JPC SYSTEMIC PATHOLOGY
Signalment (JPC #287220): Laboratory albino mouse
HISTOPATHOLOGIC DESCRIPTION: Small intestine: Multifocally expanding the lamina propria of individual villi are scattered 80-100 um diameter, oval cysticerci that lack a pseudocoelom and digestive tract and have a thin, 1-2 um wall, eosinophilic tegument, basophilic calcareous corpuscles and a single invaginated scolex armed with refractile hooklets and one to four muscular suckers. The cysticerci are surrounded by low numbers of neutrophils and eosinophils.
MORPHOLOGIC DIAGNOSIS: Small intestine, lamina propria: Cysticerci, multiple, with mild multifocal neutrophilic and eosinophilic enteritis, albino mouse, rodent.
ETIOLOGIC DIAGNOSIS: Rodentolepisial enteritis
CAUSE: Rodentolepis nana (formerly Hymenolepis, also known as Vampirolepis nana)
- Dwarf tapeworm (cestode) that can infect wild and laboratory mice and rats, hamsters, humans, and non-human primates
- Incidence in well-managed laboratory colonies is low
- All three species of tapeworms infest the small intestine
- Unique life cycle: Can be transmitted directly or utilize an arthropod as an intermediate host (flour beetles, fleas, moths)
- Direct/autoinfection: Eggs ingested by definitive host > oncospheres penetrate villi > develop into cercocystis (larval) stage in tissue > larvae re-enter intestinal lumen in 10-12 days > attach to small intestinal mucosa via scolex > become adults within 14 days
- Indirect: Eggs pass in feces > ingestion by intermediate host (grain beetle, flea) > development into infective larvae > ingestion by definitive host > larvae attach to the small intestine mucosa > become adults within 10-11 days
TYPICAL CLINICAL FINDINGS:
- Retarded growth, weight loss, and diarrhea in the mouse
- Intestinal occlusion, impaction, and death reported in hamsters
TYPICAL GROSS FINDINGS:
- Slender, white threadlike worms in small intestine (1 mm diameter)
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Cysticerci within lamina propria and adults (prominent serrated edges) in the lumen of small intestine
- Occasionally, focal granulomatous lymphadenitis and cysticerci in mesenteric lymph nodes
- Adult cestode: 1 x 25-45 mm; scolex with 4 suckers and a muscular rostellum lined with 20 to 30 hooks
- Mature proglottid: Trapezoidal; segments wider than they are long
- Oval eggs: 30 x 55 um with an oncosphere
- Embryo or oncosphere: 20 x 30 um with 3 pair of lancet-like hooks
ADDITIONAL DIAGNOSTIC TESTS:
- Identification of threadlike worms in small intestine
- Identification of eggs on fecal flotation
- Hymenolepis diminuta: No tissue stage; larger adult (4mm), intermediate forms do not appear in the mucosa; no armed scolex; primarily in rats, also identified on necropsy in gerbils
- Rodentolepis microstoma: No tissue stage; larger adult (4mm); gallbladder, bile and pancreatic ducts, and duodenum; result in inflammatory and atrophic changes in the pancreas and cholangitis
- Has direct life cycle in immunodeficient nude and NOD-scid, NOD-scid-IL-2R gamma null mice
- Taenia taeniaeformis (Cysticercus fasciolaris): Mice may serve as intermediate host for the cat tapeworm; liver is usual location for strobilocerci; source of infection is cat feces
- Reported in rodents (mice, rats, hamsters, gerbils, and rarely guinea pigs), nonhuman primates (squirrel monkey, rhesus monkey, and chimpanzee), and humans
- In humans, heavy infections can cause anorexia, vomiting, diarrhea, weight loss, and abdominal pain; immunodeficiency and autoinfection can result in heavy infections
- Single report of invasion of an HIV infected human by abnormal, proliferating, genetically altered tapeworm cells; link between infection and cancer in immunocompromised patients (N Engl J Med, 2015)
- Bowman DD. Georgis" Parasitology for Veterinarians. 10th ed. St. Louis, MO: Elsevier; 2014:264.
- Gardiner CH, Poynton SL. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC:Armed Forces Institute of Pathology;1999:52.
- Marty AM, Neafie RC. Hymenolepiasis. In: Meyers WM, ed. Pathology of Infectious Diseases. Vol I. Washington, DC: Armed Forces Institute of Pathology; 2000:197-212.
- Muehlenbachs A, Bhatnagar J, Agudelo CA, Hidron A, et al. Malignant transformation of Hymenolepis nana in a human host. N Engl J Med. 2015; 373(19):1845-1852.
- Percy DH, Barthold SW. Pathology of Laboratory Rodents and Rabbits. 4th Ames, IA: John Wiley & Sons, Inc.; 2016:85-86, 153, 205.