Helminthology

HELMINTHOLOGY (from the Greek helmins—parasitic worm, and logos—word, science), the science that studies the world of parasitic worms and the diseases caused by them in humans, animals, or plants. In one of its aspects, helminthology is a branch of zoology; on the other hand, by studying the pathological processes that occur in the host organism under the influence of helminthic invasion, helminthology is a department of such disciplines as medicine, veterinary medicine, agronomy, and comparative pathology. History of Helminthology. The first information about parasitic worms, as far as can be judged from the most ancient historical monuments, came from medical sources. In the famous Ebers papyrus, dating back to 1550 B.C., there is information about human parasitic worms, in particular about the ascaris and the tapeworm. The greatest Egyptologists, who deciphered the hieroglyphs of this papyrus, found that it contains a whole series of instructions on how to treat helminthic diseases and how to kill parasitic worms in the human body. In the Bible of Moses (about 600 B.C.) there is a reference to parasitic worms, where the "fiery serpents" apparently should be considered filariae—Fullebornius medinensis (guinea worm). The cited symptoms of kidney and urinary tract diseases indicate the existence of Egyptian schistosomiasis, confirmation of which is found in the work of Ruffer, who, during a microscopic study of the kidneys of Egyptian mummies (1250–1000 B.C.), discovered schistosome eggs. Hippocrates (460–370 B.C.) introduced the terms helminthos and askaridos. He attached very serious importance to worms, spoke about the prevalence of ascarids in children, about the alleviation of the course of the disease after the expulsion of worms, etc. However, Hippocrates confused worms with insect larvae, earthworms, and even snakes. Hippocrates was aware of: 1) the symptoms of tapeworm diseases in children, 2) echinococcal diseases in humans and domestic animals, which he considered a special form of dropsy, 3) pinworms in humans, and he even knew about the migration of this parasite into the genital slit of women. Aristotle (384–342 B.C.) knew 3 types of worms: the ascaris, the taenia, and the pinworm; he also described the cysticercosis of pigs but did not suspect its animal nature. By "helminths," Aristotle meant worms and insect larvae. In the Roman period of the classical era, when the concept of "vermis" was introduced, under which everything "small, elongated, soft, and crawling" was understood, parasitic worms naturally fell into this category. The Middle Ages did not contribute anything new to helminthology. Scientific helminthology began to develop in the second half of the 18th century. The father of scientific systematics, Linnaeus, subdivided the entire animal world into 6 classes, with all invertebrates being included by him either in the class Insecta or in the class Vermes (worms). Linnaeus derived parasitic worms from free-living forms, catching the similarity of Fasciola hepatica with planarians, pinworms with free-living nematodes, and the broad tapeworm with the larva of the fish acanthocephalan. The St. Petersburg academician Pallas recognized elements of their further development in the eggs of parasitic worms and thus dealt a blow to the theory of spontaneous generation of worms, which, however, persisted for a very long time, finally disappearing only in the second half of the 19th century. The end of the 18th century and the very beginning of the 19th century are characterized by the work of a whole galaxy of major helminthologists (Müller, Goeze, Bloch, Zeder, Batsch), who created helminthological science. Goeze (1782) subdivides parasitic worms into round and flat, and Zeder (1800) establishes 5 classes for them: roundworms, acanthocephalans, flukes, tapeworms, and bladder worms, and by 1803 he registers 391 species of parasitic worms. The father of helminthology in general should in fairness be considered Karl Rudolphi (1771–1832), who in his Entozoorum synopsis (Berlin, 1819) provided a brilliant summary of all data on parasitic worms, of which he already counted 981 species and subdivided into 30 genera. His contemporary, the Viennese physician Bremser, author of the first work on medical helminthology—"Über lebende Würmer im lebenden Menschen" (Vienna, 1819; Russian edition—1839), is rightfully considered the founder of this discipline. In 1818, Bojanus discovered cercariae in mollusks, in which he recognized trematodes, without, however, understanding the meaning of their presence in mollusks; in 1831, Mehlis observed the hatching of a miracidium from a trematode egg. A huge achievement in the field of studying the development cycle of trematodes was the establishment by Steenstrup in 1842 of the phenomenon of alternation of generations, which was later experimentally (1857) proven by de Filippi and Pagenstecher. As for the development cycle of cestodes, it did not yield to deciphering for a long time, because the bladder forms of their larvae were either recognized as representatives of an independent class (Cystici) or considered pathological elements. Only from the middle of the 19th century, when helminthology entered the path of experiment, was the connection of the strobila with the corresponding bladder form established. The first experimenter was Küchenmeister (1851), who, by feeding a dog Cysticercus pisiformis, grew a Taenia pisiformis strobila in it; in 1854, Leuckart obtained the sexually mature form of this parasite in the intestine of a cat fed with Cysticercus fasciolaris, and in the following year, an experiment was conducted by Küchenmeister on a human with Cysticercus cellulosae, as a result of which the development cycle of Taenia solium was brilliantly revealed. In the middle of the 19th century, there was already a bright flourishing of helminthology in the major states of Western Europe: in Germany (Leipzig)—Leuckart's helminthological school, which produced the greatest representatives (Loos, Braun); in France—Dujardin, Davaine; in Austria—Diesing; in Belgium—Van Beneden; in England—Cobbold. However, the center of helminthological thought during this period was Leipzig, where all those wishing to join the helminthological discipline, which at that time did not have a clearly expressed applied direction, as it was cultivated on the basis of the Department of Zoology of the Faculty of Philosophy, flocked to Leuckart. By the end of the 19th and the beginning of the 20th century, the "encyclopedic" period of the development of helminthology ends and the process of its differentiation begins, which proceeds very differently in different countries: on the one hand, applied helminthology—medical and veterinary—develops at a rapid pace; on the other, general helminthology is fragmented into its constituent systematic elements: nematodology, trematodology, cestodology, and acanthocephalology; moreover, the volume of each of the above-mentioned departments of helminthology reaches such a large scale that a process of further differentiation occurs within these private helminthological disciplines: the study of cestodes of birds, trematodes of fish, nematodes of mammals, etc., is singled out. On the other hand, there is also differentiation along the lines of studying individual elements of helminthology as a zoological discipline: the study of anatomy, physiology, embryology, systematics, geography of parasitic worms, etc. History of Helminthology in the USSR. The birthplace of Russian helminthology is Dorpat (Yuryev). Here, in 1821, Academician E. I. Eichwald (1795–1876), who was at that time a private docent at Dorpat University, gave a special course on helminthology. This talented scientist laid the foundation for the helminthological collection of the St. Petersburg Medico-Surgical Academy. With Eichwald begins the encyclopedic period of the history of helminthology in Russia. The figures of this period were zoologists in the broadest sense of the word, who studied, among other things, parasitic worms. It is necessary to include here the brilliant Karl Ernst von Baer (1792–1876), a student of Dorpat University and an academician of the Russian Academy of Sciences, the founder of comparative embryology, who was also interested in helminthology: he described many trematodes, such as Nitzschia, Bucephalus, Aspidogaster, and some others. F. F. Brandt, who replaced Eichwald at the Medico-Surgical Academy and created fame for himself as the founder of the Zoological Museum of the Russian Academy of Sciences, which he transformed from the so-called Kunstkamera, wrote in collaboration with Ratzeburg the classic work "Medical Zoology," published in 1833. Not being a helminthologist, F. F. Brandt in this work highlighted the importance of parasitic worms for medicine. His successor to the chair of zoology at the Medico-Surgical Academy, E. K. Brandt (1839–91), was an expert in helminthology; he gave his zoology course the character of a parasitology course. E. K. Brandt released 2 works: "Animal Parasites of Man and Domestic Animals" (St. Petersburg, 1873, a reworking of Zürn's book) and "Animal Parasites of Domestic Mammals and Birds" (St. Petersburg, 1887). These books were destined to play the role of the main Russian manuals on veterinary and medical parasitology in general and helminthology in particular for several decades. While E. K. Brandt worked in St. Petersburg, helminthology was cultivated in Dorpat by one of the greatest helminthologists of our time, M. Braun. In 1871, at the Dorpat Veterinary Institute, Blumberg defended the first dissertation for the degree of Master of Veterinary Sciences on a helminthological topic—"Über Amphistomum conicum."

