2019 Summary of West Nile Virus 

Equine Cases in the United States 

January 1 – December 31, 2019 

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 2019. 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 

(https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/equine). 

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 2019, 90 equine cases of WNV were reported from 25 States. Figure 1 shows the annual number of 

equine WNV cases reported in the United States from 2006 through 2019. Figure 2 shows the number of 

equine WNV cases in each State in 2019, and Table 1 provides the number of cases per county or parish 

in those States in 2019. 

 

Animal and Plant 

Health Inspection 

Service 

Veterinary 

Services 

March 2020 

CEAH Doc # 

20-071

1,086

468

179

276

125 87

627

377

141

225

380

307

493

90

0

200

400

600

800

1,000

1,200

2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019

Equine Cases of WNV 

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

USDA-APHIS-VS 2 

Figure 1. Reported U.S. equine cases of West Nile virus, 2006-2019

Figure 2. Distribution of reported equine WNV cases in 2019 (90 total cases) 

Table 1. Number of reported equine WNV cases by State and county, 2019 

State County West Nile Virus 

Reported Cases 

Alabama Marshall County 1 

 Mobile County 1 

Total cases for Alabama 2 

Arkansas Columbia County 1 

Total cases for Arkansas 1 

California Fresno County 2 

 Kern County 2 

 Madera County 2 

Merced County 1 

Riverside County 1 
2019 Summary of West Nile Virus Equine Cases in the United States 

USDA-APHIS-VS 3 

State County West Nile Virus 

Reported Cases 

Sacramento County 1 

San Bernardino County 1 

San Joaquin County 1 

Stanislaus County 2 

Tuolumne County 1 

 Ventura County 1 

Total cases for California 15 

Colorado Adams County 1 

 Garfield County 3 

 Larimer County 1 

 Las Animas County 1 

 Mesa County 1 

Montrose County 1 

Pueblo County 1 

Rio Blanco County 2 

Weld County 3 

Total cases for Colorado 14 

Connecticut Fairfield County 1 

Total cases for Connecticut 1 

Florida Brevard County 1 

 Broward County 1 

 Citrus County 1 

 Lake County 1 

 Madison County 1 

 Osceola County 1 

 Palm Beach County 1 

 St. Johns County 2 

Volusia County 1 

Total cases for Florida 10 

Iowa Davis County 1 

 Mitchell County 1 

 Union County 1 

Total cases for Iowa 3 

Idaho Canyon County 1 

 Payette County 1 

 Twin Falls County 1 

Total cases for Idaho 3 
2019 Summary of West Nile Virus Equine Cases in the United States 

USDA-APHIS-VS 4 

State County West Nile Virus 

Reported Cases 

Illinois Marion County 1 

 Wayne County 1 

Total cases for Illinois 2 

Kentucky Boyle County 1 

 Powell County 1 

Total cases for Kentucky 2 

Louisiana Beauregard Parish 1 

 Iberia Parish 1 

Total cases for Louisiana 2 

Michigan Lapeer County 1 

Total cases for Michigan 1 

Missouri Chariton County 1 

 Randolph County 1 

Total cases for Missouri 2 

Mississippi Chickasaw County 1 

Jackson County 1 

Total cases for Mississippi 2 

Montana Flathead County 1 

 Lake County 1 

Total cases for Montana 2 

New Mexico Catron County 1 

 Luna County 1 

Socorro County 1 

Total cases for New Mexico 3 

Ohio Fulton County 1 

 Morrow County 1 

 Stark County 1 

Total for Ohio 3 

Oregon Harney County 1 

Malheur County 2 

Union County 1 

Total cases for Oregon 4 

Pennsylvania Clinton County 1 

 Juniata County 1 

 Northumberland County 1 

Total cases for Pennsylvania 3 

South Carolina Pickens County 1 
2019 Summary of West Nile Virus Equine Cases in the United States 

USDA-APHIS-VS 5 

State County West Nile Virus 

Reported Cases 

Total cases for South Carolina 1 

Tennessee Robertson County 1 

Total cases for Tennessee 1 

Texas Orange County 1 

Total cases for Texas 1 

Utah Beaver County 1 

 Duchesne County 1 

 Iron County 1 

 Juab County 1 

Sevier County 1 

Uintah County 2 

Total cases for Utah 7 

Washington Franklin County 1 

 Klickitat County 1 

Total cases for Washington 2 

Wyoming Sheridan County 1 

 Washakie County 1 

Total cases for Wyoming 2 

Total Reported West Nile Virus Equine Cases for the United States 90