Eastern Equine Encephalitis (EEE) is a virus that is spread by mosquitoes. It is carried by many species of native songbirds, and sometimes will cause serious neurologic illness in the rare cases of people and horses that become infected. It typically shows up in mid to late summer in this area of the northeast, but this year it looks like EEE is more active and in more areas than previous years.

As of September 5, there were positive mosquito pools in Suffolk (Manorville) Oswego, Onondaga, and Madison Counties, and 5 horse cases: 4 from Oswego and one from Ontario. Pesticide spraying has already been done in Cicero Swamp (Onondaga County) and on Long Island (Suffolk) to combat infected mosquitoes.

Most wildlife do not become ill when infected with EEE. There are some reported cases in white-tailed deer and non-native game birds, such as pheasants. Our program will be keeping an eye out for suspect cases, and testing any animals that have clinical signs.  

Current map of reported EEE cases by county, courtesy of CDC ArboNET
Current map of reported EEE cases by county, courtesy of CDC ArboNET

This level of activity, measured in the number of cases and the number of positive mosquitoes, is concerning health officials in our border states of New Jersey, Massachusetts and Connecticut.

Massachusetts EEE Risk Categories

Connecticut EEE Advisory

In New York, mosquitoes infected with EEE are typically only seen in the counties around the Cicero Swamp- Oswego, Oneida, Madison, and Onondaga. In 2014, Chautauqua County reported positive mosquitoes and a case in a horse. The Department of Health in New York reports the results of weekly mosquito testing.

2019 EEE Virus Surveillance Summary map
2019 EEE Virus Surveillance Summary map

How to cite this page

We encourage and permit the free use of these wildlife health materials for educational purposes with acknowledgment of the NYS Wildlife Health Program as the source. Please let us know when and where you used them. Email us at cwhl@cornell.edu.

Bunting, B. (2019, September 12). On the Lookout for Eastern Equine Encephalitis. NYS Wildlife Health Program. https://cwhl.djcase.com/article/lookout-eastern-equine-encephalitis. Accessed Date: September 26, 2025.