A system of practical medicine. By American authors. Vol. 2

by Unknown

This species, the common liver-fluke, occasionally occurs in the human body, but is especially frequent in the sheep and other ruminating animals, as the ox, goat, and deer, and it likewise occurs in the horse, hog, and some other animals. It usually inhabits the liver, occupying the bile-ducts, but is also sometimes found in the portal and other veins and in the intestine, and more rarely in abscesses beneath the skin. It is the cause of the affection in sheep called rot, of which many thousands die annually.

The liver-fluke is a flat, tongue-shaped, brownish worm about an inch long and about half as wide. It is invested with minute scale-like spines. The head end is somewhat prolonged, and terminates in a small oral sucker, a short distance behind which is a small ventral sucker. The intestine is forked and much branched. The genital aperture is situated between the oral and ventral suckers. The commonly yellowish eggs are numerous and large, oval, and measure about 0.135 mm. long.

The common liver-fluke frequently occurs in large numbers, even hundreds, in the liver of the sheep, obstructing the bile-ducts and occasioning more or less destruction of the organ. The eggs pass off with the bile into the intestine, and are discharged with the excrement. In water the eggs are hatched, and deliver a ciliated and freely-swimming embryo. This in favorable positions, such as marshy pastures, obtains access to small fresh-water snails and penetrates to the interior of their body. Here the embryo sheds its ciliated integument and is transformed into a sporocyst. This is an elliptical pouch containing reproductive bodies, which become developed into individuals of more elongated form than the sporocyst, provided with a mouth and stomach, and named redias, or nurses. The nurse penetrates to the liver of the snail, and there develops within itself new forms called cercarias, which resemble the parent fluke-worm, but are provided with a long, powerful tail and have no apparent generative apparatus. The cercaria escapes through an aperture of the nurse, and makes its way out of the snail into the water, where it swims about actively by means of the tail, much in the manner of a tadpole. The cercaria after a time fixes itself to a submerged plant, becomes encysted, shakes off its tail, and remains in a quiescent state. If in this condition, in the feeding of sheep or other animals, the tailless cercaria or incipient fluke-worm is transferred to the stomach, it makes its way to the liver, and there grows and is developed into the sexually mature worm.

Recently it has been ascertained both in England and Germany that the juvenile state of the fluke-worm is passed especially in the little fresh-water snail Lymneus truncatulus. As, however, the common liver-fluke occurs in America, while the last-named species of Lymneus does not, it is rendered probable that the juvenile condition of the parasite also occurs in other species of snails. Incidentally, the writer may here mention that he has found certain of our smallest fresh-water snails, such as Planorbis parvus, frequenting meadows in the vicinity of our rivers and creeks, swarming with nurses of several different species of fluke-worms.

Notwithstanding the frequency of the common liver-fluke in the sheep and other domestic animals, its occurrence has been rare in man, and in all the cases reported it has been few in number, either single or from two to half a dozen. In man it has been found to occupy the bile-ducts, the portal vein, and abscesses beneath the skin.

DISTOMUM LANCEOLATUM.—SYNONYM: Smaller Liver-fluke.

This species, much smaller than the preceding, is of lanceolate form, acute behind, smooth, and about a third of an inch long. Its suckers are moderately large, and the bifurcate intestine is unbranched. It infests the liver of the sheep and ox and some other animals, and not unfrequently is found in association with the former species. It usually does not occur in such great numbers together as in the latter; from which and other circumstances, as the smaller size and smooth investment, it does not produce the same serious results. Its continuous history remains unknown, though it is probable that its course is similar to that of the common liver-fluke. Several cases are reported of its occurrence as a parasite in man.

DISTOMUM SINENSE.—Under this head Cobbold has recently described a species somewhat larger than the D. lanceolatum. It occurs in the liver of Chinese.

DISTOMUM CONJUNCTUM.—Another species described by Cobbold under this name, originally found in the liver of an American fox, has also been detected in man. The worm is about one-fourth of an inch long.

SYMPTOMS.—Cases of fluke-worms in the human liver have occurred so rarely that we are not prepared to indicate with certainty what may be the nature of the peculiar symptoms. If the parasites were numerous, they would give rise to more or less obstruction of the bile-ducts, with accumulation of bile, accompanied with jaundice and other symptoms usually attendant on functional disturbance of the liver. As in sheep, they would occasion dilatation of the bile-ducts, catarrhal inflammation, incrustation with biliary matters, hyperplasia of the surrounding tissues, and more or less disorganization and atrophy of the secretory structure.