SUMMARY NOTES OF LECTURES IN ZOOLOGY

Module 1. ZOOLOGY AS A SCIENCE. SUBKINGDOM PROTOZOA

Content Module 1.2. Subkingdom Protozoa. General Characteristics

Topic 1.2.3. Phylum Apicomplexa

General characteristics of the phylum. Origin, evolution, paleontological data, modern diversity, geographic distribution, and Significance in nature and human life. Overview of major taxonomic groups important for human life and the functioning of natural ecosystems. Class Sporozoea. Subclass Gregarinia. Subclass Coccidia. Subclass Piroplasmia. Over 6,000 species. Intracellular, less commonly cavity parasites of animals. Structural Features of active life cycle phases—merozoites and sporozoites. Pellicle (Cell/33.html">Plasma Membrane, with a layer of microtubules on the inner side). Apical complex (apex): penetration Organelles—conoid (spirally twisted fibrils tightly adjacent to each other, a pair of preconoidal bodies), flask-shaped rhoptries, and thread-like micronemes. Micropore (cytostome)—cellular Mouth (ultracytostome)—pinocytosis. Several ultracytostomes. Metagenesis with zygotic reduction; in some species, the sexual process is unknown. Sporozoites (4, 8, or more) enclosed in a protective oocyst shell—enter Cells—feed and grow—trophozoite stage—schizogony—merozoites—exit The Cell and infect new cells—after several generations, gamonts are formed—gametogony—Gametes (isogamy and anisogamy)—zygote, surrounded by a wall (oocyst), Meiosis inside, and sometimes additional mitoses resulting in The formation of sporozoites, often covered with walls (spores).

Two classes: Sporozoea and Perkinsea, containing a single genus Perkinsus (parasites of marine Mollusks), with a poorly studied life cycle.

Class Sporozoea. Typical Structure. Subclasses Gregarinia, Coccidia, and Piroplasmia.

Subclass Gregarinia. Cavity parasites of invertebrates (intestine of Arthropods, mainly insects, less commonly in the body cavity and reproductive Organs; certain groups inhabit Annelids and Echinoderms). About 500 species. 0.016–16 mm. Species from the intestine of arthropods: epimerite, protomerite, deutomerite. Nucleus located in the deutomerite. The epimerite bears hooks or more complex appendages. Young specimen inside a cell, cytostome on the epimerite—intestinal lumen—sexual process, epimerite is discarded. Smooth movement: mucus is forcefully ejected through pores—jet propulsion. Most species lack schizogony: only gametogony and sporogony occur. Invasive stage—oocyst with sporozoites—host intestine—intestinal epithelial cells—intestinal lumen (organ cavities)—gamonts—pair up (syzygy)—common wall (gamontocyst)—mitotic divisions, multiple nuclei near the gamont surface—gametes and residual body—gametes of one gamont fuse in pairs with gametes of the other gamont (iso- or heterogamy)—zygotes become covered with a thick wall (oocysts inside the gamontocyst)—meiosis occurs first in each oocyst, followed by mitosis—several sporozoites (sporogony)—gamontocyst is swallowed by a new host. Polycystidae (Corycella armata from the intestine of whirligig beetle larvae, Clepsidrina blattarum from the cockroach intestine, etc.). Monocystidae parasitize the body cavity and Gonads and have a worm-like shape. Gregarines are studied for the biological control of pest insects.

Subclass Coccidia. Intracellular parasites of vertebrates, including humans. Heterogamy or oogamy: the macrogamont produces 1 macrogamete, while the microgamont produces several microgametes. Cause severe diseases. About 400 species.