Having subsequently received the chair of pathological anatomy at the Kazan Veterinary Institute, he continued to work there very fruitfully, mainly in the field of veterinary Helminthology, writing a whole series of works and notes. For the sake of completeness, it is necessary to note that in the 1870s, Fedchenko, a student of Leuckart, also worked on Helminthology, having studied the development cycle of the Guinea worm, described the gnathostome, and provided a list of parasitic worms of humans found in Turkestan. In the same years (1868), the Russian zoologist Melnikov, subsequently a professor at Kazan University and the Veterinary Institute, studied the development cycle of Dipylidium caninum in the body of the dog louse in Leuckart's laboratory. Thus, from the time of Eichwald until the beginning of the 20th century, in Russia, strictly speaking, there were no specialist helminthologists (if one does not count Braun): there were many zoologists who were interested, among other things, in questions of Helminthology, but who did not devote themselves entirely to the study of this discipline. As a result, Russian Helminthology, having been born in Dorpat, was cultivated throughout the 19th century, mainly in two centers—in Dorpat and St. Petersburg. After the death of E. K. Brandt, the chair of zoology at the Medico-Surgical Academy was occupied in 1892 by N. A. Kholodkovsky, who developed his helminthological activity starting from 1894. In addition to a number of special works, he compiled the first 'Atlas of Human Worms' in our literature (St. Petersburg, 1898). Individual works on Helminthology came from the pen of the Moscow zoologist N. Zograf (the 80s), the Kharkov zoologist P. Stepanov (1873), the St. Petersburg zoologist Kessler (1868), and Academician V. I. Zalensky (a work on Amphilina, 1874). At the turn of the 19th and 20th centuries, temporary helminthological centers were created in Warsaw, Kharkov, and Novocherkassk, and the cultivation of Helminthology continued at the Military Medical Academy (by Kholodkovsky); from 1920, Moscow became the center for both veterinary and medical Helminthology in the USSR. Helminthology began to develop especially rapidly from 1917, when the first chair of parasitology in Russian higher schools opened at the Don Veterinary Institute, which adopted a sharply defined helminthological orientation. At the present time, there are dozens of institutions for both medical and veterinary Helminthology. The first institution for medical Helminthology was the Tropical Institute in Moscow, which organized a special helminthological department in 1921. Branches of helminthology. Being a multifaceted discipline, Helminthology naturally permeates the most diverse fields of both theoretical and applied knowledge. Helminthology can be divided into general, veterinary, agronomic, forestry, and medical. As a general biological discipline, Helminthology studies the world of parasitic worms from the most diverse points of view. In recent years, some new directions have emerged in helminthology: helminthogeography has been born, studying the distribution of parasitic worms in different regions of the globe and the causes on which this distribution depends; problems of helminthosociology have begun to be studied, and the study of helminthological communities, connected by the commonality of that physical-chemical environment which the juices and tissues of the host are for them, has begun; a special geohelminthological direction has appeared, i.e., the study of parasitic worms, regardless of their belonging to one class or another, irrespective of which host they localize in, but from the point of view of their connection with the geographical character of this or that locality, of these or those individual habitats. Thereby, this direction studies the helminthofauna of steppes, taiga, tundra, and deserts in the same way as an ornithologist or entomologist does, studying animals of various habitats accordingly. Veterinary Helminthology studies the parasitic worms of domestic animals and the diseases caused by them. Of particular interest to medicine are those chapters of veterinary Helminthology that study helminthozoonoses, i.e., worm diseases common to animals and humans. The scope of veterinary Helminthology is very large due to the fact that several hundred species of worms parasitize domestic mammals and birds. Agronomic Helminthology studies worm diseases of agricultural plants and their causative agents (wheat gall nematode, sugar beet nematode, potato nematode, etc.). Forestry Helminthology studies, on the one hand, worms parasitizing forest species, and on the other, parasites infesting the organisms of forest pests (bark beetles, butterflies, etc.). Thus, the objects of forestry helminthology are partly not enemies, but friends of man, helping the latter to fight harmful insects of forest species. Scope and content of medical Helminthology. The task of medical Helminthology is the comprehensive study of both the worms infesting the human organism and the diseases caused by them. Only with such a comprehensive illumination of issues does this discipline acquire a finished integrity and importance for medicine. A physician needs to be familiar with helminthological diagnostics; it is necessary to determine the form of the parasite with which his practice has confronted him (antemortem or postmortem diagnostics); for this, the physician must resort to the help of the systematics of parasitic worms, which at the present time is entirely based on morphology; in other words, knowledge of the anatomy and systematics of worms is necessary for the scientific diagnosis of helminthiasis. On the other hand, the physician has to carry out prophylaxis in the fight against worm diseases: for this, he is obliged