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Cross-resistance: resistance selected by one drug which, in turn, confers resistance to one or more drugs not included in the current treatment
DNA: deoxyribonucleic acid, the genetic material of a cell
Drug resistance: decreased susceptibility to a drug
Drug resistance mutation: a change in amino acid associated with increased resistance of HIV to an anti-retroviral drug
Gene: a segment of DNA coding for a particular protein or protein sub-unit
Genotype: specific sequence of nucleotides that determines the genes of HIV-1
Genotypic resistance: presence of mutations to nucleotides that increase resistance of HIV to one or more anti-retroviral drugs
Genotypic tests: conducted to determine the presence of mutations in the nucleotide sequence of the viral genome
HIV: Human immunodeficiency virus
Incidence: the number of new occurrences of a disease in a given population during a specified period of time
Multi-drug resistance: increased resistance of HIV to more than one class of drugs
Mutation: genetic change in the viral nucleotide sequence
Nucleotide: a monomeric unit consisting of a sugar, phosphate, and nitrogenous base
PCR: polymerase chain reaction, a molecular technique used to amplify nucleotide sequences
Phenotype: characteristics and growth properties of HIV-1
Phenotypic resistance: when four or more times the amount of drug is required to inhibit viral growth by 50% (inhibitory concentration 50)
Phenotypic tests: used to determine the susceptibility of a virus to drug in a virus culture assay
Prevalence: the number people with the disease in a given population who are alive during a specified period of time
Primary mutation: mutation in the viral nucleotide sequence that, in and of itself, is strongly associated with conferring increased resistance of HIV to an anti-retroviral drug
Primary resistance: increased resistance of HIV to anti-retroviral drugs seen in individuals who have never before received treatment and so, presumably, have been infected with drug-resistant virus
Protease: an enzyme that breaks down proteins to their subunits or component peptides
Recombinant: HIV-1 containing a sequence corresponding to a mixture of more than one subtype in the envelope gene
Reverse transcriptase: an enzyme that is unique to all retroviruses. It reads the genetic information of the retrovirus, which is RNA, and makes a DNA copy.
RNA: ribonucleic acid, a polymer of nucleotides involved in protein synthesis
RT-PCR: PCR using the enzyme reverse transcriptase (RT), a molecular technique used to amplify RNA sequence into DNA
Secondary mutation: mutation in the viral nucleotide sequence, which, in combination with other mutations, confers increased resistance of HIV to a drug
Secondary resistance: increased resistance of HIV to drugs seen in individuals already receiving treatment (presumably a result of treatment failure)
Subtype: also referred to as clade, a group of related HIV variants classified according to degree of genetic similarity
Wild type virus: the most commonly occurring form of HIV-1
1. Some definitions are adapted from the HIV and AIDS in Canada surveillance report to December 31, 2000 and from the International Consultation on Monitoring the Emergence of Antiretroviral Resistance sponsored by WHO, UNAIDS and ISS (October, 2000).