Order Coccidiida. Parasites of birds and mammals, less frequently of other vertebrates, annelids, mollusks, and arthropods. Highly specialized parasites affecting young animals. Sporogony takes place in the external environment; one or two hosts. Asexual reproduction occurs in the intermediate host, whereas the sexual process occurs in the definitive host. Eimeria species are parasites of the intestinal tract or Liver cells; about ten species cause fatal diseases in sheep and goats, E. bovis in calves, E. stiedae in rabbits, E. tenella in chicks, and E. truncata in goslings. E. stiedae parasitizes the rabbit Organism: ingestion of oocysts with food—four spores, each containing two sporozoites—sporozoites enter the intestinal lumen, epithelium of the Small Intestine and liver—trophozoites (schizonts)—schizogony—merozoites enter the intestinal lumen and reinfect epithelial cells—the cycle repeats four to five times—micro- and macrogamonts—several microgametes or one macrogamete—copulation—zygote covered with a wall—oocyst excreted with feces into the environment—formation of sporozoites (sporogony). Without host alternation, schizogony and gametogony occur within the host, and sporogony takes place in the external environment. Parasite of many mammal species and humans—Toxoplasma gondii. About 80% of the world population is infected; Toxoplasmosis does not develop in all infected individuals. Life cycle involves two hosts. Definitive hosts are felines, while intermediate hosts include humans, rodents, ungulates, etc. It affects Brain cells and the reticuloendothelial system. Merozoites reproduce by endodyogeny—aggregates of merozoites become enclosed in a wall (cysts)—a cat consumes the meat—cyst wall dissolves—toxoplasms invade the intestinal epithelium and other organs—endodyogeny—merozoites return to the intestinal epithelial cells—sexual process (oogamy)—oocysts are excreted with feces—infection of intermediate and definitive (felines) hosts. Human infection occurs via: 1) careless handling of infected people or animals (merozoites are excreted with urine, mucus, or exudate); 2) infected cats (via oocysts); 3) poorly cooked or undercooked meat (pork, etc.). Clinical manifestations in humans: involvement of Lymph Nodes, Muscles, Nervous system, and visual organs. Pregnant women can transmit Toxoplasma to the fetus through the Placenta, resulting in Miscarriage or the birth of diseased children who frequently die.

Sarcosporidia—Muscle parasites of mammals; their life cycle is similar to that of toxoplasms. Definitive hosts are carnivorous mammals and humans, and intermediate hosts are various mammals and birds.

Order Haemosporidiida. Small sporozoites that parasitize THE RED Blood cells of vertebrates during a part of their life cycle. About 100 species. Human malaria is caused by 4 Plasmodium species: the CAUSATIVE AGENT OF tertian malaria is P. vivax; quartan malaria (erythrocytic schizogony lasts 72 h) is caused by P. malariae; malignant tropical malaria by P. falciparum; and tertian-type malaria (rarely occurring) by P. ovale.

P. vivax—bite of a malaria mosquito (Anopheles species)—sporozoites (lacking a conoid) enter the bloodstream—liver—schizonts break down (schizogony) into merozoites (hepatic schizogony)—one or more asexual generations—schizonts produce merozoites—entry into the bloodstream—invasion of erythrocytes—trophozoite (ring stage, schizont stage)—12–18 merozoites are formed (erythrocytic schizogony)—merozoites enter the bloodstream (48 h after merozoite invasion into the erythrocyte)—several cycles of erythrocytic schizogony—gamonts (gametogony)—further development in the mosquito intestine—macrogamonts (non-motile macrogamete), microgamont (eight motile flagellum-like microgametes)—copulation—amoeboid-motile zygote (ookinete)—epithelium of the mosquito intestinal wall—oocyst—mosquito body cavity (sporogony)—several thousand sporozoites—hemolymph, mosquito Salivary Glands—sporozoite development in the mosquito body takes one to four weeks. Two hosts—definitive (mosquito) and intermediate (human). Vector-borne disease without natural foci. No stage enters the external environment. Incubation period, fever spikes, paroxysms of chills and fever. The Emergence of merozoites triggers immune responses—small groups of merozoites in the blood are destroyed, whereas large numbers lead to subsequent synchronization. Malaria control: 1) Treatment of patients, 2) eradication of all Developmental Stages of malaria mosquitoes, 3) protection of people from their bites. Sporadic cases in individuals arriving from tropical regions. Prevalent in Tropical Asia, Africa, and Latin America. Malaria-like diseases occur in various mammals, birds (avian malaria), and reptiles. All of them are transmitted by mosquitoes.

Subclass Piroplasmia. Intracellular parasites of all vertebrate classes and hard ticks (Ixodida). About 200 species. Located inside erythrocytes and cells of The Lymphatic system, and in ticks—within the hemolymph and eggs. Not yet fully understood. Conoid is absent. Fever, presence of blood in the

urine. Without treatment, the animal dies. Babesia bigemina (Texas cattle fever) causes a mortality rate of 90–100%. Piroplasmoses of horses, dogs, and other domestic animals are extremely dangerous.