DISTOMATOSIS—LIVER FLUKE DISEASE—LIVER ROT.
In France the name of distomatosis has been given to a disease caused by the presence of distomata in the bile ducts. It is the “liver rot” of England, the Eberfäule of Germany, and is produced by the growth in the biliary ducts of oxen, sheep, and goats of two species of distomata, viz., the Distoma hepaticum or Fasciola hepatica, and the Distoma lanceolatum.
Fig. 142.—Fasciola hepatica. A, young; B, adult parasite. (After Railliet.)
In 1875 Zundel established the causative relation between the presence of distomata in the liver and the development of progressive fatal cachexia in most of the animals affected. This opinion was emphasised by the works of Leuckart and Thomas on the development of distomata, and at the present day the parasitic theory is accepted as beyond question.
Fasciola hepatica (Distoma hepaticum).—The common liver fluke of cattle, sheep, swine, etc.
Life history. The adult parasite, instead of producing young similar to itself and capable of developing directly into adults in cattle, produces eggs which develop into organisms totally different from the adult form, living a parasitic life in other animals. In scientific language, the parasite is subject to an alternation of generations, together with a change of hosts. The following summary of the life history will make this point clear:—
(a) The adult hermaphroditic worm (Figs. 144 and 145) fertilises itself (although a cross fertilisation of two individuals is not impossible) in the biliary passages of the liver, and produces a large number of eggs.
Fig. 143.—Eggs of Fasciola hepatica. A, from the bile duct; B, embryonic; C, after opening. (After Railliet.)