polymerase chain reaction

a laboratory method of amplifying low levels of specific microbial DNA or RNA sequences.


appearing in different forms.


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.


the genome of a virus integrated into the chromosome of the host cell. It is transmitted to all daughter cells.



a mixture of distinct but closely related viral genomes that exists in a virus-infected individual.



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.


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.


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.


ribonucleic acid.

RNA virus

a virus that contains RNA as its genetic material.


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.


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.


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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