Zanthi fever was a virus that targeted the empathic abilities of mature Betazoids. It caused the Betazoid to project their own emotions onto others but only in those individuals where a latent propensity for that emotion was present. A simple wide-spectrum anti-viral agent was enough to cure the condition.
In 2371, during a visit to Deep Space 9 during the Bajoran Gratitude Festival, Lwaxana Troi projected her feelings for Odo onto several members of the station's population. As a result, Jake Sisko developed feelings for Major Kira Nerys, Vedek Bareil lusted for Lieutenant Jadzia Dax, Dax became attracted to Commander Benjamin Sisko, Miles O'Brien became jealous of his wife and a colleague, Doctor Julian Bashir coupled up with Major Kira, and Quark went for Keiko O'Brien. Constable Odo seemed immune to the effects. (DS9: "Fascination")