The blight was created by the Dominion to punish the Teplan for their resistance against the Dominion during the 22nd century. The disease had a hundred percent infection and fatality rate. The disease reacted negatively to electromagnetic radiation that was emitted by advanced medical technology, such as Federation technology, that quickened the stages of the disease.
In 2372, Doctor Julian Bashir managed to create an antigen that could inoculate babies while they were still in the womb, meaning they were born free of the disease. While the current generation could not be helped future generations had the possibility of living free of the blight. (DS9: "The Quickening")
By 2411 there were still surviving pockets of blighted Teplans and the virus that caused it had mutated it, allowing it to infect even vaccinated individuals. However, a Starfleet team from a flotilla led by Commodore Tyria Sark detected the problem, and Lieutenant Hantra Faz, a pharmacologist on USS McCoy, was assigned to update the vaccine. (The War of the Masters: "A Good Compromise")
The pathogen that caused the Teplan blight was a lysogenic virus, custom-built as a biogenic weapon by the Dominion. The virus was transmitted to the victim from his or her mother during the third trimester of pregnancy. It stained the skin in a dark, veiny pattern during the initial infection, then went dormant for potentially many years. When its repressor genes deactivated later in life, the secondary infection caused a fatal degenerative disorder of the connective tissue.