Metagonimosis

Metagonimosis, a helminthic disease of the human intestine and fish-eating mammals, the causative agent of which is the trematode Metagonimus yokogawai Katsurada 1912, belonging to the family Heterophyidae. Synonyms of the parasite: M. romanicus Ciurea 1915, M. parvus Ciurea 1915, Loossia romanica Ciurea 1915, Loossia parva Ciurea 1915, Loossia dobrodjiensis Ciurea. The body is pear-shaped, 1.0 to 2.5 mm long, with a maximum width in the posterior half of the body of 0.4–0.8 mm. The cuticle is covered with small spines, more powerfully expressed in the anterior half of the body. The oral sucker reaches 0.07–0.09 mm in diameter, the pharynx is 0.05–0.06 x 0.045–0.055 mm; there is a prepharynx; the postpharynx is elongated; the intestinal trunks extending from it are directed toward the lateral edges of the parasite and run parallel to the latter to the posterior end of the body. The genital sucker is shifted from the midline of the body to the right side of the parasite, adjoining the inner edge of the right intestine, approximately at the level of the middle of the body length. This sucker is oval in shape, its long axis directed at an acute angle to the axis of the parasite's body. The length of this formation is 0.12–0.145 mm with a width of 0.075–0.10 mm. The rounded-oval testes reach 0.20–0.30 mm in diameter, are arranged obliquely to each other and occupy the posterior section of the body, adjoining with their edges to the terminal sections of the intestine. Between the testes is a V-shaped excretory bladder. In front of the anterior testis, most often medially, is the receptaculum seminis, to the anterior or lateral edge of which adjoins a spherical ovary, localizing along the midline of the body. The vitellaria are located in the posterior half of the body, adjoining the lateral edges, consist of a relatively small number of large follicles (about 10–12 on each side) and cover the intestinal trunks. The terminal male apparatus consists of a powerful vesicula seminalis, having the appearance of a 2–3-jointed tube, the fragments of which are located at an acute angle in relation to each other. The uterus is localized in the posterior half of the body, filling with its convolutions all the spaces between the sexual elements. The terminal section of the uterus, directed toward the genital sucker, passes anterior to the terminal part of the vesiculae seminalis. Mature eggs of a light grayish-yellowish shade reach 0.026–0.032 mm in length with a width of 0.015–0.017 mm. The pole of the egg where the operculum is located is somewhat narrower than the opposite, more rounded end, on which a small button-like thickening of the shell is noticeable. Biology is characterized by the presence of 2 intermediate hosts: the first is the mollusk Melania libertina, the second is salmonid fish (Plecoglossus altivelis) and some cyprinid fish (crucian carp, ide, etc.). The parasite is widely distributed in Japan, Korea, and China. In the USSR, the parasite was confirmed in the Far East in the lower reaches of the Amur and along the tributaries of the Ussuri among the small peoples of the North—Gilyaks, Golds, Ulchs, and Udege, who consume completely raw fish. According to the survey data of 1929 (by the 60th Union Helminthological Expedition), 13.6% of the native population of the Far Eastern Territory is infested with this parasite, which localizes in the small intestine. Clinically, M. manifests itself only with intense infestation and is characterized by phenomena of dyspepsia, diarrhea, and anemia. Therapy: administration of a laxative salt; after 8 hours—thymol in a dose of 2.0 three times in a row every 2 hours; 3 hours after the last dose—a laxative salt. On the second day, a new administration of thymol of 2.0 three times with two-hour intervals. After 2 hours—a laxative salt. Thus, for the entire course of treatment, 12.0 of thymol is used (Skryabin, Podyapolskaya, and Shikhobalova). Prophylaxis comes down to consuming well-cooked fish and protecting water bodies from contamination with feces. It would be advisable to carry out mass deworming of metagonimosis-infected dogs and cats, however, this measure is practically not feasible yet.

METAZOA, a name denoting the entire aggregate of multicellular animals in contrast to single-celled ones, Protozoa. M. are characterized by the specialization of the cells that make up their body. Submitting to the principle of physiological division of labor, the body cells of M. differentiate in various directions, resulting in several types of cells that differ from each other in both structure and function: nervous, epithelial, muscular, reproductive, etc. To the number of M. belong 7 types of animals: coelenterates, sponges, worms, mollusks, arthropods, echinoderms, and chordates. Some zoologists distinguish sponges from typical M. in view of the absence in them of a clearly differentiated internal germ layer connected with the digestive function and the similarity of sponges with some colonial protozoa.