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Anemia: A reduction in the number of circulating red blood cells or in the quantity of hemoglobin.

Anopheles: A genus of mosquito, some species of which can transmit human malaria.

Anorexia: Lack of appetite, lack of desire or interest in food.

Anthropophilic: Describes mosquitoes that prefer to take blood meals from humans.

Antibiotic: A drug that kills or slows the growth of bacteria. Example: penicillin.

Antibody: A specialized serum protein (immunoglobulin or gamma globulin) produced by B lymphocytes in the blood in response to an exposure to foreign proteins (“antigens”). The antibodies specifically bind to the antigens that induced the immune response. Antibodies help defend the body against infectious agents such as bacteria, viruses or parasites.

Antigen: Any substance that stimulates the immune system to produce antibodies. Antigens are often foreign substances such as parts of invading bacteria, viruses or parasites.

Antimicrobial agents: The drugs, chemicals, or other substances that kill or slow the growth of microbes. They include antibacterial drugs (which kill bacteria), antiviral agents (which kill viruses), antifungal agents (which kill fungi), and antiparasitic drugs (which kill parasites).

Antimicrobial resistance: Antimicrobial resistance is the result of microbes changing in ways that reduce or eliminate the effectiveness of drugs, chemicals, or other agents to cure or prevent infections.

Aralen: A brand name for chloroquine phosphate.

Artemisinins: A class of drugs used for the treatment (not prevention) of malaria usually as a part of a combination therapy, derived from the sweet wormwood or Qinghao plant (Artemisia annua).

Atovaquone: A drug used against malaria. It is found in the combination atovaquone-proguanil which can be used for both prevention and treatment.

Autochthonous: Regarding malaria, it refers to local transmission by mosquitoes. This can either be indigenous (a geographic area where malaria occurs regularly) or introduced (in a geographic area where malaria does not occur regularly).

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Bacteria: (singular: Bacterium) Single-celled organisms that are found throughout nature and can be beneficial or cause disease.

B-cell (B-lymphocyte): White blood cells of the immune system that are derived from the bone marrow and spleen. B cells develop into plasma cells, which produce antibodies.

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Carbamate: A chemical product used as an insecticide.

Cerebral malaria: A severemalaria syndrome in which infected red blood cells obstruct blood circulation in the small blood vessels in the brain and/or release cytokines that disrupt normal brain function.

Chemoprophylaxis: The use of antimalarial drugs to prevent malaria disease.

Chloroquine: A drug used against malaria for both prevention and treatment. A very safe and inexpensive drug, its value has been compromised by the emergence of chloroquine-resistant malaria parasites.

Cinchonism: Side effects from quinine or quinidine. Includes tinnitus, headache, nausea, diarrhea, altered auditory acuity, and blurred vision. The term derives from cinchona bark, the natural source of quinine.

Clindamycin: An antibiotic that can be used for the treatment of malaria in combination with a second drug, usually quinine or quinidine.

Clinical cure: Elimination of malaria symptoms, sometimes without eliminating all parasites. See “radical cure” and “suppressive cure/treatment.”

Coma: A decreased state of consciousness from which a person cannot be roused.

Congenital malaria: Malaria in a newborn or infant, transmitted from the mother.

Cryptic malaria: A case of malaria where epidemiologic investigations fail to identify an apparent mode of acquisition (this term applies mainly to cases found in non-endemic countries).

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DEET: N,N-diethylmetatoluamide, an ingredient of insect repellents.

Defervescence: The reduction of a patient’s abnormally elevated temperature into the normal range.

Deltamethrin: An insecticide.

Diurnal: During the daytime.

Doxycycline: An antibiotic drug that can be used against malaria; by itself for prevention or in combination with either quinine or quinidine when used for treatment.

Drug resistance: Drug resistance is the result of microbes changing in ways that reduce or eliminate the effectiveness of drugs, chemicals, or other agents to cure or prevent infections.

Dyspnea: Shallow, labored breathing.

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Efficacy: The power or capacity to produce a desired effect.

Elimination: In the context of malaria, reducing all local transmission down to zero cases within a defined geographic location.

ELISA: Enzyme-linked immunosorbent assay. This laboratory test is now often used to determine whether mosquito salivary glands are positive for sporozoites.

Endemic: Where disease occurs on a consistent basis.

