Cestode

“ Unlike the ordinary tapeworms, the segments of the broad tapeworm do not individually separate so as to become independent organisms, a circumstance which is highly favorable to the bearer. Its remarkable breadth, and the extremely numerous and closely-packed proglottides, impart a sufficiently distinctive character; but this parasite may be more fully characterised as the largest human cestode at present known, attaining a length of more than twenty-five feet, and sometimes measuring nearly an inch in breadth ”

“ Bothriocephalus cristatus, Davaine.—This cestode measures between nine and ten feet in length, and is characterised by the presence of two remarkable prominences, together forming a sort of rostellum or crest which is covered by numerous minute papillæ. The full-grown segments are less than half an inch in breadth; the body of the parasite being narrower than that of the broad species. The original description of the parasite by Davaine is based on two specimens, one of which, quite perfect, was obtained from a child five years old, under Dr Féréol’s care at Paris. ”

“ Tænia mediocanellata, Küchenmeister.—This cestode is frequently spoken of as the unarmed or beef tapeworm. In general appearance it is very similar to the armed form. It is, however, a larger and broader animal, being at the same time rather stouter. It varies usually from fifteen to twenty-three feet in length, but specimens have been described as attaining thirty feet. It is called the unarmed tapeworm in consequence of the absence of any coronet of hooks on the head; and consequently, also, from there being no prominent rostellum or proboscis. ”

“ When the infection has been intense, and the body is crowded with numerous oncospheres, acute feverish symptoms, are induced, to which the infected animals usually succumb (“acute cestode tuberculosis”) ; while in other cases the alterations in the organs attacked—as the liver in mice and the brain in sheep—may cause death.
Sooner or later the oncospheres of tapeworms come to rest, and are first transformed into a bladder, which may be round or oval according to the species. ”

“ Various tapeworm or cestode infections are contracted by eating meat containing the parasite. Particular species of tapeworm usually infest the flesh of specific hosts, as Tenia saginata in the beef and Tenia solium in the hog. The dwarf tapeworm, Hymenolepis nana, develops in rats, and the human infections with this parasite occasionally observed are probably caused by contamination of food by these animals. ”

“ If these are carefully sectioned there may usually be found at the center the remains of certain cestode larvæ whose presence in the oyster caused it to deposit the nacreous layers that make up the pearl. Other parasites cause similar growths in various shellfish. The great enlargements of the arms or legs or other parts of the body seen in patients affected with elephantiasis is an abnormal growth due to the presence of the parasitic filaræ in some of the lymph-glands where they have come to rest. ”

“ Any one of numerous species of cestode worms belonging to Tænia and many allied genera. The body is long, flat, and composed of numerous segments or proglottids varying in shape, those toward the end of the body being much larger and longer than the anterior ones, and containing the fully developed sexual organs. The head is small, destitute of a mouth, but furnished with two or more suckers (which vary greatly in shape in different genera) , and sometimes, also, with hooks for adhesion to the walls of the intestines of the animals in which they are parasitic. ”

“ Tænia solium, Linneus.—This cestode was formerly known as the common tapeworm, but in England it is of far less frequent occurrence than the beef tapeworm. In contradistinction it is best to speak of it as the pork tapeworm. Though only one specimen is usually present, the bearer may entertain several worms of this species at one and the same time. The parasite has been known to science from the earliest times, though possibly not earlier than the measles, or Cysticerci, from which it originates. Hippocrates, Pliny, and Aristotle describe the full-grown worm ”

“ Stoerk and Haendel are inclined to think that this species, unlike other Cestodes parasitic in man and domestic animals, needs no intermediate host for its development, and that the larval forms (cysticercoid) live in the same host as the adults. The diagnosis is based on the demonstration of ova in the stools. As far as expulsion of this Cestode is concerned, santonin, kamala, kousso flowers and thymol appear to have no effect of importance ”

“ In Pruner’s case, which is by no means unique, we have seen that two distinct species of cestode may coexist in the human bearer. It is quite possible that some one may yet have the good fortune to detect the beef tapeworm, the pork tapeworm, and the mutton tapeworm, all together in one and the same host.
On five separate occasions I have detected measles in “joints” of otherwise excellent and healthy mutton brought to my own table, and supplied by the family butcher. On several other occasions I have had these parasites brought under my notice ”

“ The organs most often affected are liver and lungs. The adult tape-worm (T. echinococcus) is found in the intestine of the dog, jackal, and wolf, occurring in considerable numbers between the villi. Its length (fig. 3, A) is at most 5 mm. and it consists of only three or four segments; the head has four suckers and a double circlet of hooks.
Pathological Effects.
The pathological effects of Cestodes fall naturally into two categories— (1) those due to the adult worm, and (2) those due to the larvæ or bladder worms. ”

“ The proglottides containing the eggs pass out of the final host along with the faeces and enter the intermediate host with the food. The larvae hatch, and boring their way into the blood-vessels, are carried by the circulation to various internal organs. Here they usually become "bladder-worms," and develop the "head" of the future sexual form. Then, if, as is usually the case, the intermediate host is preyed upon by the final host, the larval Cestodes enter the alimentary canal of the latter. The head of the larva alone survives digestion, and from it the mature worm is formed. ”

“ It must be obvious that in all cases where the intermediate host can be captured and destroyed, the life-cycle of the parasite can be broken and interrupted, and if thus broken, there is an end to the further propagation of the species. The knowledge that we have acquired by experimental research in this connection has already enabled us to set a limit upon the prevalence of certain well-known disorders, such as Trichinosis, Cestode-tuberculosis, and so forth. ”

