Schizonts: Multinucleate cells or a stage in the development of sporozoan protozoa. It is exemplified by the life cycle of PLASMODIUM FALCIPARUM in the MALARIA infection cycle.Plasmodium falciparum: A species of protozoa that is the causal agent of falciparum malaria (MALARIA, FALCIPARUM). It is most prevalent in the tropics and subtropics.Trophozoites: Cells or feeding stage in the life cycle of sporozoan protozoa. In the malarial parasite, the trophozoite develops from the MEROZOITE and then splits into the SCHIZONT. Trophozoites that are left over from cell division can go on to form gametocytes.Theileria annulata: A protozoan parasite causing tropical theileriasis in cattle. It is transmitted by ticks of the Hyalomma genus.Erythrocytes: Red blood cells. Mature erythrocytes are non-nucleated, biconcave disks containing HEMOGLOBIN whose function is to transport OXYGEN.Theileria parva: A protozoan parasite that is the etiologic agent of East Coast fever (THEILERIASIS). Transmission is by ticks of the Physicephalus and Hyalomma genera.Malaria: A protozoan disease caused in humans by four species of the PLASMODIUM genus: PLASMODIUM FALCIPARUM; PLASMODIUM VIVAX; PLASMODIUM OVALE; and PLASMODIUM MALARIAE; and transmitted by the bite of an infected female mosquito of the genus ANOPHELES. Malaria is endemic in parts of Asia, Africa, Central and South America, Oceania, and certain Caribbean islands. It is characterized by extreme exhaustion associated with paroxysms of high FEVER; SWEATING; shaking CHILLS; and ANEMIA. Malaria in ANIMALS is caused by other species of plasmodia.Antigens, Protozoan: Any part or derivative of any protozoan that elicits immunity; malaria (Plasmodium) and trypanosome antigens are presently the most frequently encountered.Plasmodium: A genus of protozoa that comprise the malaria parasites of mammals. Four species infect humans (although occasional infections with primate malarias may occur). These are PLASMODIUM FALCIPARUM; PLASMODIUM MALARIAE; PLASMODIUM OVALE, and PLASMODIUM VIVAX. Species causing infection in vertebrates other than man include: PLASMODIUM BERGHEI; PLASMODIUM CHABAUDI; P. vinckei, and PLASMODIUM YOELII in rodents; P. brasilianum, PLASMODIUM CYNOMOLGI; and PLASMODIUM KNOWLESI in monkeys; and PLASMODIUM GALLINACEUM in chickens.Sarcocystis: A genus of protozoa found in reptiles, birds, and mammals, including humans. This heteroxenous parasite produces muscle cysts in intermediate hosts such as domestic herbivores (cattle, sheep, pigs) and rodents. Final hosts are predators such as dogs, cats, and man.Theileriasis: Infection of cattle, sheep, or goats with protozoa of the genus THEILERIA. This infection results in an acute or chronic febrile condition.Protozoan Proteins: Proteins found in any species of protozoan.Merozoites: Uninuclear cells or a stage in the life cycle of sporozoan protozoa. Merozoites, released from ruptured multinucleate SCHIZONTS, enter the blood stream and infect the ERYTHROCYTES.Sarcocystosis: Infection of the striated muscle of mammals by parasites of the genus SARCOCYSTIS. Disease symptoms such as vomiting, diarrhea, muscle weakness, and paralysis are produced by sarcocystin, a toxin produced by the organism.Haemosporida: An order of heteroxenous protozoa in which the macrogamete and microgamont develop independently. A conoid is usually absent.Malaria, Falciparum: Malaria caused by PLASMODIUM FALCIPARUM. This is the severest form of malaria and is associated with the highest levels of parasites in the blood. This disease is characterized by irregularly recurring febrile paroxysms that in extreme cases occur with acute cerebral, renal, or gastrointestinal manifestations.Coccidiostats: Agents useful in the treatment or prevention of COCCIDIOSIS in man or animals.Plasmodium vivax: A protozoan parasite that causes vivax malaria (MALARIA, VIVAX). This species is found almost everywhere malaria is endemic and is the only one that has a range extending into the temperate regions.Plasmodium berghei: A protozoan parasite of rodents transmitted by the mosquito Anopheles dureni.Antibodies, Protozoan: Immunoglobulins produced in a response to PROTOZOAN ANTIGENS.Antimalarials: Agents used in the treatment of malaria. They are usually classified on the basis of their action against plasmodia at different stages in their life cycle in the human. (From AMA, Drug Evaluations Annual, 1992, p1585)Life Cycle Stages: The continuous sequence of changes undergone by living organisms during the post-embryonic developmental process, such as metamorphosis