2018 Summary of West Nile Virus 

Equine Cases in the United States

January 1 – December 31, 2018

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 2018. 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 2018, 493 equine cases of WNV were reported from 42 States. Figure 1 shows the annual number of 

equine WNV cases reported in the United States from 2005 through 2018. Figure 2 shows the number of 

equine WNV cases in each State in 2018, and Table 1 provides the number of cases per county or parish

in those States in 2018. 

Figure 1. Reported U.S. equine cases of West Nile virus, 2005-2018

1,088 1,086

468

179

276

125 87

627

377

141

225

380

307

493

0

200

400

600

800

1,000

1,200

2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018

Equine Cases of WNV 

Animal and Plant 

Health Inspection 

Service

Veterinary 

Services

July 2019
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 2

Figure 2. Distribution of reported equine WNV cases in 2018 (total cases)

Table 1. Reported equine WNV cases by State and county, 2018

State County West Nile 

Virus

Reported 

Cases

Alabama Dale County 1

Macon County 1

Total cases for Alabama 2

Arkansas Franklin County 1

Madison County 1

Total cases for Arkansas 2

California Amador County 1

Kern County 1

Mercer County 2

Placer County 1
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 3

State County West Nile 

Virus

Reported 

Cases

Sacramento County 3

San Joaquin County 1

Shasta County 1

Stanislaus County 1

Total cases for 

California 11

Colorado Adams County 1

El Paso County 2

Larimer County 1

Montrose County 1

Weld County 2

Total cases for Colorado 7

Connecticut Fairfield County 1

Hartford County 1

Total cases for Connecticut 2

Delaware Kent County 4

New Castle County 1

Total cases for 

Delaware 5

Florida Bradford County 1

Gilchrist County 1

Hamilton County 1

Levy County 4

Manatee County 1

Marion County 4

Osceola County 1

Washington County 1

Total cases for Florida 14

Georgia Brooks County 1

Franklin County 1

Hart County 1

Total cases for Georgia 3

Idaho Bingham County 1

Canyon County 1

Clark County 1

Jerome County 1

Owyhee County 1
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 4

State County West Nile 

Virus

Reported 

Cases

Total cases for Idaho 5

Illinois Douglas County 5

Moultrie County 2

Piatt County 1

Pike County 1

Wayne County 2

Total cases for Illinois 11

Indiana Adams County 14

Harrison County 1

Jay County 3

Lake County 1

Madison County 1

Noble County 1

Tippecanoe County 1

Whitley County 2

Total cases for Indiana 24

Iowa Bremer County 1

Buchanan County 2

Butler County 1

Clay County 1

Clinton County 1

Howard County 1

Mahaska County 1

Marshall County 1

Mitchell County 1

Polk County 3

Poweshiek County 1

Union County 1

Van Buren County 2

Wapello County 1

Total cases for Iowa 18

Kansas Butler County 1

Leavenworth County 1

Lyon County 1

Marion County 1
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 5

State County West Nile 

Virus

Reported 

Cases

Neosho County 1

Seward County 1

Wichita County 1

Total cases for Kansas 7

Kentucky Barren County 1

Boyle County 1

Carlisle County 1

Fayette County 1

Hardin County 1

Harrison County 1

Jackson County 1

Lewis County 3

Logan County 1

Magoffin County 1

Mercer County 1

Pendleton County 1

Rockcastle County 1

Todd County 1

Woodford County 1

Total cases for 

Kentucky 17

Louisiana Ascension Parish 1

Evangeline Parish 1

Lafayette Parish 1

St. Landry Parish 2

St. Tammany Parish 1

Total cases for 

Louisiana 6

Maryland Carroll County 2

Frederick County 2

Harford County 1

Prince George 1

Washington County 1

Total cases for 

Maryland 7

Franklin County 1

Hampshire County 1
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 6

State County West Nile 

Virus

Reported 

Cases

Total cases for Massachusetts 2

Michigan Gratiot County 1

Muskegon County 1

Total cases for 

Michigan 2

Minnesota Big Stone County 1

Fillmore County 2

Meeker County 1

Pine County 1

Polk County 1

Sherburne County 1

Todd County 1

Waseca County 1

Total cases for 

Minnesota 9

Missouri Cooper County 1

Gentry County 1

Laclede County 1

Mercer County 1

Pettis County 1

Total cases for Missouri 5

Montana Beaverhead County 1

Blaine County 1

Broadwater County 2

Carbon County 1

Cascade County 14

Fergus County 4

Glacier County 1

