SPOROZOA

From Big Medical Encyclopedia

SPOROZOA (Sporozoa) — class of parasitic elementary (one-celled) animals. M. V. Krylov, A. A. Dobrovolsky (1980), etc. carry S. to type of a subkingdom of protozoa.

For the first time S. were found in 1879 it. scientist Leyka mouth (R. Leuckart). In total class C. combines apprx. 2000 separate types protozoa (see), a part from to-rykh are causative agents of invasive diseases of the person and animals (see. Coccidiosis , Malaria , Sarcosporidiosis , Toxoplasmosis ).

Alternation of asexual reproduction (at nek-ry S. this way of reproduction can be absent), sexual process and a sporogony, and also existence of a zygotic reduction (the first nuclear fission of a zygote — reducing) and education a sporocyst and (or) oocysts (zygocysts) is characteristic of a life cycle of the majority of types of S.

Main stages of a life cycle of S.: the schizogony (multiple fission) leading to increase in number of individuals of a parasite, a gamogoniya (formation of gametes), fertilization and a sporogony (formation from a zygote of sporozopt). In the period of a sporogony conditions for an invazirovaniye of other individuals who are owners of this species of a parasite are created.

Fig. 1. The scheme of a life cycle of Sporozoa (on the example of koktsidiya of the sort Eimeria): I \first cycle of a schizogony (multiple fission of sporozoit); II and III — recycles of a schizogony (multiple fission of merozoites; IV \a gametogonium (differentiation of merozoites in macro - and microgametocytes, originative macro - and to microgametes); V \sporogony; 1 — the created one-nuclear sporozoite; 2 — a young schizont (the sporozoite which was implemented into a cell of the owner); 3 — the growing multinuclear schizont; 4 — the schizont which is breaking up to merozoites; 5 — merozoites; 6 — formation of macrogametes; 7 — formation of microgametes; 8 — a microgamete; 9 — a zygocyst (it is formed as a result of copulation macro - and microgametes); 10 — the zygocyst which started a sporogony; 11 — a zygocyst with four sporoblasts which are formed as a result of meiotic division of a zygote; 12 — further development of sporoblasts; 13. — a mature zygocyst with four disputes (in everyone a dispute there are about two sporozoites which at hit in an organism of the owner are capable by the beginning of a new life cycle).

Development of the cells of the owner S. which got inside proceeds at representatives of different types of S. differently. At sporozoit of representatives of Coccidiomorpha which got in cells of an organism owner the schizogony (fig. 1) begins. At the same time there is an initial repeated nuclear fission to the subsequent vypochkovyvaniye of daughter cells (merozoites) in the quantity corresponding to number of products of nuclear divisions. Merozoites make several recycles of a schizogony then a part of merozoites is differentiated in macro - and a part — in microgametocytes, originative macro - and to microgametes. Gametes whipgraft, the zygote is surrounded with a zygocyst (oocyst), inside the cut begins process of a sporogony. The sporogony begins meiotic division (see. Meiosis ), the formed haploid kernels share then mitotic (see. Mitosis ). Division of cytoplasm of a zygote leads to formation of one-nuclear sporozoit, to-rye can form the groups protected by additional cystic educations — disputes, or sporocysts. At hit of sporozoit in an organism of the owner a new life cycle of Page begins. Lack of asexual reproduction and formation of zygocysts without sporocyst is characteristic of most of representatives of Gregarinomorpha (see. Gregarines ).

Fig. 2. Diagrammatic representation of a structure of sporozoit and merozoites of Sporozoa: 1 — an apical polar ring; 2 — a mikronema; 3 — a roptriya; 4 — Golgi's complex; 5 — a kernel; 6 — a mitochondrion; 7 — a distal polar ring; 8 — a kernel; 9 — the site of a cytoplasmic reticulum; 10 — a micropore; 11 — a pellicle; 12 — a conoid.

Sporozoita and all S.' merozoites are constructed according to one plan (fig. 2). These are the extended cells covered with a three-membrane pellicle in a cut there are ultramicroscopic embolies — micropores, or the ultracytoostomies participating in food of Page. Under a pellicle there is a system of the microtubules connecting to apical and distal polar rings. In the forefront of a cell the so-called apical complex of organoids including a conoid, roptriya and mikronema is located. The conoid has the form of the cylinder or the truncated cone, is formed of fibrilla. Roptriya, the organellas which are available in different quantity — extended, extending in the tail surrounded with one membrane and coming to an end with an opening on the front end of a cell. Mikronema — the numerous minute electron-dense structures which are located near roptriya. All this complex performs, apparently, secretory function, and the secret allocated to them promotes penetration of sporozoit or merozoites in a cell of the owner. Existence of an apical complex is reflected in the second name C., widespread in the world literature — Apicomplexa.

One S. (the majority of koktsidiya) have one owner, and their distribution is carried out by means of oocysts through the environment. At other S., e.g. at plasmodiums — activators malaria (see) — two owners (in one there passes the cycle of asexual reproduction, in another — sexual process and a sporogony). The invasion is carried out or during a sting (e.g., at a mosquito by transfer of causative agents of malaria), or through the food, water and objects of use contaminated by the excrements containing oocysts (see. Coccidiosis ).

S.'s systematics according to M. V. Krylov and A. A. Dobrovolsky's classification (1980) looks as follows. The type of Sporozoa breaks up to 3 classes: Perkinsemorpha, Gregarinomorpha and Coccidiomorpha. The class Perkinsemorpha, representatives to-rogo parasitize at mollusks, is studied insufficiently, and many scientists dispute its belonging to S. V the class Coccidiomorpha 2 subclasses (Coccidiomorphina and Piroplasmomorphina), and the Coccidiida group is of interest to medicine, Isospora parasitizing at the person, Sarcocystis and Toxoplasma treat Krom. Are a part of a subclass of Piroplasmomorphina Haemosporidia group to which carry causative agents of malaria Plasmodium, and the Piroplasmida group including causative agents of diseases of farm and other animals.



Bibliography: Krylov M. V. and Dobrovolsky A. A. A macrosystem and genealogy of Sporozoa, in book: The principles of creation of a microsystem of one-celled animals, under the editorship of M. V. Krylov and Ya. I. Skorobogatov, page 62, D., 1980; Krylov M. V. and To about with t e N to about JI. A. Morfofunktsionalnaya the organization of Sporozoa, in book: Evolution and genealogy of one-celled animals, under the editorship of M. V. Krylov, page 42, L., 1981.


O. I. Chibisova.

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