“ After Busk.
Another cestode of general interest is the Tricuspidaria (Triænophorus) nodulosus, infesting many of our fresh-water fishes. It varies in length from one to two feet. The segmentation of the strobila is very indistinct, but the reproductive organs occur at regular intervals. All parts of the body are extremely contractile, especially the head. The tricuspid hooks support thin chitinous laminæ, which connect the two lateral horns of each hook to the central apophysis. ”

“ Every experimenter is more or less familiar with the cestode larvæ (C. pisiformis) found wandering in the abdominal cavity. These were regarded as flukes by Kuhn (Monostoma leporis) . I need hardly remark that the developmental and structural changes undergone by these Cysticerci during their residence within the rabbit have been exhaustively followed out and treated of by Leuckart. Without dwelling on this subject, I must in justice add that in this relation the special labors of Küchenmeister, Van Beneden, Haubner, Wagener, Röll, Eschricht, and Möller played no inconspicuous part. ”

“ In 20 species of fishes from the Great Lakes, 102 specimens, Dr. H. B. Ward found 95 specimens infected with parasites, securing 4000 trematodes, 2000 acanchocephala, 200 cestodes, and 200 nematodes. In the bowfin (Amia calva) , trematodes existed in enormous numbers.
Cestodes.—Cestode worms exist largely in marine fishes, the adults, according to Dr. Linton, being especially common in the spiral valve of the shark. It is said that one species of [Pg 345] human tape-worm (Bothriocephalus tænia) has been got from eating the flesh of the European tench (Tinca tinca) . ”

“ Life-histories.—The life-history of Cestodes consists of larval and adult stages, which are usually passed through in different hosts. The egg gives rise in the uterus to a six-hooked embryo, which reaches the first host in a variety of ways. It may hatch out as a ciliated organism (fig. 8, D) capable of living freely in water for at least a week (Bothriocephalus) , which then, if eaten by stickleback, throws off its ciliated envelope, and creeps by the aid of the hooks through the intestinal wall into the body-cavity of the fish. ”

“ All the cestodes have eggs, usually in great number, very well protected against external agents. They endure heat and cold, drought as well as humidity, resist by means of their envelopes the most violent chemical agents, preserve the faculty of germinating, we will not say for weeks, months, and years, but for centuries. When they first leave the egg, we see an embryo of an oval form, transparent, composed apparently of sarcode, contractile throughout all its extent, and in the middle of which we perceive six stylets arranged in pairs, and which at last move with great rapidity. ”

“ Neither the temperament nor the humours have any influence on parasites, and they are not more abundant in delicate individuals than in those who enjoy the most robust health. On the contrary, all wild animals harbour their parasitical worms, and the greater part of them have not lived long in captivity, before nematode and cestode worms completely disappear. It is only the imprisoned parasites which do not desert them. ”

“ An excretory system develops, opening at the base of the tail; nervous and muscular systems arise; and finally the rostellum and suckers become completely enclosed in the sac formed by the lateral extension of the “hind-body.” When swallowed by the final host such a “cysticercoid” larva evaginates its scolex, throws off its hooked vesicular tail, and begins to bud off proglottides at its free end (fig. 10) .
Such is the general history of Cestodes whose intermediate host is an Invertebrate. ”

“ Tænia solium: showing the head (h) with its suckers (s′) and crown of hooks (s) , the unjointed neck (n) , and a few of the succeeding joints (j) .
In other Tapeworms the cyst may be more complicated than that in the pig, as, for example, the form found in the sheep’s brain or the liver of the horse.
Of the other Cestode parasites mention should specially be made of those of Fishes; the vulgar notion that the parasites of these 118animals are dangerous to man has been shown to be entirely erroneous. ”

“ It is found, that in Egypt, a distoma is developed in the blood, and occasions a very severe malady, scarcely known to physicians. In Iceland, a cestode causes the death of a third part of the population. Worms develop themselves in the eye, and may even cause blindness; the Cœnurus of the sheep causes giddiness, and becomes fatal to the animal which harbours it. The chlorosis observed in Egypt and Brazil must, it appears, be attributed to a considerable development of a nematode worm, which lives in the small intestines, and which naturalists know under the name of Dochmius duodenalis ”

“ It is particularly to this last-named investigator that helminthology is indebted more than to any other author. He followed the gradual metamorphosis from oncospheres to cystic worms in all its details.
In view of all the researches that were made, and which are too numerous to mention individually, the idea that bladder-worms are abnormal or only incidental forms had to be abandoned. Everything pointed to the fact that in all cestodes the development is divided between two kinds of animals; in one—the host, the adult tapeworm is found ”

“ In a number of species it has been possible to determine fairly accurately the average daily growth; for instance, in Dibothriocephalus latus the daily growth is 8 cm., in Tænia saginata 7 cm., etc.
The history of the development of the Cestodes demonstrates that persons and beasts harbouring larval tapeworms have become infected by having swallowed the oncospheres of the species of tapeworm to which they belong. ”

“ As the mature tapeworm frequently finds the conditions suitable for its development in only one species of host, or in species nearly related, and perishes when artificially introduced into other hosts, experiment has taught us that to succeed in cultivating the oncospheres certain species of animals are necessary. Thus we are aware that the oncospheres of Tænia solium, which lives in the intestine of man, develop only in the pig, and only quite exceptionally develop into the stage characteristic of all Cestodes—the cysticercus in the wide sense of the word—in a few other mammals. ”

“ The same porpoise yielded the flukes already described (D. Campula) . As afterwards remarked in my treatise on the ‘Entozoa’ (1864) , four of the tapeworms measured, respectively, from 7′ to 10′ in length, the fifth example being relatively small (18′′ only) . For a full description of the worm I must refer either to the Linnean ‘Transactions’ or to my introductory volume whence the figures here given are taken. Five of the finest examples of this remarkable cestode have been added to the small collection of entozoa which I prepared for the Museum of the Middlesex Hospital Medical College. ”