Glossary

A

acaricide

a pesticide that kills mites and ticks.

AIDS

acquired immunodeficiency syndrome, the end stage of HIV disease.

aminoglycoside

a class of antibiotic that acts by inhibiting microbial protein synthesis.

antibody

a protein produced by the immune system in response to the introduction of a substance (an antigen) recognized as foreign by the body's immune system. Antibody interacts with the other components of the immune system and can render the antigen harmless, although for various reasons this may not always occur.

antigen

a molecule capable of eliciting a specific antibody or T-cell response.

antigenic

having the properties of an antigen.

arbovirus

shortened form of arthropod-borne virus. Any of a group of viruses that are transmitted to man and animals by mosquitoes, ticks, and sand flies; they include such agents as yellow fever and eastern, western, and Venezuelan equine encephalitis viruses.

arenavirus

any of a group of viruses composed of pleomorphic virions of varying size, one large and one small segment of single-stranded RNA, and ribosomes within the virions that cause the virus to have a sandy appearance. Examples are Junin, Machupo, and Lassa fever viruses. Rodents are common reservoirs of the arenaviruses.

arthropod

as used in this report, refers to insects and ticks, many of which are medically important as vectors of infectious diseases.

arthropod-borne

capable of being transmitted by insect and tick (arthropod) vectors.



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Emerging Infections: Microbial Threats to Health in the United States Glossary A acaricide a pesticide that kills mites and ticks. AIDS acquired immunodeficiency syndrome, the end stage of HIV disease. aminoglycoside a class of antibiotic that acts by inhibiting microbial protein synthesis. antibody a protein produced by the immune system in response to the introduction of a substance (an antigen) recognized as foreign by the body's immune system. Antibody interacts with the other components of the immune system and can render the antigen harmless, although for various reasons this may not always occur. antigen a molecule capable of eliciting a specific antibody or T-cell response. antigenic having the properties of an antigen. arbovirus shortened form of arthropod-borne virus. Any of a group of viruses that are transmitted to man and animals by mosquitoes, ticks, and sand flies; they include such agents as yellow fever and eastern, western, and Venezuelan equine encephalitis viruses. arenavirus any of a group of viruses composed of pleomorphic virions of varying size, one large and one small segment of single-stranded RNA, and ribosomes within the virions that cause the virus to have a sandy appearance. Examples are Junin, Machupo, and Lassa fever viruses. Rodents are common reservoirs of the arenaviruses. arthropod as used in this report, refers to insects and ticks, many of which are medically important as vectors of infectious diseases. arthropod-borne capable of being transmitted by insect and tick (arthropod) vectors.

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Emerging Infections: Microbial Threats to Health in the United States B B lymphocyte one of two general categories of lymphocytes (white blood cells) involved in the humoral immune response. When help is provided by T lymphocytes, B lymphocytes produce antibodies against specific antigens. bacillus rod-shaped bacteria. bacteremia refers to the presence of bacteria in the blood. beta-lactam an active portion of an antibiotic (e.g., a penicillin or cephalosporin) that is part of the chemical structure of the antibiotic and that can be neutralized by a beta-lactamase produced by certain microorganisms (e.g., some staphylococci). beta-lactamase an enzyme that neutralizes the affect of an antibiotic containing beta-lactam. BL-4 level of containment required for safe handling of the most contagious pathogenic microbes. C calicivirus a family of small viruses; includes vesicular exanthem and seal plague viruses. carbapenem a class of antibiotic. cellular immunity, cell-mediated immunity a type of immune response in which subpopulations of T-cells (helper T-cells and killer T-cells) cooperate to destroy cells in the body that bear foreign antigens, such as bacteria. cephalosporin a class of antibiotic. clonal of or pertaining to a group of genetically identical organisms derived from a single parent or a DNA population derived from a single DNA molecule by replication in a bacterial or eucaryotic host cell. coagulase-negative refers to the inability of an organism, particularly staphylococci, to produce an enzyme that, in concert with a blood plasma cofactor, catalyzes the formation of fibrin from fibrinogen. coding sequence the order of nucleotide bases in a nucleic acid that specifies the production of a particular product, such as a protein. A change in the coding sequence (e.g., as a result of a mutation) can result in a change in the product. D DDT 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane or chlorophenothane, a pesticide. deletion mutation a mutation that results from the deletion of one or more amino acids present in the genetic material of the organism undergoing the mutation. disease as used in this report, refers to a situation in which infection has elicited signs and symptoms in the infected individual; the infection has become clinically apparent.

