2019 Summary of Eastern Equine 

Encephalitis Cases in the United States

January 1 – December 31, 2019

This report is a descriptive summary of U.S. Eastern equine encephalitis (EEE) 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 used to 

track and report arboviral activity in humans and animals. During the transmission season, VS 

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

posts the number of confirmed cases to the USDA equine information Web site 

https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/animal-disease-information/equine. This site 

also provides specific case definitions. In this document, ‘reported cases’ of EEE may include 

presumptive positive and confirmed positive cases. 

In 2019, 184 equine cases of EEE were reported from 24 States. Figure 1 shows the annual number of 

equine EEE cases reported in the U.S. from 2006 through 2019. Figure 2 shows the number of equine 

EEE 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# 

20-069

111

206

185

301

247

60

209

192

136

70

118

86

107

184

0

50

100

150

200

250

300

350

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

Equine Cases of EEE

EEE Cases
2019 Summary of Eastern Equine Encephalitis Cases in the United States 

USDA-APHIS-VS 2 

Figure 1. Reported U.S. equine cases of Eastern equine encephalitis, 2006-2019

Figure 2. Distribution of reported equine EEE cases in 2019 (184 total cases) 

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

State County Eastern Equine Encephalitis 

Reported Cases 

Alabama Houston County 1 

Total Cases for Alabama 1 

Arkansas Arkansas County 1 

Hot Spring County 1 

Lonoke County 1 

Pulaski County 2 

Saline County 2 
2019 Summary of Eastern Equine Encephalitis Cases in the United States 

USDA-APHIS-VS 3 

State County Eastern Equine Encephalitis 

Reported Cases 

Total Cases for Arkansas 7 

Connecticut New London County 4 

Tolland County 1 

Windham County 1 

Total Cases for Connecticut 6 

Florida Bay County 2 

Calhoun County 3 

Citrus County 1 

Clay County 1 

Columbia County 1 

DeSoto County 2 

Gulf County 1 

Holmes County 3 

Jackson County 1 

Levy County 1 

Madison County 1 

Osceola County 1 

Palm Beach County 1 

Pasco County 1 

Polk County 1 

Putnam County 2 

St. Johns County 1 

Suwannee County 2 

Washington County 2 

Total Cases for Florida 28 

Georgia Dooly County 1 

Lowndes County 2 

Total Cases for Georgia 3 

Indiana Elkhart County 11 

Lagrange County 3 

Total Cases for Indiana 14 

Louisiana Allen Parish 1 

Assumption Parish 2 

Avoyelles Parish 1 

Beauregard Parish 2 

Caddo Parish 4 

De Soto Parish 2 

Iberville Parish 1 

Lafourche Parish 2 
2019 Summary of Eastern Equine Encephalitis Cases in the United States 

USDA-APHIS-VS 4 

State County Eastern Equine Encephalitis 

Reported Cases 

Morehouse Parish 1 

 Pointe Coupee 

Parish 

1 

Rapides Parish 1 

Red River Parish 1 

St. Mary Parish 1 

St. Tammany Parish 2 

Tangipahoa Parish 2 

Terrebonne Parish 3 

Union Parish 1 

Webster Parish 1 

 West Baton Rouge 

Parish 

1 

Total Cases for Louisiana 30 

Massachusetts Essex County 1 

Middlesex County 1 

Norfolk County 1 

Worcester County 5 

Total Cases for Massachusetts 8 

Maryland Worcester County 1 

Total Cases for Maryland 1 

Maine York County 1 

Total Cases for Maine 1 

Michigan Allegan County 1 

Barry County 2 

Calhoun County 1 

Cass County 2 

Jackson County 4 

Kalamazoo County 6 

Kent County 1 

Lapeer County 1 

Leelanau County 1 

Livingston County 1 

Montcalm County 1 

Newaygo County 1 

St. Joseph County 6 

Tuscola County 1 

Total Cases for Michigan 29 

Minnesota Otter Tail County 2 

Total Cases for Minnesota 2 
2019 Summary of Eastern Equine Encephalitis Cases in the United States 

