Echinococcus multilocularis: A fatal tapeworm infection in a dog
Animal Health Laboratory, University of Guelph, Guelph, ON
AHL Newsletter 2022;26(4):22.
A 2-year-old male neutered Boxer dog presented to the referring veterinarian for abdominal distention and lethargy. Through various tests, including PCR, the dog was diagnosed with multiple hepatic/abdominal Echinococcus multilocularis parasitic cysts. After attempted treatments with alcohol ablation of the cysts without recovery and continued decline, humane euthanasia was elected.
At postmortem, there was compression of all abdominal organs by three large fluid-filled cysts (Fig. 1A). All cysts had a mottled white and red, nodular, heavily vascularized fibrous capsule. The cyst walls were thick and spongy with numerous fluid-filled pockets, and multiple foci of necrosis. The largest cyst measured 22.0 cm x 17.0 cm x 18.0 cm, and two of the three cysts nearly replaced the left medial and caudate process of the caudate lobes of the liver (Fig. 1B). The third cyst was located within the mesentery of the abdomen. There were many abdominal adhesions and generalized enlargement of all abdominal lymph nodes.
Histological sections of the cysts revealed massive regions of necrosis, and inflammation characterized by fragmented, eosinophilic hyaline membranes with numerous deeply basophilic calcareous corpuscles. Outlines of metacestode protoscoleces with few distinguishable refractile parasite rostellar hooks, fibrin, cellular debris, epithelioid macrophages, neutrophils and fibrosis were also present.
E. multilocularis is a zoonotic tapeworm found in North America and Europe, and is considered endemic in wildlife within defined regions of Canada. Wild canids (primarily foxes and coyotes) serve as the definitive host for the parasite. Adult tapeworms reside in the small intestine of these species, and the eggs passed in feces are immediately infective to intermediate hosts (mainly small rodents). Parasitic cysts filled with larvae grow within the abdominal organs of the intermediate rodent hosts. The rodent is then ingested by a wild canid, and the lifecycle begins again.
Domestic dogs are also considered to be a definitive host; however, deviations to the life cycle can occur, causing domestic canines to develop cysts (often hepatic) with intermediate parasite stages. E. multilocularis poses a potentially fatal zoonotic risk, as humans can become infected and develop parasitic cysts by ingesting eggs shed by an infected domestic dog. AHL
Figure 1. E. multilocularis cysts. A. Multiple hepatic and mesenteric cysts in situ within the abdominal cavity. B. Two large cysts replacing liver lobes and a third mesenteric cyst.