Hymenolepis diminuta lives in the intestine of rats—Mus decumanus (the sewer rat), Mus rattus (the black rat), and Mus alexandrinus, rarely in mice; it is occasionally also found in human beings.
Weinland described it from specimens collected by Dr. E. Palmer in 1842, in Boston, from a child aged 19 months, as T. flavopunctata. A second case relating to a three year old child, from Philadelphia, was only reported in 1889 by Leidy; a third case was simultaneously reported of a two year old girl in Varese (T. varesina); and Grassi described another case relating to a twelve year old girl from Catania (Sicily). Sonsino and Previtera reported the same species in Italy, Zschokke in France, Lutz and Magalhães in South America, and Packard in North America: a total of twelve cases, five from America, the rest from Europe (Ransom).
Fig. 229.—Hymenolepis diminuta: two proglottids showing testes (3), ovary and vagina. Slightly enlarged. (After Grassi.)
Fig. 230.—Hymenolepis diminuta: egg from man. (After Bizzozero.)
According to Grassi and Rovelli the larval stage lives in a small moth (Asopia farinalis), as well as in its larva, in an orthopteron (Anisolabis annulipes), and in coleoptera (Acis spinosa and Scaurus striatus). Experimental infections have been successful on rats as well as on human beings. In America other species of insects may be the intermediary hosts.