Parasitology

Parasitology is the science studying the complex and diverse set of phenomena of parasitism and, as such, based on its primary objects of study, belongs to the category of biological disciplines. Corresponding to the nature of the subject of study, one distinguishes the parasitology of humans, animals, and plants. The task of parasitology includes the study of the systematics of parasites and the identification of their fauna for one locality or another; the grouping of relevant facts is conducted either by hosts as a whole or by their individual organs. Furthermore, the study of the structure of parasites and their physiology allows one to note and explain the peculiar forms and functions of parasitic organisms, which are connected with the peculiarities of their habitat. For endoparasites, such an environment is the host organism, and various changes in it can very significantly influence the parasites living within it. Due to such relationships, the study of the therapy of invasive diseases belongs to the ecology of parasites, since with the introduction of medicinal substances into the host organism, the parasite's habitat changes. The next important task is the study of the biology of parasites, often connected with the completion of complex life cycles, and the influence of parasites on their hosts. The latter direction closely links parasitology with general pathology, pathological anatomy, serology, and the pathology and therapy of parasitic diseases. This same direction connects general or theoretical parasitology with applied parasitology of a medical or veterinary nature. Accounting for the harmfulness of parasites provides material for judging the economic significance of parasites and for identifying species of primary practical importance. In connection with the pathogenic significance of parasites, the necessity of studying the parasitological diagnosis of parasitic diseases becomes apparent, which is based on special methods of parasitological research. The therapy of parasitic diseases also has many peculiarities depending on the nature of the pathogen in each individual case. A natural conclusion of applied parasitological work is the search for measures to combat parasites and methods for preventing infection by them (or rather, the prophylaxis of parasitic diseases). For their purposes, the named branches of parasitology utilize the most diverse methods of research, which makes parasitology as a whole a complex of various sections of theoretical and applied sciences (biology, medicine, veterinary medicine, animal husbandry, agronomy, economics, etc.) that is enormous in size and importance. The official subdivision of parasitology into branches or departments is performed either according to the principle of the parasites' belonging to specific hosts or according to the systematic position of the parasites. In the first case, one distinguishes medical parasitology (i.e., of humans), veterinary parasitology, and the parasitology of commercial and wild animals. According to the second principle, parasitology is divided into protozoology (see), or the study of parasitic protozoa, helminthology (see), or the study of worms, and arachnology and entomology (see)—the study of parasitic arachnids and insects. In the French understanding, parasitology also encompasses plant parasites. The history of parasitology is composed of the course of development of its aforementioned systematic subdivisions and certain key stages in the evolution of related disciplines. Parasites have been known to humans since deep antiquity. The Egyptians knew of lice, fleas, ascarids, pinworms, and tapeworms. Until the 17th century, there was no progress in parasitology, as for the entire preceding time (about 16 centuries!), the meager data of Hippocrates and Galen regarding a few parasitic worms dominated. The second half of the 17th century was marked by the use of the microscope for the study of small objects; Leeuwenhoek discovered parasitic protozoa—coccidian oocysts in the liver of a rabbit and flagellates in human feces (Giardia intestinalis). Redi is the father of parasitology. His manual on parasites provided a mass of new information, in particular regarding worms discovered in the most diverse organs of hosts. Redi proved the absence of spontaneous generation of insects. In 1687, the itch mite was discovered. Also notable are the works of Swammerdam and other microscopists on the anatomy and biology of parasitic insects. The study of parasitic worms in the 18th century degraded due to the refusal to recognize the pathogenicity of parasitic worms. However, the 19th century was the beginning of the true flourishing of parasitology, the method of which increasingly strengthened the experiment (Kuchenmeister, Leuckart, and others). Complex life cycles of worms and parasitic protozoa are unraveled; intermediate hosts for various parasitic worms are established, and such hosts turned out to be not only vertebrates but also