Kareel was a female Trill who became the host of the Odan symbiont in 2367. (TNG episode: "The Host")

Odan was near death after Beverly Crusher was forced to remove the symbiote from Will Riker in order to save the human's life. The USS Enterprise-D rendezvoused with the Trill vessel and Kareel transported over, surprising Beverly Crusher who had expected another male host. After Kareel was implanted with the Odan symbiont, she discussed Odan's romance with Crusher, but Crusher could not deal with how things could change again. (TNG episode: "The Host")

In 2369 when the Tantalus VII penal colony was evacuated due to a roaming pulsar, Odan found out the USS Enterprise would be involved and volunteered to serve as Trill's representative watching over criminal Keb Dalor. Dalor, while using Jean-Luc Picard as a host briefly considered transferring into Kareel. Odan and Beverly Crusher worked together to assist the rest of the Enterprise crew in stopping Dalor; Odan and Crusher left things open as to one day rekindling their romantic relationship. (TNG comic: "A House Divided")

Kareel was killed by a terrorist faction led by the criminal Verad Kalon in 2376. Odan survived, and went on to a new host, a security officer named Kinjer. (TNG/DS9 comic series Divided We Fall)