Morphogenic virus
The morphogenic virus was a degenerative disease created by the rogue Federation agency Section 31 as a means to attack the Founders of the Dominion, and end the threat they posed to the Alpha Quadrant.
In 2372, when the Founders were threatening Earth with apparent invasion, Captain Benjamin Sisko and Odo, a Founder serving the Bajoran government, provided assistance in trying to hunt down the changelings. Odo submitted to a thorough bio-examination at Star Fleet Medical in the hopes of helping Star Fleet discover a means of detecting or stopping the Founders. However, at the same time, Section 31 secretly infected Odo with the disease in the hopes that Odo would carry it back to the Great Link, where it would infect all of the remaining Founders. Odo did just that when he was forced to return to the Link late that year to face 'judgment' for killing another Founder.
The disease took time to incubate, and only progressed as the individual Founders changed form; thus, more rapid form-changing would lead to a more rapid progression of the disease. The disease first began to manifest itself in a Female Founder in early 2375. Odo first learned of the existence of the virus at this time due to his contact with a Vorta named Weyoun, though he still was not aware that he was a carrier. To avoid showing weakness, the Founders attempted to hide the existence of the disease from their Cardassian allies. Meanwhile, they had teams of Vorta doctors working day and night to find a cure.
Ironically, it was a Federation doctor who was able to cure the Founders. Julian Bashir realized that Section 31 was responsible for the disease. He captured the Section 31 agent Luther Sloan, and used a multitronic engramatic interpreter to extract the cure. The Federation Council debated giving the cure to the Founders, but decided that it would give them the upper hand.
The cure to the morphogenic virus was instrumental in ending the Dominion War. After the Dominion retreat to Cardassia Prime, Odo linked with the Female Founder, curing her of the disease. The Founder then ordered the Dominion forces to surrender. Odo returned to the Great Link and cured the rest of his kind.
