JPC SYSTEMIC PATHOLOGY
DIGESTIVE SYSTEM
October2021
D-P18 (NP)

 

Signalment (JPC #287220):  Laboratory albino mouse

 

HISTORY:  None

 

HISTOPATHOLOGIC DESCRIPTION:  Small intestine:  Multifocally expanding the lamina propria of occasional scattered individual villi are 80-100 um diameter, oval cysticerci that lack a pseudocoelom and digestive tract and have a thin, 1-2 um wall surrounding an eosinophilic tegument, basophilic calcareous corpuscles, and a single invaginated scolex armed with refractile hooklets and one to four muscular suckers (depending on plane of section).  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)

 

GENERAL DISCUSSION:

• 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 infect the small intestine in mice

 

LIFE CYCLE:

• 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 (or cysticerci) (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:

Severe infection

• 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

 

DIFFERENTIAL DIAGNOSIS:

• 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); infects gallbladder, bile and pancreatic ducts, and duodenum; results 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
• Cysticercus fasciolaris (D-P22, larval stage of cat tapeworm Taenia taeniaeformis): Mice may serve as intermediate host for the cat tapeworm; liver is usual location for strobilocerci (larval stage); source of infection is cat feces

 

COMPARATIVE PATHOLOGY:

• Reported in rodents (mice, rats, hamsters, gerbils, and rarely guinea pigs), nonhuman primates (prosimians, 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 (Muehlenbachs, N Engl J Med, 2015)

 

REFERENCES:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4^th Ames, IA: John Wiley & Sons, Inc.; 2016:85-86, 153, 205.
2. Bowman DD. Georgis' Parasitology for Veterinarians. 10th ed. St. Louis, MO: Elsevier; 2014:154.
3. Crouch EEV, Hollinger C, Zec S, McAloose D. Fatal Hymenolepis nana cestodiasis in a ring-tailed lemur (Lemur catta). Vet Pathol. 2021: 3009858211042580. Epub ahead of print.
4. Gardiner CH, Poynton SL. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC:Armed Forces Institute of Pathology;1999:52.
5. 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.
6. 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.

 

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