Histologically, numerous irregular small vesicles are found embedded in a dense stroma of connective tissue with focal mineralization. They are lined with a barely discernable inner germinal epithelium and prominent outer PAS-positive membrane, both of which are of parasitic origin. Intraluminal scoleces with golden-brown hooklets bud off. In contrast, the fibrous capsule surrounding the hydatid acts as a limiting barrier in E. granulosus infection. The unbounded invasive growth of E. multilocularis is possible due to protrusions of the germinal epithelium into the surrounding hepatic tissue.
Germinal cells reaching blood or lymphatic vessels can give rise to distant metastatic foci.
It remains unclear how and when this Barbary ape became infected with E. multilocularis onchospheres. To our knowledge, this is the first report of E. multilocularisinfection in a nonhuman primate. Echinococcosis in monkeys is very rare and the few reported cases involve E. granulosus. A literature search found that infection with Echinococcus multilocularis has been reported in a cynomolgus monkey, a gorilla, and a ring-tailed lemur. Though Echinococcus multilocularis is principally arctic, In the United States, the cycle is found in the Northern central plains and has been reported as far south as Nebraska and Illinois.