to know the biology of parasitic worms, be familiar with their development cycle, and be able to orient himself in the question of intermediate hosts, etc.; in other words, the physician must receive a serious biological-helminthological education. But the task of medical Helminthology is not exhausted by this. The physician-helminthologist must comprehensively study not only the parasites but also the diseases caused by them from the point of view of their etiology, pathogenesis, diagnostics, clinical picture, pathological anatomy, prophylaxis, therapy, general sanitation, etc.; finally, in the hands of the physician-helminthologist, there is always material concerning the intimate aspects of the relationships between the parasite and the host, material on questions of the biology and pathology of parasitism, which has the deepest scientific and practical interest. The host exerts an undoubted multifaceted influence on the parasite, placing the latter in the specific conditions of a certain physical-chemical environment, etc.; as a result, this environment leaves an indelible imprint on the entire organization of the parasite, often distorting the latter to the extreme. The study of the ecology of parasitic worms is therefore of great interest from the point of view of general biology. On the other hand, the parasite exerts a serious influence on the host by the production of, if nothing else, toxins, which, in turn, causes a reaction of the host's organism in the sense of the formation of antibodies, etc. To grasp all these relationships, to study their essence, and to try to find practical application for these reactions is one of the most rewarding tasks of medical Helminthology. Thus, the content of medical Helminthology consists of the following chapters: 1. Study of parasitic worms of humans from the point of view of a) anatomy, b) physiology, c) embryology, d) biochemistry, e) biology, f) systematics, g) ecology, h) geography. 2. Study of the human organism from the point of view of the influence of parasitic worms on it. 3. Study of the therapy, prophylaxis, and epidemiology of all kinds of worm diseases of humans. The scope of medical Helminthology depends not only on the abundance of worm species capable of parasitizing in different organs and tissues of humans but also on their zoological diversity, depending on their belonging to three different types of the animal kingdom. Helminthological institutions. Helminthology at the present time is cultivated, mainly, on the basis of parasitological and tropical institutes. Such are the helminthological departments in Rio de Janeiro (at the Oswaldo Cruz Institute), in London, Hamburg, Liverpool, and Berlin. There are a number of large helminthological institutes connected with higher schools: medical, veterinary, and biological departments of universities. Helminthology has reached a special flourishing in the U.S.A. and Japan. In the USSR, medical helminthological institutions are connected, mainly, with tropical institutes (Moscow, Kharkov, Erivan, Bukhara), while veterinary helminthological institutions are connected with scientific research institutions (State Institute of Experimental Veterinary Medicine in Moscow, Kharkov). Helminthological literature is almost entirely represented in parasitological journals. The most important periodical publications are: 'Journal of Helminthology' (London), 'Parasitology' (Cambridge), 'Journal of Parasitology' (Urbana), 'Annales de Parasitologie' (Paris), 'Zeitschrift für Parasitenkunde' (Berlin), 'Archiv für Schiffs- und Tropenhygiene' (Hamburg), 'Annals of Tropical Medicine and Parasitology' (Liverpool); Helminthology is richly represented in Japanese journals; works on medical Helminthology (except for Russian ones) are almost exhaustively reviewed by 'Zentralblatt für die gesamte Hygiene' (Berlin) and 'Tropical Diseases Bulletin' (London). In the USSR, questions of helminthology are most often covered in the 'Russian Journal of Tropical Medicine' (Moscow), 'Bulletin of Microbiology, Epidemiology and Parasitology' (Saratov), and 'Transactions of the State Institute of Experimental Veterinary Medicine' (Moscow). Helminthological museums most often do not exist as independent institutions but are located at various laboratories and institutes.

The largest repositories of helminthological collections are concentrated in Washington, Vienna, and Berlin. In Moscow, the Central Helminthological Museum is located at the Helminthological Department of the State Institute of Experimental Veterinary Medicine, which is one of the largest in the world (about 35,000 vials of parasitic worms). The value of this museum lies in the fact that it was assembled through the dissection of animals and humans using Skryabin's method of complete helminthological autopsies (see Helminthological research methods). Helminthological expeditions are most often carried out not as independent organizations, but are conducted incidentally and jointly with some general zoological or other expedition. Since 1919, specifically helminthological expeditions have been regularly conducted in the USSR, and by the summer of 1928, 62 had already been registered. The expeditions work using the method of complete helminthological autopsies and, year after year, reveal the helminth fauna of humans and animals in different regions of the USSR. The Commission for the Study of the Helminth Fauna of the USSR (organized in 1922 in Moscow) is attached to the Zoological Museum of the All-Union Academy of Sciences, serving as an association that unites all helminthologists of the USSR: physicians, veterinarians, and naturalists; its tasks are to coordinate helminthological work, organize helminthological expeditions, and conduct work on training new cadres of helminthologist specialists.