arthropods in the form of crustaceans and insects. In the field of protozoology, the 19th century was marked by the discovery of parasitic amoebae of humans, the malaria plasmodium (Laveran), trypanosomes, and many others. Especially important was the establishment of the facts of the transmission of certain parasitic protozoa and pathogenic bacteria by means of vectors (see). The development of parasitology is closely connected with the development of tropical medicine, the need for the study of which was dictated by the imperialist colonial policy of European states. Depending on the belonging of parasites to three types of animals, three branches of parasitology became isolated in their specialization: protozoology, helminthology, and entomology; however, the presence of intermediate hosts and the simultaneous parasitism of various parasites in the organism of hosts smooth out the sharpness of the boundaries between the branches of parasitology; this concerns especially those sections of it which can be characterized as general parasitology, which deals with the study of the regularities of parasitism and the entire complex of questions of the relationships between parasite and host. The 20th century is marked by the further brilliant development of parasitology and the recognition of the extraordinary practical significance of this science. The further development of parasitology is ensured by its great theoretical and enormous practical significance. There exist special parasitological institutes (e.g., The Molteno Institute for Research in Parasitology at Cambridge University); zoological departments of some universities have chosen various branches of parasitology as their specialty (Königsberg under M. Braun); parasitology has received special development in institutes of applied significance, where it is differentiated by departments and laboratories according to its systematic subdivisions. This is the case in tropical institutes (London, Hamburg, etc.), some Pasteur institutes (Paris, Algiers, Tunis), and special laboratories of an industrial nature (for plant pests, ichthyological institutes, fur-bearing animal nurseries, etc.). In the USSR, parasitological work is conducted in the Department of Parasitology and in the Malaria Commission of the Zoological Museum of the Academy of Sciences of the USSR, in certain departments of the State Institute of Experimental Medicine and the State Institute of Experimental Veterinary Medicine (protozoology and helminthology), in tropical institutes, some sanitary-bacteriological and veterinary-bacteriological institutes, in the sector for livestock pests of the All-Union Institute of Plant Protection of the Lenin Academy of Agricultural Sciences, in the laboratory of the Department of General Biology and Parasitology of the Military Medical Academy, and others. In the USSR, the Russian Parasitological Society in Leningrad also functions. Besides various laboratory studies, complex parasitological expeditions are finding increasingly wide application as a method (e.g., the Central Asian Parasitological Expedition of 1928 of the Academy of Sciences of the USSR, the Murgab Parasitological Expedition of the Academy of Sciences of the USSR and the People's Commissariat of Health of Turkmenistan in 1930, the Kara-Kala Parasitological Expedition of 1931 of the Academy of Sciences of the USSR, etc., expeditions of the Moscow and Bukhara Tropical Institutes, etc.). The teaching of parasitology is provided for along medical lines by the separation of an independent course in parasitology at the Military Medical Academy under the Department of General Biology, at the Kazan, Central Asian, and some other medical institutes; in veterinary institutes, departments of parasitology and invasive diseases have been organized; some biological faculties of universities also devote attention to the teaching of parasitology (Leningrad). Finally, in Leningrad, the Department for Livestock Pests functions, which is effectively a higher educational institution training specialists in the control of ectoparasites of domestic animals and humans (in particular, in the application of the aerial method in combination with ground-based mosquito control—in the system of anti-malarial measures), organized by the Association for Pest Control (OBV). In the Leningrad Institute for Pest Control (LINBOV), a correspondence course of study was opened there as well. In the OBV system, the first technical school for pest control workers with regard to ectoparasites is being organized (in Kustanai). Furthermore, from time to time, regular or sporadic courses on various branches of parasitology are conducted (Tropical Institute in Moscow, local courses at various republican and regional institutes). Finally, it is necessary to mention specialized parasitological laboratories, e.g., the laboratory for fish diseases of the Leningrad Ichthyological Institute, which encompasses the study of the entire complex of fish parasites.