Tapeworm

“ There is almost always an alternation of hosts, the larval tapeworm living in a so-called intermediate host, and the adult in a final host. Of the domestic animals the dog is the most frequently attacked. At least ten different species of tapeworms have been found in the dog. The intermediate hosts of these dog tapeworms include rabbits, sheep, mice, etc. Some of the domestic fowl, [Pg 140] ducks, geese and chickens, for instance, are also infested by tapeworms, and the intermediate hosts in these cases are usually insects or small aquatic crustaceans like the familiar Cyclops. ”

“ The larvæ (see Cysticercus) live in the flesh of various creatures, and when swallowed by another animal of the right species develop into the mature tapeworm in its intestine. See Illustration in Appendix.
Three species are common parasites of man: the pork tapeworm (Tænia solium) , the larva of which is found in pork; the beef tapeworm (T. mediocanellata) , the larva of which lives in the flesh of young cattle; and the broad tapeworm (Bothriocephalus latus) which is found chiefly in the inhabitants of the mountainous regions of Europe and Asia. ”

“ The tapeworm is a flatworm which has lost most of its organs on account of its parasitic life. Its egg is picked up by an herbivorous animal when grazing. The embryo undergoes only partial development in the body of the herbivorous animal, e.g. an ox. The next stage will not develop until the beef is eaten by a carnivorous animal, to whose food canal it attaches itself and soon develops a long chain of segments called a “tape.” ”

“ The same host does not always harbour the same worms in the different regions of the globe which it inhabits. This relates both to the parasites of man, and to those of the domestic animals. Thus the large tapeworm of man, which naturalists call Bothriocephalus, is found only in Russia, Poland, and Switzerland. A small tape-worm, Tænia nana, is observed nowhere except in Abyssinia ”

“ Trace the history of a tapeworm from the egg to the adult. At what stage are they most likely to be destroyed? What provision is there for this? What advantages are there to the host in the fact that a tapeworm's egg cannot develop in the original host? What advantages to the parasite? What organs has a parasite lost, if it ever had them? How does it succeed without them? What connection is there between parasitism and degeneration? Can you decide which is cause and which is effect? If so, which is? Why do worms so easily become parasitic? What advantages are there in becoming a parasite? ”

“ Last summer I heard a plug-hatted faker delivering a lecture to a street crowd, in which he said that every mother’s son or daughter of them who didn’t have the rosy cheek, the sparkling eye and buoyancy of youth might be sure that a tapeworm of monstrous size was, “like a worm in the bud,” feeding on their “damask cheeks.” To prove his assertion and lend terror to his tale, he held aloft a glass jar containing one of the monsters that had been driven from its feast on the vitals of its victim by his never-failing remedy. ”

“ Cause.—A dog eating raw flesh of sheep or cattle infested with the larva of the Tapeworm or Gid, Sturdy, or Water Balls. (See Gid in Sheep.)
Symptoms.—Tapeworms in dogs are numerous. It must be borne in mind that an animal is not free from them until the Tapeworm’s head, apparently the most insignificant part, has passed from the intestines. So long as the head remains attached to the wall of the bowels by its hooklets it will develop fresh eggs, producing segments which are passed and prove the means of scattering the parasites. ”

“ A model of the anterior end of the common Tapeworm shows the four suckers and the crown of hooks; the unjointed neck is followed by the joints (proglottids) , which increase in size the farther they are from the neck. Several entire specimens of Tænia follow, showing the size of the whole worm and the form of its joints. The structure of the body is shown in the models of two joints. The growth and development of the Tapeworm is dependent on a migration or a change of the hosts which it inhabits in the various stages of its life ”

“ Sometimes the existence of the tapeworm in man is restricted to the alimentary tract and the symptoms vary from trivial to severe, but sometimes (Tenia solium) the larval stage of the tapeworm invades the tissues and becomes encysted in various organs (brain, eye, etc.) , where, as in the case of cerebral infection, it may result fatally. The encysted larva of Tenia solium [p.83] was at one time regarded as an independent animal species and named Cysticercus cellulosae. The condition known as "measly pork" is produced by the occurrence of this encysted parasite. ”

“ By infecting man or animals who ingest it. It is thus, for example, that man, dog, or cat, becomes infected with the double-pored dog tapeworm, Dipylidium caninum. The cysticercoid stage [Pg 5] occurs in the dog louse, or in the dog or cat fleas, and by accidentally ingesting the infested insect the vertebrate becomes infested. Similarly, Hymenolepis diminuta, a common tapeworm of rats and mice, and occasional in man, undergoes part of its life cycle in various meal-infesting insects, and is accidentally taken up by its definitive host. ”

“ Fig. 140.—Portion of the liver of a lamb which died nine days after feeding with eggs of the marginate tapeworm (Tænia marginata) , with numerous “scars,” due to young parasites. (After Curtice.)
Life history. In tracing the life history it is best to begin with the egg, produced by the adult tapeworm in the intestine of dogs. These eggs, containing a six-hooked embryo, escape from the dog with the excrements, and are scattered on the ground, either singly or confined in the escaping segments of the tapeworm. ”

