CASS COUNTY, MI -- A fifth person has died from the mosquito-borne illness Eastern equine encephalitis (EEE).

The death of an adult in Cass County was confirmed by Lynn Sutfin, a Michigan Department of Health and Human Services spokeswoman. She could not confirm the age or gender of the deceased.

The person who died in Cass County began showing symptoms prior to Sept. 30, Sutfin said, and the case was included in the tally of human cases in an Oct. 8 MDHHS news release.

In total, 10 human cases of EEE have been reported in Barry, Berrien, Calhoun, Cass, Kalamazoo and Van Buren counties, according to MDHHS. Including the most recent reported death, five of the 10 cases were fatal.

A horse was also infected with EEE in Allegan County, according to a Oct. 14 MDHHS press release, bringing the total number of confirmed animal cases in Michigan this year to 40. The 40 infected animals were reported in 16 counties: Allegan, Barry, Berrien, Calhoun, Cass, Genesee, Jackson, Kalamazoo, Kent, Lapeer, Livingston, Montcalm, Newaygo, St. Joseph, Tuscola and Van Buren, according to MDHHS.

Health officials have called the 2019 outbreak of EEE in Michigan the worst in the state’s history.

The virus is considered to be “one of the most dangerous mosquito-borne diseases in the United States” and has a 33 percent fatality rate in people who become seriously ill and a 90 percent fatality rate in horses that become ill, according to MDHHS.

Only 4-5% of people will be become sick when infected with the virus, according to information provided by the MDHHS. Those infected usually do not show symptoms; however, those who do will develop chills, fever, weakness, muscle and joint pain.

Less than 1% of people who are infected will develop a serious neurological illness that causes inflammation of the brain or surrounding tissues, according to MDDHS. About 30% of people who develop neurological infection due to Eastern equine encephalitis will die.

Aerial spraying of the Merus 3.0 organic pesticide — which contains 5% pyrethrin — covered 557,000 acres targeting 14 counties in Michigan. Spraying concluded on Oct. 7, but the Kalamazoo and Portage area remains at risk given that residents opt-ed out of the spraying.

The state health department is still warning residents to avoid outdoor activities after dusk as well as encouraging the use of bug repellent, dumping standing water and wearing pants and long sleeves.