Etiology: Rodentolepis nana is the dwarf tapeworm and Hymenolepis diminuta is the rat tapeworm.  Both tapeworms are capable of infecting rats.

Incidence:  The incidence of parasitism is rare.

Transmission:

Indirect cycle: Transmission occurs by ingestion of infected tissues of intermediate hosts (fleas, flour beetles, cockroaches). The prepatent period is 18 – 20 days.

Direct cycle: Rodentolepis only.  Transmission occurs by ingestion of infective eggs. The prepatent period is 10 – 20 days.

Autoinfection: Rodentolepis only.  Entire life cycle occurs in small intestine of host.

Distribution:  Lower 1/3 of small intestine. In autoinfection, immature forms may be found in the upper small intestine.

Clinical Signs:  Usually there are no external signs of infection.  However, catarrhal enteritis, diarrhea, emaciation and chronic weight loss may occur with heavy infestations.

Diagnosis:

Antemortem: Fecal flotation of ova.

Postmortem: Examination of small intestinal lining and/or histopathology for adult cestodes.

Diagnostic morphology:

Adults:  Rodentolepis nana adults range from 25 to 40 mm long and less than l mm wide and have an armed rostellum (photo, left).  Since R. nana can complete its life cycle without an intermediate host, strobelocerci may be observed within the lamina propria of the small intestine.

Hymenolepis diminuta adults range from 10 to 60 mm in length and 3 to 4 mm wide without hooks on the scolex.

Ova:

R. nana: 40 – 60 µm oval with 2 membranes and 3 pairs of polar filaments arising from the inner membrane (photo, right).

Hymenolepis diminuta: 54 – 85 µm, yellowish and spherical.

Public Health Significance:  R. nana and H. diminuta are documented zoonotic parasites.