Taenia expansa Sheep and ox Intestine
Taenia fimbriata Sheep Liver
Taenia denticulata Cattle Intestine
Taenia alba Cattle Intestine
Taenia perfoliata Solipeds Intestine
Taenia mamillana Solipeds Intestine
Taenia echinococcus Dog Intestine
LARVAL FORMS
Name Host
Cysticercus bovis Cattle
Cysticercus cellulosa Swine and man
Cysticercus tennicollis Cattle, sheep and swine
Coenurus cerebralis Cattle and sheep
Echinococcus polymorphus Cattle, sheep, swine and man
The adult tapeworms Taeniae saginata and soleum, of which the Cysticerci bovis and cellulosa are the larvae forms, occur in man. The larvae are present in meat and pork, and this form of parasitism is termed beef measles in cattle and pork measles in hogs. Man becomes host for these two forms of tapeworms through eating measly pork or beef that is not properly cooked.
The dog is the host for Taeniae marginala, coenurus and echinococcus. The larvae forms of these taeniae are the Cysticercus tennicollis, Coenurus cerebralis and Echinococcus polymorphus. C. tennicollis is a parasite of the serous or lining membranes of the body cavities. It is not of great economic importance. C. cerebralis is a parasite of the brain of sheep, and may cause a heavy death rate in flocks that are infested with it. E. polymorphus is a parasite of the liver, but it may occur in other organs.
THE THORN-HEADED WORM OR ACANTHOCEPHALE.—This parasite requires a secondary host. In this case a particular species of the May-beetle larva or white grub that is commonly found about manure piles and in clover pastures is the host. The hog eats a white grub that is host for the larval form. The digestive juices free the larva, it then becomes attached to the intestinal mucous membrane and develops into the adult thorn-headed worm (Fig. 74). This parasite is characterized by a hooked proboscis or thorn at its anterior extremity, and the absence of a distinct digestive tract. The male is much smaller than the female. The eggs are passed out of the intestine with the faeces.
[Illustration: FIG. 74.—Thorn-headed worms.]
THE ROUND-WORMS OR NEMATOIDS.—Round-worms are very common parasites of domestic animals (Fig. 75). This group of worms is characterized by their cylindrical form, the presence of a true digestive canal and the separation into two sexes, male and female. The life history is more simple than in the flat worms. Intermediate hosts are not required for the development of the common forms. The eggs and embryos are deposited by the female in the intestinal tract, air passages, or excretory ducts of the kidneys of the host. Development may be completed here, or the eggs and embryos are passed off with the body excretions. They may live for a short time outside the animal body, or undergo certain development and again infest a host of the same species from which they came, through the water, grass and fodder that the animal may take into its digestive tract.
[Illustration: FIG. 75.—Large round-worm in intestine of hog.]