“ If any argument were necessary to show how desirable it is to furnish full descriptions of the commoner kinds of parasite, I could adduce numerous instances that have been brought under my notice where professional men and others have been entirely mistaken as to the essential nature of their parasitic finds. Thus, I have known an instance where a great authority on the diseases of dogs has persisted in asserting for the free proglottides of a tapeworm a nematode origin; and, in like manner, human tapeworm-segments have frequently been mistaken for independent fluke parasites. ”

“ Tænia tenella, Cobbold.—I have long been acquainted with the fact that there is a comparatively small human tapeworm which cannot be referred to either of the foregoing species. In the absence of experimental proof, I incline to the belief that the worm in question owes its existence to measly mutton. The sheep harbours an armed Cysticercus (C. ovis) , which I regard as the scolex of Tænia tenella. The specific name (tenella) was originally applied by Pruner to a cestode six feet in length, which he found associated with a larger tapeworm. This latter he called Tænia lata. ”

“ The worms are found attached to the walls of the stomach and small intestines.
The tapeworms of marsupials are more numerous than flukes. Thus, we have Rudolphi’s Tænia festiva, eight to ten inches in length, occupying the gall-bladder and hepatic duct of Macropus giganteus. Dr Bancroft’s collection contains two almost perfect examples of a tapeworm which he procured from a small streaked kangaroo (Halmaturus Derbyanus) . These I have identified as T. festiva. In this worm the reproductive papillæ, not hitherto observed, are biserially arranged. ”

“ Some people, including not a few of the profession, make light of the occurrence of tapeworm, and I have seen many patients who had been told by their usual medical advisers that the presence of the worms was of little consequence. ”

“ 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. ”

“ The olulanised mouse is thus an intermediate host. Rats and mice also play the part of intermediary bearers in the case of two other species of entozoa, namely, Trichina spiralis and Tænia crassicollis, the tænioid scolex or larval condition of the cat’s tapeworm being familiarly known as Cysticercus fasciolaris. This sexually-immature tapeworm infests many other rodents, especially the voles (Arvicolidæ) . In regard to Trichinæ it must not be forgotten that their presence in rats is not uncommon in some parts of Europe ”

“ Respecting the organisation of this worm I may observe that the mature joints have a more complicated uterine organ than obtains in Tænia solium, presenting nearly double the number of lateral branches. They are more closely packed, running outwardly in an almost parallel manner. The first sexually mature proglottis occurs at about the 450th joint, but whereas, in the pork tapeworm, only some 200 subsequent segments share this perfect character in the beef tapeworm, according to Leuckart, as many as 360 or even 400 mature joint may be present. The joints are very liable to form monstrosities ”

“ In regard to Hymenolepis murina alone, it is known that the introduction of the oncospheres into those species of animals which harbour the adult tapeworm leads to the formation of the latter after the development of a larval stage in the intestinal wall; nevertheless, only young animals (rats) are capable of infection, for a previous infection, or the presence of mature tapeworms in the intestine, appears to produce a kind of immunity. ”

“ 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 ”

“ 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 ”

“ The tapeworm most frequently found in man in Western Europe is the Taenia solium, which is constant wherever pork is consumed, and is more common in parts where raw or imperfectly cooked pork is eaten. In North Germany the mature tapeworm was found on post-mortem examination once in every 200 bodies examined, while its embryo, the Cysticercus cellulosae, was found in 1 in every 76 bodies, In France, Great Britain and the United States the prevalence is not so great. ”

“ The mature pork tapeworm is about ten feet long, although the eggs, seen in the pork flesh, giving it its name of "measly," are only about a thousandth of an inch in diameter. The fish tapeworm, when mature, measures about twenty-five feet in length, while the beef tapeworm is about the same length. These worms can develop only in the bodies of the animals named, and find their way into the human body only through the medium of imperfectly cooked meat. ”

“ I may here mention that tapeworms do not breed in a dog, but the eggs or larvæ must pass out of him and be swallowed by some other living creature, who is called the intermediate host. Here they develop into cysts or bladder-worms, and if these in their turn are swallowed by a dog they develop into a tapeworm, and so the cycle is completed. ”

“ The developing eggs are passed off with wastes from the intestine of man. The pig, an animal with dirty habits, may take in the worm embryos with its food. The worm develops within the intestine of the pig, but soon makes its way into the muscle or other tissues. It is here known as a bladderworm. If man eats raw or undercooked pork containing these worms, he may become a host for the tapeworm. Thus during its complete life history it has two hosts. Another common tapeworm parasitic on man lives part of its life as an embryo within the muscles of cattle. ”

“ This has been elaborated still further by van Beneden, v. Siebold and Leuckart, and until a few years ago all authorities adopted his views. According to this view, the tapeworm is composed of numerous individuals, something like a polyp colony, and, in addition to the proglottids—the sexual individuals which are usually present in large numbers—there is ONE individual of different structure, the scolex, which not only fastens the entire colony to the intestine, but actually produces this colony from itself, and therefore is present earlier than the proglottids. ”

“ There are numerous species of them, all of which live in the bodies of vertebrate animals. In the adult or fully developed stage the tapeworms live in the alimentary canal, holding on to its inner surface by hook-like clinging organs and being nourished by the already digested food by which they are bathed. In the young or larval stage tapeworms live in other parts of the body of the host, and usually, indeed, in other hosts not of the same species as the host of the adult worm. ”