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Emerging Infections: Microbial Threats to Health in the United States DNA deoxyribonucleic acid, a carrier of genetic information (i.e., hereditary characteristics) found chiefly in the nucleus of cells. DNA virus a virus that contains only DNA as its genetic material. droplet nuclei the very small particles of moisture expelled when a person coughs, sneezes, or speaks that may transfer infectious organisms to another person who inhales the droplets. E ELISA enzyme-linked immunosorbent assay. An immunological technique used for the quantitation of antigen or antibody in a sample such as blood plasma or serum. In the assay, enzyme-labeled antigen or antibody is bound to a solid surface (such as beads, tubes, or microplate wells). After addition of the sample and a substrate, the presence of the desired antigen, antibody, or antigen-antibody complex is indicated by a color change based on a reaction of the enzyme with the substrate. endemic the condition in which a disease is present in a human community at all times. endogenous developing or originating from within the individual. enzootic refers to a disease (can be either low or high morbidity) that is endemic in an animal community. epidemic the condition in which a disease spreads rapidly through a community in which that disease is normally not present or is present at a low level. epizootic a disease of generally high morbidity that spreads rapidly through an animal population. escape mutant refers to the formation of a mutation in a population of microorganisms that allows the mutant organism to escape the immune response directed against it. etiologic agent the organism that causes a disease. etiology the cause or origin of a disease. F fluoroquinolone a class of antibiotic. G genetic adaptability the ability of a microorganism to adapt to its environment, often allowing it to avoid detection or an immune response generated against it. genome the complete genetic composition of an organism (e.g., human, bacterium, protozoan, helminth, or fungus), contained in a chromosome or set of chromosomes or in a DNA or RNA molecule (e.g., a virus). gram-negative refers to the inability of a microorganism to accept a certain stain. This inability is related to the cell wall composition of the microorganism and has been useful in classifying bacteria. gram-positive refers to the ability of a microorganism to retain a certain

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Emerging Infections: Microbial Threats to Health in the United States stain. This ability is related to the cell wall composition of the microorganism and has been useful in classifying bacteria. H hemagglutinin a molecule, such as an antibody or lectin, that agglutinates red blood cells. hemorrhagic fever a group of diverse, severe epidemic viral infections of worldwide distribution but occurring especially in tropical countries that are usually transmitted to humans by arthropod bites or contact with virus-infected rodents or monkeys and that share common clinicopathologic features (e.g., fever, hemorrhaging, shock, thrombocytopenia, neurological disturbances). Examples are Argentine, Bolivian, and Venezuelan hemorrhagic fevers; chikungunya; Rift Valley fever; and Ebola and Marburg virus diseases. HIV disease the broad spectrum of opportunistic infections and diseases that occur in an individual infected with the human immunodeficiency virus. humoral immunity antibody-mediated immunity; one of the mechanisms, using antibodies found in the blood and other body fluids, that the body uses to fight off infections. hyperendemic the condition in which a disease is present in a community at all times and with a high incidence. I iatrogenic any adverse condition, such as an infection, in an individual occurring as the result of treatment by a physician. immunocompromised a condition (caused, for example, by the administration of immunosuppressive drugs or irradiation, malnutrition, aging, or a condition such as cancer or HIV disease) in which an individual's immune system is unable to respond adequately to a foreign substance. immunosuppression the retardation or cessation of an immune response as a result of, for example, anticancer drugs. incidence as used in epidemiology, the number of new cases of a disease that occur in a defined population within a specified time period; the rate of occurrence. infection implies that an agent, such as a virus or bacterium, has taken up residence in a host and is multiplying within that host—perhaps with no outward signs of disease. Thus, it is possible to be infected with an agent but not have the disease commonly associated with that agent (although disease may develop at a later time). intramolecular recombination recombination that occurs within a single molecule, as opposed to between two molecules. L larvicide a material used to kill larval forms of pests and disease vectors. lentivirus a subfamily of the retroviruses.

