Parasitic worm

“ It is as lowly organized as the simplest of parasitic worms, and it is only by a study of its development that we learn it is not a worm at all, but a gasteropod mollusk, which has become degraded or simplified to adapt it to a parasitic life. ”

“ Mention is made under Tapeworm of the worms of that species inhabiting the human body as parasites, and it will be convenient here to mention other parasitic varieties. The most common human parasite is the Ascaris lumbricoides or round worm, found chiefly in children and occupying the upper portion of the intestine. ”

“ The presence of these parasites finally exhausts the host, so that the sterile female bee dies prematurely.
41. Bee fungus.
As in the higher animals, bees are afflicted with parasitic worms which induce disease and sometimes death. The well-known hair worm, Gordius, is an insect parasite. The adult form is about the size of a slender knitting needle, and is seen in moist soil and in pools. It lays, according to Dr. Leidy, "millions of eggs connected together in long cords." The mi [Pg 47] croscopical, tadpole-shaped young penetrate into the bodies of insects frequenting damp localities. ”

“ The young marine naturalist, working on our coasts, will not be brought into intimate contact with parasitic worms to any large extent, yet we have said this little on parasitism to show that these degenerate creatures are not really devoid of interest, and that they will repay study whenever they are found. ”

“ When a species, owing to highly favourable circumstances, increases inordinately in numbers in a small tract, epidemics—at least, this seems generally to occur with our game animals—often ensue: and here we have a limiting check independent of the struggle for life. But even some of these so-called epidemics appear to be due to parasitic worms, which have from some cause, possibly in part through facility of diffusion amongst the crowded animals, been disproportionably favoured: and here comes in a sort of struggle between the parasite and its prey. ”

“ The same thing happens amongst quadrupeds. We have, for example, parasitic equine epizoötic outbreaks, and likewise non-helminthic equine epidemics (as in the case of the Egyptian horse plague of 1876) . The true nature of any epizoöty can only be determined by competent investigation. That was well shown in the grouse epidemic of 1872. In that epizoöty the greater number of the birds succumbed to the injuries produced by a nematode worm (Strongylus pergracilis, Fig. 73) , but, without doubt, the occasional presence of numerous tapeworms (Tænia calva) hastened the consequent fatality. ”

“ Parasitic worms of various kinds, though they often cause disease and death, are accepted and tolerated even by the most refined and luxurious, who risk infection rather than submit to the precaution of abstention from raw vegetables and fruits, or to the expenditure of trouble in cleansing those nests of infective germs. It is only within the last thirty or forty years that such cleanliness of body and of clothing and of house-fittings as will banish parasitic insects has become at all general. ”

“ Unless this effect, which results as a rule in the Red Grouse from excessive parasitism, is fully recognised, there will always be misunderstandings upon the moult of this bird, for almost every Grouse in the country is to some extent infested with parasitic worms, and there are years when irregularity of moult is the rule rather than the exception. ”

“ The immature and mature forms of tapeworms are parasites of vertebrate animals, but an invertebrate host is necessary for the completion of the life cycle of the fluke. The hog is the only specie of domestic animals that becomes a host for the thorn-headed worm. The round-worm is a very common parasite. ”

“ 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? ”

“ 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. ”

“ Parasitism is a phenomenon common in all the large groups of animals, though the parasites themselves are mostly invertebrates. There are parasitic Protozoa, worms, crustaceans, insects, and molluscs, and a few vertebrates.
Some parasites, like the fleas and lice, live on the surface of the body of the host. These are called external parasites. Others, as the tapeworms, live exclusively inside the body; such are called internal parasites. Again, some, as the bird-lice, which are external parasites feeding on the feathers of birds, spend their whole lifetime on the host ”

“ Here the worm, always lodged in the intestines, grows with extraordinary rapidity, and fulfils all the conditions of a true parasite. In a fertile soil it extends itself and produces young as long as it has any life, and in no group of the animal kingdom do we find any fecundity to be compared to that of this worm. Boerhaave described a broad tape-worm, three hundred ells in length. ”

“ How great a number of animal parasites exists may be gathered from the fact that all classes of animals are subject to them. Some of the larger groups, such as Sporozoa, Cestoda, Trematoda and Acanthocephala, consist entirely of parasitic species, and parasitism even occurs among the vertebrates (Myxine) . ”

“ A number of diseases in man and other animals are due to the presence of these Sporozoans, for they are all parasitic. Few if any animals are exempt from their attacks. They even attack other minute Protozoa. One hundred and fifty-seven species have been recorded as attacking insects, one hundred species attack birds, fifty-two reptiles, eighty crustaceans, twenty-two fish, and so through the list. Ten have been recorded as attacking man. In some instances the parasite is always present in the host and some hosts may harbor several different species of Sporozoa. ”

“ The first female which presents itself allows us to answer this question. It is not a parasitical worm, at least under this form, because each female contains only one or two eggs. Parasites have so few chances of arriving at their destination, that two young ones would not be sufficient. They must have hundreds or thousands, and then the chances are against them. This worm is evidently a Rhabditis, but is it that which lives in the earth, or an allied species? ”

