. Handbook of medical entomology. Insect pests; Insects as carriers of disease; Medical parasitology. 176 Arthropods as Essential Hosts of Pathogenic Organisms. 114. Dipylidium caninum. Rostrum evaginated and invaginated. After Blanchard. In 1869, Melnikoff found in a dog louse, Trichodectes canis, some peculiar bodies which Leuckart identified as the larval form of this tapeworm. The worm is, however, much more common in dogs and cats than is the skin para- site, and hence it appears that the Trichodectes could not be the only intermediate host. In 1888, Grassi found that it could also develo
. Handbook of medical entomology. Insect pests; Insects as carriers of disease; Medical parasitology. 176 Arthropods as Essential Hosts of Pathogenic Organisms. 114. Dipylidium caninum. Rostrum evaginated and invaginated. After Blanchard. In 1869, Melnikoff found in a dog louse, Trichodectes canis, some peculiar bodies which Leuckart identified as the larval form of this tapeworm. The worm is, however, much more common in dogs and cats than is the skin para- site, and hence it appears that the Trichodectes could not be the only intermediate host. In 1888, Grassi found that it could also develop in the cat and dog fleas, Ctenocephalus felis and C. canis, and in the human flea, Pulex irritans. The eggs, scattered among the hairs of the dog or cat, are ingested by the insect host and in its body cavity they develop into pyriform bodies, about 3ooix in length, almost entirely destitute of a bladder, but in the immature stage provided with a caudal appendage (fig. 115). Within the pear-shaped body (fig. 116) are the invaginated head and suckers of the future tapeworm. This larval form is known as a cysticercoid, in contradis- tinction to the bladder-like cysticercus of many other cestodes. It is often referred to in liter- attire as Cryptocystis trichodectis Villot. As many as fifty of the cysticercoids have been found in the body cavity of a single flea. When the dog takes up an infested flea or louse, by biting itself, or when the cat licks them up, the larvffi quickly develop into tapeworms, reaching sexual maturity in about twenty days in the intestine of their host. Puppies and kittens are quickly infested when suckling a flea-infested mother, the developing worms having been found in the intestines of puppies not more than five or six days old. Infestation of human beings occurs only through accidental ingestion of an infested flea. It is natural that such cases should occur largely in children, where they may come about in 116. Dipylidium caninum. - .^- ^ . ^ Cyst
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