2022 Equine Infectious Anemia Cases 

in the United States

January 1 – December 31, 2022 

This document summarizes equine infectious anemia (EIA) cases and testing reported in the United 

States during 2022. Following current guidance, the over 400 EIA-approved laboratories sent monthly 

summary testing data directly to APHIS Veterinary Services (VS). All positive cases were confirmed by 

the National Veterinary Services Laboratories (NVSL), and the VS Equine Health Team compiled case 

information in collaboration with State animal health officials.

Reporting of EIA testing is summarized on a calendar-year basis. During 2022, a total of 1,349,759 EIA 

tests were conducted, resulting in detection of 96 positive horses on 45 premises (Table 1). These 

results compared to 1,416,809 tests and 103 positives on 54 premises in 2021. Figure 1 is a map 

depicting reported numbers of horses and premises testing positive for EIA by state and county in 2022.

Figure 2 presents a summary of EIA testing from 2003–2022. Historical data and additional information 

on EIA are available online at https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-diseaseinformation/equine/eia. 

Table 1. Test results reported for equine infectious anemia in the United States, 2022 

State Tests Performed Positive Horses Positive Premises

Alabama 20,209 0 0

Alaska 654 0 0

Arizona 18,745 7 1

Arkansas 32,461 0 0

California 21,603 40 9

Colorado 25,650 1 1

Connecticut 9,204 0 0

Delaware 3,642 0 0

Florida 104,167 0 0

Georgia 38,896 1 1

Hawaii 388 0 0

Idaho 13,662 0 0

Illinois 25,662 1 1

Indiana 16,888 0 0

Iowa 19,974 1 1

Kansas 16,735 0 0

Kentucky 66,303 1 1

Louisiana 25,963 0 0

Maine 5,760 0 0

Maryland 23,237 0 0

Massachusetts 14,180 0 0

Animal and Plant 

Health Inspection 

Service 

Veterinary 

Services 

June 2023
2022 Summary of Equine Infectious Anemia Cases in the United States

USDA-APHIS-VS 2 

Michigan 31,811 0 0

Minnesota 28,941 0 0

Mississippi 18,534 0 0

Missouri 53,731 1 1

Montana 16,704 0 0

Nebraska 10,410 0 0

Nevada 13,907 1 1

New Hampshire 6,847 0 0

New Jersey 17,919 0 0

New Mexico 13,581 1 1

New York 40,293 0 0

North Carolina 52,650 16 7

North Dakota 6,714 0 0

Ohio 40,329 1 1

Oklahoma 55,399 0 0

Oregon 8,462 0 0

Pennsylvania 46,036 0 0

Rhode Island 1,901 0 0

South Carolina 28,766 7 3

South Dakota 8,652 0 0

Tennessee 43,465 0 0

Texas 179,765 14 13

Utah 8,348 1 1

Vermont 5,867 0 0

Virginia 38,833 0 0

Washington 6,624 2 2

West Virginia 8,537 0 0

Wisconsin 36,778 0 0

Wyoming 15,905 0 0

Puerto Rico 58 0 0

U.S. Virgin Islands 9 0 0

U.S. Totals 1,349,759 96 45
2022 Summary of Equine Infectious Anemia Cases in the United States

USDA-APHIS-VS 3

Figure 1. Reported numbers of horses and premises testing positive for EIA by state and county, 2022

Although the current prevalence of EIA in the U.S. equine population remains very low, at an estimated 

national prevalence of around 0.004 percent, the epidemiology of EIA-positive cases has shifted in 

recent years. Most EIA cases were previously found to occur from natural transmission by biting fly 

vectors in untested and undertested populations. Increasing cases of iatrogenic transmission (disease 

resulting from medical activity) are now being identified. 
2022 Summary of Equine Infectious Anemia Cases in the United States

USDA-APHIS-VS 4

Figure 2. Reported numbers of EIA tests and positive cases in the United States, 2003–2022

In 2022, there were 84 confirmed cases of EIA in either current or former Quarter Horse racehorses 

where iatrogenic transmission was the method of disease spread. Iatrogenic transmission in this equine 

population is occurring through unhygienic practices by horse trainers and owners. Practices include reuse of needles, syringes, and IV sets; administration of blood transfusions from untested donor horses;

use of illegal blood products from other countries; and infectious blood contamination of multi-dose 

drug vials. 

