Review of the Internal Metazoan Parasites in Domestic Rats and Mice
American Association of Zoo Veterinarians Conference 2010
D. Reavill, DVM, DABVP(Avian), DACVP, R. Schmidt, DVM, PhD, DACVP
Zoo/Exotic Pathology Service, West Sacramento, CA, USA


The pathology records of domestic mice and rats with internal metazoan infections were reviewed. The submissions were primarily pet store animals purchased as pets or as a food source for other animals (raptors, reptiles, etc). From a total of 718 rats, 42 (5.8%) were found to harbor combinations of four different endoparasites. In the 172 mice, 99 (57.5%) carried metazoan parasites.

The parasites identified in rats included Trichosomoides crassicauda (bladder thread worm, n=8), Rodentolepis (formerly Hymenolepis) nana within the small intestines (n=4), Syphacia species within the colon and/or cecum (n=28), and cysticercoid cysts (Strobilocercus fasciolaris) embedded in the liver (n=4). The parasites in mice were Rodentolepis (formerly Hymenolepis) nana within the small intestines (n=27) and Syphacia species within the colon and/or cecum (n=77).

Three of these parasites (T. crassicauda, Syphacia species, and R. nana) have a direct life cycle. After the egg is ingested, T. crassicauda migrates to the urinary tract epithelium. Dead worms can serve as a nidus for calculus formation.1 Pinworms commonly infecting laboratory rodents include the mice pinworms Syphacia obvelata and Aspiculuris tetraptera, and in rats Syphacia muris.4 Rodentolepis (formerly Hymenolepis) nana is the primary cestode (dwarf tapeworm) found in the small intestine of rats and mice. This common tapeworm has a direct and indirect life cycle as well as being zoonotic.2

Rats serve as intermediate hosts for the cat tapeworm Taenia taeniaeformis. The cysticercoid cyst (S. fasciolaris) embeds in the liver. These lesions can be associated with sarcomas from the reactive tissue around the cyst.3

Literature Cited

1.  Bowman MR, Pare JA, Pinckney RD. Trichosomoides crassicauda infection in a pet hooded rat. Vet Rec. 2004;154(12):374–375.

2.  Johnson-Delaney CA. Zoonotic parasites of selected exotic animals. Semin Avian Exotic Pet Med. 1996;5(2):115–124.

3.  Kumar JM, Reddy PL, Aparna V, Srinivas G, Nagarajan P, Venkatesan R, et al. Strobilocercus fasciolaris infection with hepatic sarcoma and gastroenteropathy in a Wistar colony. Vet Parasitol. 2006;141(3–4):362–367.

4.  Perec-Matysiak A, Okulewicz A, Hildebrand J, Zalesny G. Helminth parasites of laboratory mice and rats. Wiad Parazytol. 2006;52(2):99–102.


Speaker Information
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Drury Reavill, DVM, DABVP (Avian), DACVP
Zoo/Exotic Pathology Service
West Sacramento, CA, USA

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