From Dragon Ball Encyclopedia
Aquamist (アクアミスト, Akuamisuto; FUNimation "Black Water Mist") is an evil mist that Garlic Jr. uses to turn anyone who breathes it in evil.
The Aquamist had once belonged to Garlic. Following Garlic's imprisonment and death, Kami hid it at the Heavenly Realm. When Garlic Jr. took over the Heavenly Realm, he found and released the Aquamist onto Earth. Those who breathed in the Aquamist turned evil and became Vampire-like, worshipping Garlic Jr. and the Spice Boys. In addition, anyone bitten by someone infected by the Aquamist became exactly like them. Son Chichi, Bulma Brief, Yamucha, Turtle Hermit, Oolong, and Puar were infected by the Aquamist and attacked Son Gohan, Kuririn, and Maron. Piccolo was bitten by them and pretended to be infected when in reality it had no effect on him, either because Namekians were immune (if they were, it contradicted Spice's line "Piccolo's Namek body is having a strong reaction to the venom", although this appears more as an observation rather than a fact and he could have been mistaken) or because Piccolo was once evil himself. As such, when he bit Kuririn, Kuririn was not affected and only pretended to be as Piccolo told him telepathically. They pretended to be infected as a plan to get closer to Garlic Jr. and rescue Kami and Mister Popo, whom Garlic Jr. had trapped inside bottles.
The only thing that could negate the Aquamist was the Sacred Water, however, it would be useless after 24 hours of infection. Kami and Popo were able to get through the resting place of the former Kami to release the Sacred Water through the Seven Air Currents, restoring everyone on Earth back to normal.
Gohan, Piccolo, Kuririn, Maron, Icarus, Karin, Yajirobe, Kami, and Popo were the only ones on Earth (aside from two unnamed people who were attacked by Cats and Mice and presumably became infected) who had not gotten infected. Son Goku was in space at this time, presumably on Planet Yardrat, and Vegeta was looking for Goku in space.
Some animals had not been reached by the Sacred Water and were still infected, and therefore a danger to the uninfected, in Dragon Ball Z: The Legacy of Goku II.