After the release of the Nurgle Battletome and Chaos Daemons Codices near the beginning of 2018, we were blessed with a plastic Great Unclean One, who's kit was accompanied by the creation of a new special character; Rotigus the Rainfather.
Also known as the Rainmaker and the Generous One, Rotigus is a Great Unclean One most attuned to the fecundity and generosity of Nurgle and, by extension, the natural world. As such, he's seen by many primitive peoples as a fertility God. But since he's still a Great Unclean One, there's an AIDS-y twist to it. For example, someone praying for more fertile livestock will find that this does happen, but the offspring produced will be malformed diseased monstrosities, or someone praying for raim after a drought will be flooded with gross and brackish waters. He, like every Great Unclean One, is creepily happy about the jobs he does, actually humming while he infects loads of people with his diseased shitwater. He is constantly surrounded by a storm of filth and disease known as Nurgle's Deluge, so merely being near him islikely to get you drowned in sewage.
In the 8th Edition Chaos Daemons Codex, it says that, after the Tau conquest of the planet Dh'arthan, a massive drought and the failure of their hydrotech forced the Earth caste farmers to convert to the natives religion and start praying for rain... only for them to learn that their fertility god was Rotigus, who quickly transformed their desert planet into a stinking bog.