Endophagic: An endophagic mosquito is a mosquito that feeds indoors.

Endophilic: An endophilic mosquito is a mosquito that tends to inhabit/rest indoors. Endophilism facilitates the blocking of malaria transmission through application of residual insecticides to walls.

Epidemic: The occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time.

Epidemiology: The study of the distribution and determinants of health-related states or events in specified populations, and the application of this study to the control of health problems.

Eradication: In the context of malaria, reducing the number of malaria parasites that circulate in the natural world to zero.

Erythrocyte: A red blood cell.

Erythrocytic stage: A stage in the life cycle of the malaria parasite found in the red blood cells. Erythrocytic stage parasites cause the symptoms of malaria.

Etiology: The cause or origin of a disease or disorder; the study of the factors that cause disease and of the method of their introduction into the host.

Exoerythrocytic stage: A stage in the life cycle of the malaria parasite found in liver cells (hepatocytes). Exoerythrocytic stage parasites do not cause symptoms.

Exophagic: An exophagic mosquito is a mosquito that feeds outdoors.

Exophilic: An exophilic mosquito tends to inhabit/rest outdoors. Residual insecticides in buildings are less effective at controlling exophilic mosquitoes.

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Falciparum: See Plasmodium.

Fansidar: Brand name of sulfadoxine-pyrimethamine, a drug used against malaria. Its value has been compromised by the emergence of drug-resistant malaria parasites.

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G6PD deficiency: An inherited abnormality that causes the loss of a red blood cell enzyme. People who are G6PD deficient should not take the antimalarial drug primaquine.

Gametocyte: The sexual stage of malaria parasites. Male gametocytes (microgametocytes) and female gametocytes (macrogametocytes) are inside red blood cells in the circulation. If they are ingested by a female Anopheles mosquito, they undergo sexual reproduction which starts the extrinsic (sporogonic) cycle of the parasite in the mosquito. Gametocytes of Plasmodium falciparum are typically banana or crescent-shaped (from the latin falcis=sickle).

Gene: The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule.

Genetic diversity: The variety of different types of genes in a species or population.

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Halofantrine: A drug used against malaria in some countries, but not recommended by CDC.

Hematocrit: The amount of blood consisting of red blood cells, measured as a percentage.

Hematologic: Having to do with the blood.

Hemoglobin: The red, oxygen-carrying protein found in red blood cells.

Hemolysis: Destruction of red blood cells. Malaria causes hemolysis when the parasites rupture the red blood cells in which they have grown.

Hepatocytes: Liver cells.

Hepatomegaly: Enlarged liver.

Hypnozoite: Dormant form of malaria parasites found in liver cells. Hypnozoites occur only with Plasmodium vivax and P. ovale. After sporozoites (inoculated by the mosquito) invade liver cells, some sporozoites develop into dormant forms (the hypnozoites), which do not cause any symptoms. Hypnozoites can become activated months or years after the initial infection, producing a relapse.

Hypoglycemia: Low blood glucose. Hypoglycemia can occur in malaria. In addition, treatment with quinine and quinidine stimulate insulin secretion, reducing blood glucose.

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Icterus: See jaundice.

Immune system: The cells, tissues and organs that assist the body to resist infection and disease by producing antibodies and/or cells that inhibit the multiplication of the infectious agent.

Immunity: Protection generated by the body’s immune system, in response to previous malaria attacks, resulting in ability to control or lessen a malaria attack.

Immunization: The process or procedure by which a subject (person, animal, or plant) is rendered immune, or resistant to a specific disease. This term is often used interchangeably with vaccination or inoculation, although the act of inoculation does not always result in immunity.

Imported malaria: Malaria acquired outside a specific geographic area.

Incubation period: The interval of time between infection by a microorganism and the onset of the illness or the first symptoms of the illness. In malaria, the incubation is between the mosquito bite and the first symptoms. Incubation periods range from 7 to 40 days, depending on species.

Indoor residual spraying (IRS): Treatment of houses where people spend night-time hours, by spraying insecticides that have residual efficacy (i.e., that continue to affect mosquitoes for several months). Residual insecticide spraying aims to kills mosquitoes when they come to rest on the walls, usually after a blood meal. Â

Infection: The invasion of an organism by a pathogen such as bacteria, viruses, or parasites. Some, but not all, infections lead to disease.