“ The pathological changes in the brain are local reactions in response to the presence of eggs, and, although ectopic parasitism of the adult worms in the cerebral vessels has been suggested, up until now, no worm has ever been found in specimens of the human brain. ”

“ 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 ”

“ One of the most interesting methods of extension of infection, showing on what small circumstances infection may depend, is seen in the case of the hookworm disease, which causes such devastation in the Southern States. The organism which produces the disease, the Uncinaria, belongs to the more highly developed parasites, and is a small round worm one-third of an inch long. ”

“ Some years since, no one suspected that a parasite could live in any other animal than that in which it was discovered. All helminthologists, with few exceptions, looked upon worms in the interior of the body as formed without parents in the same organs which they occupy. Worms which are parasites of fish, had been seen a long time before this in the intestines of various birds: experiments had even been made to satisfy observers of the possibility of these creatures passing from one body to another ”

“ It is quite evident that the lives of many valuable animals are annually sacrificed by the neglect of hygienic arrangements. The palisade worm is chiefly destructive to young animals, and as Mr. Percivall has well remarked, these parasites are “commonly the cause of lingering and hidden disease, terminating in death,” without any suspicion on the part of the practitioner as to the nature of the malady. ”

“ Even our metropolitan scientific institutions, expressly raised for the purpose of diffusing useful knowledge, shrink from the revelations of parasitism. Dominated by the miserable conception which judges that the life-history of a worm cannot prove either interesting or instructive to their audiences, they let slip the acquisition of scientific data, a knowledge of which might enable them to combat successfully some of the most terrible evils to which human flesh, in common with that of animals, is heir. ”

“ Another species of thread-worm (Filaria lacrymalis) is occasionally found in the horse between the lids and eyeball. It is a comparatively small and harmless parasite, the males measuring 1/2′′ in length and the females 2/3′′. It also infests the ox. Both the large and small eye-worms are viviparous, and, not improbably, both of them are the means of conveying embryonic Filariæ into the circulation. Be this as it may, we owe to Dr Sonsino the discovery of hæmatozoa in an Egyptian horse. The larval worm was provisionally named by him Filaria sanguinis equi. ”

“ Minute Nematodes abound in moist soil, around the roots of plants, etc., and may easily be detected with the aid of a lens wriggling about amongst the particles of sand and earth. Of the animal parasites perhaps the most familiar is the "round worm" (Ascaris lumbricoides, Figs. 66 and 67) , which inhabits the alimentary canal of man; others are common in domesticated animals, as A. mystax in the cat and dog, and A. megalocephala in the horse and ox. They are also found living parasitically in plants (Fig. 77) , causing the formation of galls and other pathological growths ”

“ In fact, it becomes difficult to say where the line of parasitism should be drawn. I cannot, however, ignore all notice of the insect tormentors, whether strictly parasitic or not.
At least fifty different species have been regarded as playing the rôle of parasitism in man. ”

“ It appears that immersion in water, of the body of the person afflicted with the parasite, sometimes has the effect of inducing the creature to leave his human quarters, since Dr Lorimer states “that many people belonging to the bazaars in the vicinity of the lines, affected with the parasite, come, for the express purpose of extracting the worm, to the same tank where the men of the regiment bathe. The people so infested swim about in the water, with the worm hanging loose, drawing the limb quickly backwards and forwards, and from side to side, until the expulsion is affected.” ”

“ According to Looss, this is, however, not the case, but the species easily escapes notice on account of its small size. Looss found it in Alexandria twice in nine autopsies, and once in Cairo, and has recently stated that in man “it is not at all uncommon to meet with the parasite in cadavers, and the eggs of the worm in the stools of the patients.” Leiper records one case from Japan and one from China. The parasites occupy the middle third of the small intestine, and even when present in large numbers appear to be harmless. ”

“ The disease caused by infection with this parasite is usually termed dracontiasis and the parasite Dracunculus medinensis or the Guinea worm.
The geographical distribution includes India, Arabia, the West Coast of Africa and Brazil.
Life History.—The male has not surely been seen in man so that the pathological condition is entirely connected with the female worm. Almost invariably the female worm, which measures about two feet long by 1/12 inch broad, tends to wander down to the connective tissue structures of the lower extremity. ”

“ Development within the body of the mosquito will only take place when the parasite is taken into its body at this sexual stage.
The Cause of Malaria.—The study of the life history and habits of the Protozoa has resulted in the finding of many parasitic forms, and the consequent explanation of some kinds of disease. One parasitic protozoan like an amœba is called Plasmodium malariæ. ”

“ There is yet another Filarian worm, a pest to the poultry-yard, the Gape-worm, Sclerostoma syngamus. This parasite is widely distributed, and is invested with special interest, since it produces disease, and kills annually thousands of young chickens, pheasants, partridges, and many of the larger kinds of wild birds. The worms find their way into the windpipe or tracheæ, through the drinking water, while in the embryotic or cercarian stage of existence, and their increase is so rapid, the birds quickly die of suffocation. ”