The Trematodes, or Fluke-worms

The trematodes or fluke-worms, though allied to the tape-worms, differ in many important characters. In the mature condition, like the latter, they are solid worms or are devoid of a body cavity or coelum, and are with rare exceptions hermaphroditic. They are, however, never compound, but simple or consist of single individuals, and are provided with a mouth and alimentary canal, but this is closed or is without an anal aperture. They have a water vascular system, communicating with the exterior by a pore at the posterior extremity of the body. They are commonly of flat, elliptical shape, with a sucker-like mouth at the fore end, and with a second sucker situated ventrally near the middle.

The fluke-worms are remarkable for their successive transformations and course of life, and, like the tape-worms, they pass the different stages of their existence in different animals. A number of species have been described as infesting man, but most of them are, fortunately, of rare occurrence.

DISTOMUM HEPATICUM.—SYNONYMS: Fasciola hepatica; Liver-fluke.

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.

TREATMENT.—As regards the treatment, we can say almost nothing. In the destructive disease of rot in sheep there are no known means to expel the parasites from the liver. If present in man, as they occur but few in number, we may hope for their spontaneous expulsion in due time without leaving any serious result. As a means of prophylaxis persons should carefully avoid salads prepared from subaquatic vegetables, like cress, which may harbor little fresh-water snails.

DISTOMUM HETEROPHYES.—This is a small species, about half a line long, with the fore part of the body covered with minute spines, and having a large, nearly central, ventral disk. It has been but once observed, and was reported by Bilharz, in Cairo, as having been found, in the post-mortem examination of a boy, in the small intestine, in which it existed in hundreds.

DISTOMUM CRASSUM.—This is the largest of the fluke-worms infesting man, and measures from one to three inches in length. It is elliptical, comparatively thick, and smooth. The two suckers have nearly the same relative size and position as in the D. hepaticum. It inhabits the duodenum, and has been observed a number of times infesting inhabitants of China and India.

DISTOMUM RINGERI.—A species by this name, about half an inch long, has recently been described by Cobbold as infesting the lungs of people in Formosa and China.

DISTOMUM OPHTHALMOBIUM.—A minute species, described under this name, has been detected several times in the human eye.

BILHARZIA HÆMATOBIA.—SYNONYM: Distomum hæmatobium.

As a human parasite this is the most important of the fluke-worms, being the most common and dangerous. It is apparently restricted to Africa and Arabia, and is especially frequent in Egypt, Abyssinia, the Cape of Good Hope, and Natal. So far as known, it is peculiar to man and monkeys, and inhabits the veins, especially those of the portal system, and it lives on the blood.

The blood fluke-worm is remarkable among its kind in having the sexes distinct. The female is slender, cylindrical, and tapering toward the ends, looking more like an ordinary thread-worm than a fluke-worm, and is about three-fourths of an inch long. The male is about half an inch long, but wider than the female, which it partially embraces at maturity by doubling upon it laterally.

This parasite, of the same essential nature as the more ordinary fluke-worms, is most probably introduced in the juvenile condition into the stomach by drinking unfiltered standing waters, and perhaps also by eating vegetables which grow in wet places and upon which the young fluke-worms may be encysted. From the stomach the worms gain access to the portal venous system, within which they undergo development to sexual maturity. The worms, proportioned to their number, occasion more or less sudden and dangerous hæmaturia. According to Bilharz, who first discovered the parasite, it also induces inflammation of the ureters, bladder, and rectum, accompanied with ulceration and incrustations and concretions in the same, due to the abundant deposit of eggs in the mucous membrane. The symptoms in the hæmaturia are obvious; all treatment fails, but the prophylaxis is evident.

AMPHISTOMUM HOMINIS.—The genus Amphistomum is distinguished from Distomum in having the ventral disk placed at the posterior extremity of the body.

A species has been recently described by Cobbold under the above name, and is reported as having been observed several times in natives of India. It is a red worm, about the fourth of an inch long, and inhabits the cæcum and ascending colon, in which it was found in hundreds together. The mucous membrane exhibited venous congestion and was marked with numerous red spots resembling leech-bites, produced by the parasites. One of the patients died of cholera.

We have too little information as to the symptoms induced by this parasite, and of its treatment, to say anything. It is probable that calomel, turpentine, and castor oil would be appropriate remedies.

Several other fluke-worms which have been reported as having been found in the human body are generally viewed with doubt as to their genuineness. Such are the Hexathyridium pinguicola, from a tumor of the ovary; the H. venarum, said to have been found in the blood and in the sputum of hæmoptysis; and the Tetrastomum renale, said to have been found in the urine.