Golden Valley County 1

Judith Basin County 1

Lake County 4

Lewis and Clark County 9

Musselshell County 2

Phillips County 1

Pondera County 1

Powder River County 1

Rosebud County 1
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 7

State County West Nile 

Virus

Reported 

Cases

Sanders County 2

Wheatland County 1

Yellowstone County 2

Total cases for 

Montana 50

Nebraska Cherry County 1

Dakota County 1

Total cases for 

Nebraska 2

New Jersey Burlington County 1

Total cases for New Jersey 1

New Mexico Bernalillo County 1

Guadalupe County 1

Total cases for New Mexico 2

New York Cattaraugus County 1

Chautauqua County 2

Chenango County 2

Erie County 1

Genesee County 1

Lewis County 1

Livingston County 3

Montgomery County 1

Ontario County 1

Orleans County 2

Oswego County 1

Steuben County 1

Suffolk County 1

Tompkins County 1

Washington County 1

Total Cases for New 

York 20

North Carolina Davie County 1

Johnston County 1

Pender County 1

Surry County 1

Yadkin County 1

Total cases for North Carolina 5
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 8

State County West Nile 

Virus

Reported 

Cases

North Dakota Emmons County 1

Mercer County 1

Williams County 2

Total cases for North Dakota 4

Ohio Ashtabula County 3

Carroll County 1

Champaign County 1

Coshocton County 2

Cuyahoga County 1

Geauga County 3

Holmes County 20

Knox County 1

Licking County 1

Lorain County 2

Medina County 2

Monroe County 1

Pickaway County 1

Seneca County 1

Stark County 1

Trumbull County 2

Tuscarawas County 1

Wayne County 5

Wyandot County 1

Total for Ohio 50

Oklahoma Bryan County 1

Ellis County 1

Garvin County 1

Grady County 1

Logan County 1

Osage County 1

Payne County 1

Stephens County 1

Wagoner County 1

Woodward County 2

Total cases for 

Oklahoma 11
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 9

State County West Nile 

Virus

Reported 

Cases

Oregon Klamath County 2

Total cases for Oregon 2

Pennsylvania Adams County 2

Bedford County 1

Berks County 1

Blair County 2

Bucks County 2

Centre County 11

Chester County 9

Clearfield County 1

Clinton County 6

Columbia County 2

Crawford County 1

Cumberland County 3

Dauphin County 3

Erie County 1

Franklin County 1

Fulton County 1

Huntingdon County 2

Juniata County 6

Lancaster County 12

Lebanon County 2

Luzerne County 1

Lycoming County 3

Mifflin County 20

Montgomery County 4

Montour County 1

Northumberland County 6

Union County 7

Washington County 1

Total cases for Pennsylvania 112

South Carolina Anderson County 2

Chesterfield County 1

Saluda County 1

Spartanburg County 1
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 10

State County West Nile 

Virus

Reported 

Cases

Total cases for South Carolina 5

South Dakota Brule County 1

Total cases for South Dakota 1

Tennessee Bradley County 1

Cumberland County 1

Jefferson County 1

Loudon County 1

McMinn County 1

Monroe County 1

Rutherford County 1

Sullivan County 1

Warren County 2

Washington County 2

Total cases for 

Tennessee 12

Texas Cooke County 1

Dallas County 2

Deaf Smith County 1

Denton County 2

Hansford County 1

Harris County 1

Hidalgo County 1

Hunt County 1

Jones County 2

Lavaca County 1

Mason County 1

Montague County 1

Randall County 1

Tarrant County 1

Taylor County 1

Wichita County 1

Total cases for Texas 19

Utah Cache County 2

Duchesne County 1

Kane County 1

Salt Lake County 1
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 11

State County West Nile 

Virus

Reported 

Cases

Total cases for Utah 5

Vermont Lamoille County 1

Windham County 1

Total cases for Vermont 2

Virginia Clarke County 1

Fauquier County 1

Loudoun County 1

Page County 1

Prince George County 1

Rappahannock County 1

Smyth County 1

Warren County 1

Total cases for Virginia 8

Washington Grant County 1

Stevens County 1

Total cases for Washington 2

West Virginia Berkeley County 1

Fayette County 1

Total cases for West Virginia 2

Wisconsin Barron County 1

Dunn County 1

Winnebago County 1

Total cases for 

Wisconsin 3

Wyoming Campbell County 4

Carbon County 1

Fremont County 3

Johnson County 1

Lincoln County 1

Park County 3

Sheridan County 2

Weston County 1

Total cases for 

Wyoming 16

Total Reported West Nile Virus Equine Cases for the United States 493
2018 Summary of West Nile Virus Equine Cases in the United States

USDA-APHIS-VS 12