in insects and amphibians. This includes the developmental stages of apicomplexans such as the malarial parasite, PLASMODIUM FALCIPARUM.Eimeria tenella: A species of coccidian protozoa that mainly infects domestic poultry.Aotus trivirgatus: A species in the family AOTIDAE, inhabiting the forested regions of Central and South America (from Panama to the Amazon). Vocalizations occur primarily at night when they are active, thus they are also known as Northern night monkeys.Chloroquine: The prototypical antimalarial agent with a mechanism that is not well understood. It has also been used to treat rheumatoid arthritis, systemic lupus erythematosus, and in the systemic therapy of amebic liver abscesses.Parasitic Sensitivity Tests: Tests that demonstrate the relative effectiveness of chemotherapeutic agents against specific parasites.Parasitemia: The presence of parasites (especially malarial parasites) in the blood. (Dorland, 27th ed)Apicomplexa: A phylum of unicellular parasitic EUKARYOTES characterized by the presence of complex apical organelles generally consisting of a conoid that aids in penetrating host cells, rhoptries that possibly secrete a proteolytic enzyme, and subpellicular microtubules that may be related to motility.Host-Parasite Interactions: The relationship between an invertebrate and another organism (the host), one of which lives at the expense of the other. Traditionally excluded from definition of parasites are pathogenic BACTERIA; FUNGI; VIRUSES; and PLANTS; though they may live parasitically.RNA, Protozoan: Ribonucleic acid in protozoa having regulatory and catalytic roles as well as involvement in protein synthesis.Genes, Protozoan: The functional hereditary units of protozoa.Coccidiosis: Protozoan infection found in animals and man. It is caused by several different genera of COCCIDIA.Inhibitory Concentration 50: The concentration of a compound needed to reduce population growth of organisms, including eukaryotic cells, by 50% in vitro. Though often expressed to denote in vitro antibacterial activity, it is also used as a benchmark for cytotoxicity to eukaryotic cells in culture.Plasmodium yoelii: A species of PLASMODIUM causing malaria in rodents.Malaria, Vivax: Malaria caused by PLASMODIUM VIVAX. This form of malaria is less severe than MALARIA, FALCIPARUM, but there is a higher probability for relapses to occur. Febrile paroxysms often occur every other day.DNA, Protozoan: Deoxyribonucleic acid that makes up the genetic material of protozoa.Saimiri: A genus of the family CEBIDAE consisting of four species: S. boliviensis, S. orstedii (red-backed squirrel monkey), S. sciureus (common squirrel monkey), and S. ustus. They inhabit tropical rain forests in Central and South America. S. sciureus is used extensively in research studies.Erythrocyte Membrane: The semi-permeable outer structure of a red blood cell. It is known as a red cell 'ghost' after HEMOLYSIS.Drug Resistance: Diminished or failed response of an organism, disease or tissue to the intended effectiveness of a chemical or drug. It should be differentiated from DRUG TOLERANCE which is the progressive diminution of the susceptibility of a human or animal to the effects of a drug, as a result of continued administration.Artemisinins: A group of SESQUITERPENES and their analogs that contain a peroxide group (PEROXIDES) within an oxepin ring (OXEPINS).Antigens, Surface: Antigens on surfaces of cells, including infectious or foreign cells or viruses. They are usually protein-containing groups on cell membranes or walls and may be isolated.Fluorescent Antibody Technique: Test for tissue antigen using either a direct method, by conjugation of antibody with fluorescent dye (FLUORESCENT ANTIBODY TECHNIQUE, DIRECT) or an indirect method, by formation of antigen-antibody complex which is then labeled with fluorescein-conjugated anti-immunoglobulin antibody (FLUORESCENT ANTIBODY TECHNIQUE, INDIRECT). The tissue is then examined by fluorescence microscopy.Malaria Vaccines: Vaccines made from antigens arising from any of the four strains of Plasmodium which cause malaria in humans, or from P. berghei which causes malaria in rodents.Microscopy, Fluorescence: Microscopy of specimens stained with fluorescent dye (usually fluorescein isothiocyanate) or of naturally fluorescent materials, which emit light when exposed to ultraviolet or blue light. Immunofluorescence microscopy utilizes antibodies that are labeled with fluorescent dye.Antigens: Substances that are recognized by the immune system and induce an immune reaction.