Indigenous malaria: Mosquito-borne transmission of malaria in a geographic area where malaria occurs regularly.

Induced malaria: Malaria acquired through artificial means (e.g. blood transfusion, shared needles or syringes, or malariotherapy).

Introduced malaria: Mosquito-borne transmission of malaria from an imported case in a geographic area where malaria does not occur regularly.

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Jaundice: Yellow discoloration of skin and eyes due to elevated blood levels of bilirubin.

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Knowlesi: See Plasmodium

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Lariam: Brand name of mefloquine, a drug used against malaria for both prevention and treatment.

Larvae: An immature stage of a developing mosquito. Mosquito larvae are wingless and develop in water.

Leukocyte: White blood cell.

Leukocytosis: Increase in total white blood cell count.

Leukopenia: Decrease in total white blood cell count.

Lymphocyte: Leukocyte with a large round nucleus and usually a small cytoplasm. Specialized types of lymphocytes have enlarged cytoplasms and produce antibodies. Other specialized lymphocytes are important in cellular immune responses.

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Macrogametocyte: The female form of the gametocyte.

Malarone: Brand name of atovaquone-proguanil, a drug used against malaria for both prevention and treatment.

Malariae: See Plasmodium.

Merozoite: A daughter cell formed by asexual development in the life cycle of malaria parasites. Liver-stage and blood-stage malaria parasites develop into schizonts which contain many merozoites. When the schizonts are mature, they (and their host cells!) rupture; the merozoites are released and infect red blood cells.

Mefloquine: A drug used against malaria for both prevention and treatment.

Microgametocyte: The male form of the gametocyte.

Molecular methods: Laboratory techniques that are based on identification and characterization of certain molecules and gene sequences of a pathogen’s genetic makeup.

Monocyte: Leukocyte with a large, usually kidney-shaped nucleus. Within tissues, monocytes develop into macrophages which ingest bacteria, dead cells, and other debris.

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Oocyst: A stage in the life cyle of malaria parasites, oocysts are rounded structures located in the outer wall of the stomach of mosquitoes. Sporozoites develop inside the oocysts. When mature, the oocysts rupture and release the sporozoites, which then migrate into the mosquito’s salivary glands, ready for injection into the human host.

Ovale: See Plasmodium.

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Parasite: Any organism that lives in or on another organism without benefiting the host organism; commonly refers to pathogens, most commonly in reference to protozoans and helminths.

Parasitemia: The presence of parasites in the blood. The term can also be used to express the quantity of parasites in the blood (e.g., “a parasitemia of 2%”).

Paroxysm: A sudden attack or increase in intensity of a symptom, usually occurring in intervals.

Pathogen: Bacteria, viruses, parasites or fungi can cause disease.

Permethrin: A pyrethroid insecticide.

Phagocyte: A type of white blood cell that can engulf and destroy foreign organisms, cells and particles. Phagocytes are an important part of the immune system.

Plasmodium: The genus of the parasite that causes malaria. The genus includes many species. The four species that naturally infect humans are  Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale and Plasmodium malariae. Plasmodium knowlesi is a zoonotic species that naturally infects macaques in Southeast Asia that can also infect humans. Â

Platelets: Small, irregularly-shaped bodies in the blood that contain granules. These cells are important components of the blood coagulation (clotting) system.

Polymorphic: Literally meaning having more than one form. In terms of genes it means that there are several variants (alleles) of a particular gene that occur simultaneously in a population.

Presumptive treatment: Treatment of clinically suspected cases without, or prior to, results from confirmatory laboratory tests.

Primaquine: A drug used against malaria for the prevention of P. vivax or for the eradication of the hypnozoites of P. vivax and P. ovale.

Proguanil: A drug used against malaria. It is found in the combination atovaquone-proguanil which can be used for both prevention and treatment.

Prophylaxis: See “chemoprophylaxis.”

Protozoan: Single-celled organism that can perform all necessary functions of metabolism and reproduction. Some protozoa are free-living, while others, including malaria parasites, parasitize other organisms for their nutrients and life cycle.

Pyrethroid: A class of insecticides derived from the natural pyrethrins.

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Quinine: A drug used against malaria, obtained from the bark of the cinchona tree. Quinine is used for treatment but not prevention of malaria.

