Three cases of EEE have been confirmed in Michigan, the state's Health and Community Services Department announced on Friday.
The agency reminded residents to take precautions to prevent mosquito bites.
In Massachusetts, seven people have been diagnosed with the virus, including a 5-year-old girl.
Symptoms begin with the sudden onset of headaches, high fever, chills and vomiting about four to 10 days after the bite of an infected mosquito, according to the Centers for Disease Control and Prevention. The illness could then progress into disorientation, seizures and coma, according to the agency.
The virus can cause inflammation in the brain and kills about a third of the people who contract it, according to the CDC.
Many who survive end up having mild to severe brain damage.
There is no treatment or vaccination for EEE, and children and elderly people tend to have the worst prognosis, Dr. Todd Ellerin, director of Infectious Diseases and vice chair of the Department of Medicine at South Shore Health in Massachusetts, told ABC News last month.
EEE can affect humans, horses and birds. About 90% of horses that test positive for the virus die, according to Michigan health officials.
In July, Florida health officials announced an uptick in sentinel chickens that tested positive for the virus. The chickens show the presence of the virus, but they don't develop the symptoms associated with them, according to the American Veterinarian.
The virus cannot be transmitted from person to person or horse to person, Michigan health officials said.
Typically, about five to 10 cases of EEE in humans are reported in the U.S. annually, according to the CDC.