Claiborne County 1

Hinds County 1

Kemper County 1

Lincoln County 1

Neshoba County 1

Rankin County 1

Scott County 1

Simpson County 1

Total cases for Mississippi 8

Missouri Audrain County 1

Bates County 1

Boone County 1

Johnson County 1

Pettis County 1

Vernon County 1

Webster County 1

Total cases for Missouri 7

Montana Big Horn County 1

Carbon County 2

Cascade County 1

Dawson County 1

Ravalli County 1

Valley County 1

Yellowstone County 1

Total cases for Montana 8

Nebraska Cherry County 2

Garden County 1

Saunders County 1

Seward County 1

Total cases for Nebraska 5
2016 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 6

Nevada Churchill County 2

Clark County 1

Elko County 5

Total cases for Nevada 8

North Dakota Burleigh County 1

Total cases for North Dakota 1

Ohio Pickaway County 1

Stark County 1

Tuscarawas County 4

Total for Ohio 6

Oklahoma Atoka County 4

Beckham County 1

Carter County 1

Choctaw County 1

Jackson County 1

McCurtain County 3

Muskogee County 1

Payne County 1

Sequoyah County 1

Stephens County 1

Woods County 1

Total cases for Oklahoma 16

Oregon Deschutes County 1

Klamath County 1

Malheur County 2

Umatilla County 3

Total cases for Oregon 7

Pennsylvania Centre County 2

Lancaster County 3

Mifflin County 1

Total cases for Pennsylvania 6

South Dakota Butte County 1

Total cases for South Dakota 1

Tennessee Gibson County 1

Moore County 1

Total cases for Tennessee 2

Texas Anderson County 1

Archer County 1

Austin County 3

Bastrop County 2
2016 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 7

Bowie County 5

Brazoria County 2

Brazos County 2

Burleson County 2

Burnet County 1

Caldwell County 1

Camp County 1

Cass County 2

Cherokee County 3

Coke County 1

Collin County 1

Comanche County 1

Cooke County 1

Denton County 3

Eastland County 1

Ector County 1

Erath County 4

Fayette County 2

Franklin County 2

Freestone County 3

Galveston County 1

Grayson County 1

Gregg County 1

Grimes County 4

Guadalupe County 1

Harris County 4

Harrison County 1

Hays County 1

Henderson County 2

Hopkins County 3

Houston County 1

Hunt County 2

Jasper County 2

Lamar County 1

Lavaca County 1

Lee County 1

Leon County 1

Limestone County 1

Madison County 1

McLennan County 1
2016 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 8

McMullen County 1

Montgomery County 4

Morris County 4

Nacogdoches County 3

Navarro County 1

Palo Pinto County 1

Parker County 1

Polk County 1

Randall County 1

Robertson County 2

Rockwall County 1

San Jacinto County 3

Shelby County 1

Smith County 5

Stonewall County 1

Tarrant County 2

Taylor County 1

Throckmorton County 1

Titus County 2

Tom Green County 1

Travis County 1

Trinity County 2

Upshur County 3

Van Zandt County 2

Victoria County 1

Waller County 7

Washington County 3

Wichita County 1

Williamson County 1

Wood County 1

Total cases for Texas 136

Utah Box Elder County 1

Duchesne County 2

Uintah County 3

Total cases for Utah 6

Washington Benton County 1

Franklin County 1

Grant County 1

Kittitas County 1

Lincoln County 2
2016 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 9

Okanogan County 4

Pend Oreille County 2

Spokane County 8

Stevens County 6

Yakima County 1

Total cases for Washington 27

Wisconsin Clark County 4

Jefferson County 1

Rusk County 1

St. Croix County 1

Total cases for Wisconsin 7

West Virginia Mineral County 1

Total cases for West Virginia 1

Wyoming Campbell County 1

Fremont County 1

Total cases for Wyoming 2

Total Reported West Nile Virus Equine Cases for the United States 377