Science and Development Network
News, views and information about science, technology and the developing world
.jpg){kind=small}
.jpg){kind=spacer}
.jpg){kind=small}
Definitions
Below is a directory of terms used to talk about malaria. Most definitions have been taken from the US Centers for Disease Control and Prevention (CDC).
A
Anaemia
A reduction in the number of circulating red blood cells or in the quantity of haemoglobin.
Anopheles
A genus of mosquito, some species of which can transmit human malaria.
Antibiotic
Antimicrobial agent made from a mould or a bacterium that kills or slows the growth of other microbes, specifically bacteria. Example: penicillin.
Antibody
A protein produced by 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 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, antiviral agents, antifungal agents, and antiparasitic drugs.
Antimicrobial resistance
Antimicrobial resistance is the result of microbes changing in their DNA to reduce or eliminate the effectiveness of drugs, chemicals, or other agents to cure or prevent infections.
Artemisinin
The WHO's recommended drug for malaria, derived from the Chinese sweet wormwood plant, Artemisia annua.
Autochthonous
Malaria transmitted by mosquitoes. Autochthonous malaria can be indigenous (in a geographic area where malaria occurs regularly) or introduced (in a geographic area where malaria does not occur regularly).
B
Bacteria
(singular: Bacterium) Single-celled organisms that are found throughout nature and can be beneficial or cause disease.
C
Cerebral malaria
A complication of Plasmodium falciparum malaria, in which infected red blood cells obstruct blood circulation in the small blood vessels in the brain. When cerebral malaria is present, the disease is classified as severe malaria.
Chemoprophylaxis
Taking antimalarial drugs to prevent the disease.
Chloroquine
A drug used against malaria. A very safe and inexpensive drug, its value has been compromised by the emergence of chloroquine-resistant malaria parasites.
Clinical cure
Elimination of malaria symptoms, sometimes without eliminating all parasites. See "radical cure" and "suppressive cure/treatment."
Congenital malaria
Malaria in a newborn or infant, transmitted from the mother at birth.
Cryptic
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).
D
DEET
N,N-diethylmetatoluamide, an ingredient of insect repellents.
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.
E
Efficacy
The power or capacity to produce a desired effect.
ELISA
Enzyme-linked immunosorbent assay. ELISA 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
The process of removing something permanently.
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.
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.
F
Falciparum
See Plasmodium.
G
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, begin to sexually reproduce, which starts the extrinsic (sporogonic) cycle of the parasite in the mosquito. Gametocytes of Plasmodium falciparum are typically crescent or sickle-shaped (from the latin: falcis=sickle).
Gene
The segment of DNA on a chromosome that contains the information necessary to make a protein. Genes are the unit by which biological traits are inherited. [JIC]
Genetic diversity
The variety of different types of genes in a species or population.
H
Haematological
Having to do with the blood.
Haemoglobin
The red, oxygen-carrying protein found in red blood cells.
Haemolysis
Destruction of red blood cells. Malaria causes haemolysis when the parasites rupture the red blood cells in which they have grown.
Hepatocytes
Liver cells.
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.
Hypoglycaemia
Low blood glucose. Hypoglycaemia can occur in malaria. In addition, treatment with quinine and quinidine stimulate insulin secretion, reducing blood glucose.
I
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.
Immunisation
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.
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.
Imported malaria
Malaria acquired outside a specific geographical area.
Incubation period
The interval of time between infection by a micro-organism 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 seven to 40 days, depending on species.
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, or shared needles or syringes).
Infection
The invasion of an organism by a pathogen such as bacteria, viruses, or parasites. Some, but not all, infections lead to disease.
Introduced malaria
Mosquito-borne transmission of malaria from an imported case in a geographic area where malaria does not occur regularly.
L
Larvae
Mosquito larvae are immature, wingless forms that develop in water.
Leukocyte
White blood cell.
Leukocytosis
Increase in total white blood cell count.
Leukopenia
Decrease in total white blood cell count.
M
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.
Molecular methods
Methods that are based on identification and characterisation 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 that ingest bacteria, dead cells, and other debris.
O
Oocyst
A stage in the lifecycle of malaria parasites, oocysts are rounded cysts 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.
P
Parasite
Any organism that lives in or on another organism without benefiting the host organism.
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 two per cent").
Pathogen
Bacteria, viruses, parasites or fungi can cause disease.
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, four species of which infect humans: Plasmodium falciparum, P vivax, P ovale and P malariae.
Platelets
Small, irregularly-shaped bodies in the blood that contain granules. These cells are important components of the blood 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.
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, parasitise other organisms for their nutrients and life cycle.
Pyrethroid
A class of insecticides derived from the natural pyrethrins; used to treat bednets.
Q
Quinine
A drug used against malaria, obtained from the bark of the cinchona tree.
R
Radical cure
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 (short term relapse or delayed), due to the survival of malaria parasites in red blood cells.
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
Treatment of houses 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.
Resistance
The ability of an organism to develop strains that are 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.
S
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.
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.
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.
T
Thrombocytopenia
Low platelet count, that can lead to impaired blood clotting and spontaneous bleeding. Thrombocytopenia can occur in severe Plasmodium falciparum malaria.
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.
V
Vaccine
A preparation that stimulates an immune response that can prevent an infection or create resistance to an infection.
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
Z
Zoophilic
Zoophilic mosquitoes are mosquitoes that prefer to take blood meals on animals.
