In October of 2022, an eastern chipmunk from Port Perry was brought to a local wildlife rehabilitation centre. The small animal appeared to be in pain and had an enlarged and abnormal mass in its abdomen. The wildlife rehabilitator opted to humanely euthanize the chipmunk and send the carcass to CWHC, strongly suspecting an Echinococcus multilocularis infection.
Upon gross examination by our pathologist, changes consistent with an E. multilocularis infection were identified immediately. Filling much of the abdomen and displacing the organs was a large mass composed of innumerable 2-3 mm diameter cysts. On cut section, the cysts contained serous fluid and 1-2 mm long white structures (presumably larval tapeworms). A sample of the cysts were sent for additional testing and found to be positive for Echinococcus multilocularis. Infection with E. multilocularis can lead to severe internal disease with extensive cyst formation (alveolar hydatid cysts), which often displace the normal viscera and can eventually lead to the death of the affected rodent. Unfortunately for this chipmunk, this is thought to be the cause of death as there were no other signs of abnormalities upon examination.
Echinococcus multilocularis is a small tapeworm found in the intestinal tract of infected canines and domestic dogs. The lifecycle of this tapeworm includes a mature stage in the definitive carnivore host, and an immature stage in an intermediate host – usually a prey species such as a small rodent. In this intermediate stage, the tapeworms develop in slowly growing cystic structures resembling a tumor. The lifecycle is usually completed once the carnivore eats the infected rodent.
Public Health Implications
Although we have known that this parasite has been present in the environment for years (Kotwa et al. 2019), this recent case (and the second one discovered in a chipmunk in Ontario; French et al. 2018) reminds us to be vigilant. This parasite is a public health concern, due to its ability to infect people. Humans who accidentally ingest tapeworm eggs from carnivore feces are at risk of developing alveolar hydatid cysts in their abdomen.
Prevention starts with understanding the intersection between adequate personal hygiene and responsible pet ownership:
- Keep dogs on a leash or supervised while outdoors: do not allow dogs to feed on rodents or other wildlife. Similarly, keep cats indoors or supervised while outside.
- Respect wildlife and the law: avoid contact with wildlife, and do not feed or encourage wild animals to come close to your home or to be kept as pets.
- Maintain good hygiene by washing your hands regularly with soap and warm water and teach children the importance of washing hands to prevent infection.
Sources:
https://www.publichealthontario.ca/en/laboratory-services/test-information-index/echinococcus-cyst
http://blog.healthywildlife.ca/alveolar-hydatid-disease-in-a-chipmunk/
https://www.cdc.gov/parasites/echinococcosis/index.html
Kotwa JD, Isaksson M, Jardine CM, Campbell GD, Berke O, Pearl DL, Mercer NJ, Osterman-Lind E, Peregrine AS. Echinococcus multilocularis infection, southern Ontario, Canada. Emerging infectious diseases. 2019 Feb;25(2):265. https://wwwnc.cdc.gov/eid/article/25/2/18-0299_article
French SK, Jajou S, Campbell GD, Cai HY, Kotwa JD, Peregrine AS, Jardine CM. Echinococcus multilocularis in a wild free-living eastern chipmunk (Tamias striatus) in Southern Ontario: A case report and subsequent field study of wild small mammals. Veterinary Parasitology: Regional Studies and Reports. 2018 Aug 1;13:234-7. https://www.sciencedirect.com/science/article/pii/S2405939018300893?via%3Dihub