Doctors at Texas Health Harris Methodist Hospital confirmed they are treating a human case of West Nile virus.
The hospital could not elaborate on the case because of privacy laws.
NBC 5 learned about the case from the family of the 58-year-old patient. They said by phone that he became ill on May 6 and was diagnosed with West Nile virus on May 17.
Neighbors on his street near the border of Tarrant and Parker counties said the news is alarming.
"I'm a stay-at-home mom, and my daughter and I stay outside all day when the weather's good," Michelle Blackmon said. "It's kind of scary because I don't want anything happening to her."
The man's family said he has also been diagnosed with Guillain-Barre syndrome. According to the U.S. National Library of Medicine's website, it is a serious disorder that occurs when someone's immune system mistakenly attacks part of the nervous system.
The man remains in critical condition.