Alveolar Hydatid (AHD) disease results from being infected with the larval stage of Echinococcus multilocularis, a microscopic tapeworm (1-4 millimeters) found in foxes, coyotes, dogs, and cats. Although human cases are rare, infection in humans causes parasitic tumors to form in the liver, and, less commonly, the lungs, brain, and other organs. If left untreated, infection with AHD can be fatal.