USDA-APHIS-VS 5 

State County Eastern Equine Encephalitis 

Reported Cases 

Mississippi Greene County 1 

Hancock County 1 

Jackson County 5 

Kemper County 1 

Total Cases for Mississippi 8 

North Carolina Cumberland County 1 

Total Cases for North Carolina 1 

New Hampshire Hillsborough County 1 

Rockingham County 1 

Total Cases for New Hampshire 2 

New Jersey Atlantic County 1 

Burlington County 1 

Camden County 1 

Monmouth County 1 

Morris County 1 

Ocean County 5 

Salem County 1 

Total Cases for New Jersey 11 

New York Ontario County 1 

Oswego County 4 

Total Cases for New York 5 

Ohio Ashtabula County 3 

Portage County 2 

Total Cases for Ohio 5 

Pennsylvania Carbon County 2 

Luzerne County 1 

Mercer County 1 

Total Cases for Pennsylvania 4 

Rhode Island Washington County 1 

Total Cases for Rhode Island 1 

South Carolina Beaufort County 2 

Chesterfield County 1 

Marlboro County 1 

Sumter County 1 

Total Cases for South Carolina 5 

Tennessee Gibson County 1 

Total Cases for Tennessee 1 

Texas Liberty County 1 

Montgomery County 1 
2019 Summary of Eastern Equine Encephalitis Cases in the United States 

USDA-APHIS-VS 6 

State County Eastern Equine Encephalitis 

Reported Cases 

Orange County 3 

Smith County 1 

Total Cases for Texas 6 

Wisconsin Barron County 1 

Green Lake County 1 

Taylor County 1 

Walworth County 1 

Waushara County 1 

Total Cases for Wisconsin 5 

Total Reported Eastern Equine Encephalitis Cases for the 

United States 

184 

The 2019 case count of EEE cases in equids throughout the U.S. did not set a high historical record; 

however, there are several observations surrounding EEE infections that made this year particularly 

interesting for both human medical doctors and veterinarians. Thirty-eight human cases of EEE with 15 

fatalities were confirmed in 10 States. This is a record-setting number of human cases, with the next 

highest yearly total of 15 cases recorded in 2012 and an average of 7 EEE cases confirmed annually from 

2009-2018. 

Another unexplained yet interesting finding is the number of equine West Nile Virus (WNV) cases 

compared to the number of equine EEE cases in 2019. Historically, the annual WNV case counts in 

equids have been at least double or more the total number of EEE case counts. In 2019, a complete 

reversal of these disease totals occurred, with 90 WNV equine cases recorded compared to 184 EEE 

equine cases. Finally, the number of EEE cases confirmed and reported in alternate and wildlife species 

has not previously been seen at such a high level and in so many different species as during 2019. 

When spikes in human cases of EEE occur, causes may include environmental and viral factors, from 

weather and geographic features to new EEE strains infecting migratory birds and circulating among 

them and mosquito populations.1 Like equids, humans are a dead-end host for the virus, which is 

predominantly spread by mosquitoes. No commercial vaccine is available for people. Thus, EEE 

infection often causes death or leads to significant neurological deficits for survivors, making it one of 

the worst viral encephalitides that people can acquire. 

EEE is also a deadly disease in equids, where mortality rates can approach 90 percent in unvaccinated 

animals. This susceptibility to the virus makes equids a recognized EEE sentinel species for the human 

population. The main public health purpose of confirming and reporting equine EEE cases is to inform 

human surveillance efforts. Because equine commercial vaccines are available and convey good 

protection against EEE infection, reported cases of EEE in equids tend to be in unvaccinated or undervaccinated animals. Equine vaccination practices effective against new and established strains of EEE 

may explain, in part, why overall numbers of equine EEE cases did not show a similar annual spike as 

reported in humans or additional species. 
2019 Summary of Eastern Equine Encephalitis Cases in the United States 

USDA-APHIS-VS 7 

1. Tan Y, Lam TT, Heberlein-Larson LA, et al. Large-Scale Complete-Genome Sequencing and Phylodynamic Analysis of Eastern 

Equine Encephalitis Virus Reveals Source-Sink Transmission Dynamics in the United States. J Virol. 2018;92(12):e00074-18. 

Published 2018 May 29. doi:10.1128/JVI.00074-18