The Fossil Disease is a plague only appearing in the anime (2003). In the 2003 anime, the village of Lujon and Lydia was hit with an epidemic of it. It is a crippling disease that affects the body and an individual with the disease will be physically paralysed and die. The individual's skin will horrifyingly start to react and harden, and will stick out. The appearance of the infected area looks as if it is fossilized, hence the name. The infected area will then spread throughout the body and the patient will soon die moments later. The effects are very painful.
At one point, Lust leaves the village celebrations when it seems that Lujon has cured most of the sufferers using the Stone she had given him. She meets up with Envy, who had been disguised as an old man, and Envy explains that he had spread the pestilence in the region in the hopes of driving alchemists in the area to attempt to create the Philosopher's Stone.
It is not clear how the infection is transmitted, however. Near the end of the episode (Episode 35: Reunion of the Fallen), Lust kills Lujon after he embraces her believing that she returns his love. Lydia arrives with Ed, Al, and Winry soon after, and they find all of the village dead from Fossil Disease. Lydia runs ahead of Ed, Al and Winry, and finds Lujon, also grotesquely disfigured by Fossil Disease, and she embraces his corpse. A moment later, the Resembool teens find the couple, and Lydia is also dead, her body stricken with the same plague, yet, none of the Resembool gang appear to contract any symptom of Fossil Disease. This could imply that the disease is non-infectious.