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Radical cure: (also: radical treatment) Complete elimination of malaria parasites from the body; the term applies specifically to elimination of dormant liver stage parasites (hypnozoites) found in Plasmodium vivax and P. ovale.

Recrudescence: A repeated attack of malaria due to the survival of malaria parasites in red blood cells.

Radical treatment: See radical cure.

Relapse: Recurrence of disease after it has been apparently cured. In malaria, true relapses are caused by reactivation of dormant liver stage parasites (hypnozoites) found in Plasmodium vivax and P. ovale.

Residual insecticide spraying: See indoor residual spraying.

Resistance: The ability of an organism to develop ways to be impervious to specific threats to their existence. The malaria parasite has developed strains that are resistant to drugs such as chloroquine. The Anopheles mosquito has developed strains that are resistant to DDT and other insecticides.

Rigor: Severe shaking chill.

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Schizogony: Asexual reproductive stage of malaria parasites. In red blood cells, schizogony entails development of a single trophozoite into numerous merozoites. A similar process happens in infected liver cells.

Schizont: A developmental form of the malaria parasite that contains many merozoites. Schizonts are seen in the liver-stage and blood-stage parasites.

Sequelae: Morbid conditions following as a consequence of a disease.

Serology: The branch of science dealing with the measurement and characterization of antibodies and other immunological substances in body fluids, particularly serum.

Species: Organisms in the same genus that have similar characteristics.

Splenectomy: Removal of the spleen.

Splenomegaly: Enlargement of the spleen. Found in some malaria patients. Splenomegaly can be used to measure malaria endemicity during surveys (e.g., in communities or in schoolchildren).

Sporozoite: A stage in the life cycle of the malaria parasite. Sporozoites are produced in the mosquito and migrate to the mosquito’s salivary glands. They can be inoculated into a human host when the mosquito takes a blood meal on the human. In the human, the sporozoites enter liver cells where they develop into the next stage of the malaria parasite life cycle (the liver stage or exo-erythrocytic stage).

Sporozoite rate: The proportion of female anopheline mosquitoes of a particular species that have sporozoites in their salivary glands (as seen by dissection), or that are positive in immunologic tests to detect sporozoite antigens.

Strain: A genetic variant within a species.

Sulfadoxine-pyrimethamine: A drug used against malaria. Its value has been compromised by the emergence of drug-resistant malaria parasites

Suppressive treatment: Treatment intended to prevent clinical symptoms and parasitemia through destruction of parasites in red blood cells. It does not prevent infection because the parasite stages inoculated by the mosquito (sporozoites) will survive and invade the liver with the development of liver-stage parasites. It is when the parasites leave the liver cells to invade the blood that they are eliminated. Because the blood- stage parasites are the ones that cause disease, eliminating these stages will prevent symptoms.

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Tachycardia: Increased heart rate.

Tachypnea: Increased rate of breathing.

Tafenoquine: A drug used against malaria for the prevention of malaria or the eradication of the hypnozoites of P. vivax and P. ovale.

Tetracycline: An antibiotic drug that can be used against malaria for treatment only, not prevention.

Thrombocytopenia: Low platelet count that can lead to impaired blood clotting and spontaneous bleeding.

Tinnitus: Ringing sound in the ears, a common side effect of quinine treatment.

Trophozoite: A developmental form during the blood stage of malaria parasites. After merozoites have invaded the red blood cell, they develop into trophozoites (sometimes, early trophozoites are called “rings” or “ring stage parasites”); trophozoites develop into schizonts.

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Vaccine: A preparation that stimulates an immune response that can prevent an infection or create resistance to an infection.

Vector: An organism (e.g., Anopheles mosquitoes) that transmits an infectious agent (e.g. malaria parasites) from one host to the other (e.g., humans).

Vector competence: The ability of a vector (e.g., Anopheles mosquitoes) to transmit a disease (e.g., malaria).

Virus: A microorganism composed of a piece of genetic material – RNA or DNA – surrounded by a protein coat. To replicate, a virus must infect a cell and direct its cellular machinery to produce new viruses.

Vivax: See Plasmodium

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Zoonosis: A disease that naturally occurs in animals that can also occur in humans.

Zoophilic: Zoophilic mosquitoes are mosquitoes that prefer to take blood meals on animals.

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Page last reviewed: November 15, 2018