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Emerging Infections: Microbial Threats to Health in the United States M mechanical vector a vector, not essential to the life cycle of the agent, that transmits an agent without itself becoming infected. microbial traffic the transfer of existing microbes to new host populations. monoclonal antibody immunoglobulins derived from a single clone of plasma cells. Moncolonal antibodies constitute a pure population because they are produced by a single clone in vitro and are chemically and structurally identical. mutation a transmissible change in the genetic material of an organism, usually in a single gene. N neuraminidase sialidase; an enzyme that catalyzes the hydrolysis of glucosidic linkages between a sialic acid residue and a hexose or hexosamine residue in glycoproteins, glycolipids, and proteoglycans. Neuraminidase is a major antigen of myxoviruses. nonsense mutation a mutation in which one of the three terminator codons (used to signal the end of a polypeptide) in messenger RNA appears in the middle of a genetic message, causing premature termination of transcription, resulting in the production of generally nonfunctional polypeptides. nosocomial infection hospital-acquired infection; an infection not present or incubating prior to admittance to the hospital. O opportunistic infection an infection caused by an organism that ordinarily does not cause disease but under circumstances such as impaired immunity, becomes pathogenic. organoleptic capable of receiving a sense impression. Organoleptic inspections are based on sensory perceptions (e.g., fish smells fresh or spoiled). P pandemic an epidemic that occurs worldwide. pathogen a microorganism that causes disease. pathogenic capable of causing disease. PCR see polymerase chain reaction. plasmid an extrachromosomal, self-replicating structure found in bacterial cells that carries genes for a variety of functions not essential for cell growth. Plasmids consist of cyclic double-stranded DNA molecules that replicate independently of the chromosomes and can be transmitted from one cell to another by conjugation or transduction. Episomes are genetic elements that can replicate in either of two alternative states—independently in the cytoplasm or as an integrated portion of the bacterial chromosome. point mutation a mutation resulting from a change in a single base pair in the DNA molecule, resulting from the substitution of one nucleotide for another.

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Emerging Infections: Microbial Threats to Health in the United States polymerase chain reaction a laboratory method of amplifying low levels of specific microbial DNA or RNA sequences. polymorphic appearing in different forms. prevalence as used in epidemiology, the total number of cases of a disease in existence at a specific time and within a well-defined area; the percentage of a population affected by a particular disease at a given time. provirus the genome of a virus integrated into the chromosome of the host cell. It is transmitted to all daughter cells. Q quasispecies a mixture of distinct but closely related viral genomes that exists in a virus-infected individual. R recombination the formation of new combinations of genes as a result of crossing over (sharing of genes) between structurally similar chromosomes, resulting in progeny with different gene combinations than in the parents. reservoir any person, animal, arthropod, plant, soil, or substance (or combination of these) in which an infectious agent normally lives and multiplies, on which it depends primarily for survival, and in which it reproduces itself in such manner that it can be transmitted to a susceptible vector. retrovirus any of a large family of RNA virtuses that includes lentiviruses and oncoviruses, so called because they carry reverse transcriptase. reverse transcriptase RNA-directed DNA polymerase; an enzyme, such as is found in the human immunodeficiency virus, that catalyzes the reaction that uses RNA as a template for double-stranded DNA synthesis. RNA ribonucleic acid. RNA virus a virus that contains RNA as its genetic material. S selective pressure pressure exerted on an organism by its environment that causes a change in the organism's ability to cope with that environment. septicemia, septicemic systemic disease associated with the presence and persistence of microorganisms in the blood. seroconversion the change of a serologic test result from negative to positive as a result of antibodies induced by the introduction of microorganisms into the host. serological the use of immune serum in any of a number of tests (agglutination, precipitation, enzyme-linked immunosorbent assay, etc.) used to measure the response (antibody titer) to infectious disease; the use of serological reactions to detect antigen.

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Emerging Infections: Microbial Threats to Health in the United States seronegative negative result in a serological test; that is, the inability to detect the antibodies or antigens being tested for. seropositive positive result in a serological test. serotype the characterization of a microorganism based on the kinds and combinations of constituent antigens present in that organism; a taxonomic subdivision of bacteria based on the above. slow virus any virus causing a disease characterized by a very long preclinical course and a very gradual progression of symptoms. strain a subgrouping of organisms within a species, characterized by some particular quality. syndrome a set of symptoms that may occur concurrently. T tubercle bacillus the bacterium that causes tuberculosis, Mycobacterium tuberculosis. V variolation a procedure, not used today, in which material from the pustule of an individual infected with smallpox (variola virus) was scratched into the skin of an infected person to induce immunity to the disease. vector a carrier, especially an arthropod, that transfers an infective agent from one host (which can include itself) to another. vector-borne transmitted from one host to another by a vector. virulence the degree of pathogenicity of an organism as evidenced by the severity of resulting disease and the organism's ability to invade the host tissues. Z zoonosis a disease of animals transmissible to humans. zoonotic pool the population of animals infected with nonhuman microbes that present a potential threat of transmission to humans.