Some of the iatrogenic transmission cases in the Quarter Horse racehorse population are found in 

horses participating in unsanctioned racing. However, there are also recognized crossover cases 

between unsanctioned and sanctioned racing in some parts of the United States. Cases in sanctioned 

Quarter Horse racehorses with no obvious connection to unsanctioned racing have also been identified. 

EIA-positive cases in this emerging high-risk population are frequently found in clusters, indicating a 

horse trainer or owner repeatedly using unhygienic practices which caused disease spread to multiple 

horses. These cases are preventable by good hygienic practices and basic biosecurity measures. Thus, 

increased education and outreach to trainers and owners of Quarter Horse racehorses are needed to 

mitigate the continued spread of EIA. 

Of the remaining 12 positive EIA cases identified in the United States during 2022, one (1) originated

from untested/undertested herds where natural transmission was likely occurring over a long period, 

four (4) horses were suspected or confirmed to have been illegally moved into the United States from 

Mexico, and seven (7) horses were infected from an unknown/undetermined source.

0

500

1000

1500

2000

2500

Number of Tests x 1000 Number of Test-positive Horses
2022 Summary of Equine Infectious Anemia Cases in the United States

USDA-APHIS-VS 5

Current APHIS guidance for EIA-approved laboratories now provides more comprehensive EIA testing 

data than previously existed. Figure 3 captures the number of EIA tests performed in 2022 by month. 

April, March, and May, respectively, were the busiest months when EIA testing occurred in 2022.

Figure 3. Reported numbers of EIA tests performed in the United States in 2022 by month

Two EIA test types are authorized for use by approved laboratories in the United States: 1. agar gel 

immunodiffusion (AGID) tests, commonly called Coggins tests, and 2. enzyme-linked immunosorbent 

assay (ELISA) tests. Figure 4 depicts the number of AGID tests performed throughout the United States

in 2022, compared to the number of ELISA tests performed. Both test assays were used in 2022 with 

nearly equal frequency. 

Figure 4. Reported numbers of AGID and ELISA EIA tests performed in the United States in 2022

0

20000

40000

60000

80000

100000

120000

140000

160000

180000

200000

EIA Tests Performed in 2022 by Month

AGID & ELISA EIA Tests Performed in 2022

AGID Tests

ELISA Tests
2022 Summary of Equine Infectious Anemia Cases in the United States

USDA-APHIS-VS 6 

Figure 5. Reported numbers of AGID and ELISA EIA tests performed by state of horse residence in 2022 

0 20000 40000 60000 80000 100000 120000 140000 160000

Alabama

Alaska

Arizona

Arkansas

California

Colorado

Connecticut

Delaware

Florida

Georgia

Hawaii

Idaho

Illinois

Indiana

Iowa

Kansas

Kentucky

Louisiana

Maine

Maryland

Massachusetts

Michigan

Minnesota

Mississippi

Missouri

Montana

Nebraska

Nevada

New Hampshire

New Jersey

New Mexico

New York

North Carolina

North Dakota

Ohio

Oklahoma

Oregon

Pennsylvania

Puerto Rico

Rhode Island

South Carolina

South Dakota

Tennessee

Texas

Utah

Vermont

Virgin Islands

Virginia

Washington

West Virginia

Wisconsin

Wyoming

AGID & ELISA EIA Tests Performed in 2022 by State of Horse Residence

AGID Tests ELISA Tests
2022 Summary of Equine Infectious Anemia Cases in the United States

USDA-APHIS-VS 7

Figure 5 shows the number and type of EIA assays used to test resident horses in each state. Twentyseven States, Puerto Rico, and the Virgin Islands, reported fewer than 20,000 EIA tests performed on 

their horse populations in 2022. Twenty States reported between 20,000 and 60,000 EIA tests 

performed on their horse populations in 2022. Three (3) States—Florida, Kentucky, and Texas—reported 

over 60,000 EIA tests performed on their horse populations in 2022. Horse populations in 23 states were 

tested more frequently using an ELISA assay than the AGID assay. In comparison, horse populations in 

27 states, Puerto Rico, and the Virgin Islands were tested more frequently using the AGID assay 

compared to an ELISA assay.