What is Resistance?

Mutations & Resistance in HIV
- How Resistance Evolves

Managing Resistance to HIV Therapy

Resistance Quiz

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Mutations & Resistance in HIV

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HIV Mutations
HIV infection is characterised by high rates of viral replication, eventually leading to depletion of CD4 cells and disease progression^1,2. A high frequency of replication results in a high frequency of viral mutations, resulting in many different strains of virus, each with slightly different genes. The mutation rate in HIV is also very high because the enzyme responsible for copying the viral genetic code is inefficient and makes numerous mistakes. It has been calculated that every possible single point HIV mutation may occur more than 10,000 times a day in an infected person³.

Some mutations kill the virus, and some cause insignificant changes. But other mutations have an advantageous effect on viral behaviour, resulting in increased virulence, faster replication, increased cytotoxicity or reduced sensitivity to antiviral drugs^4,5.

Resistance to Antiretroviral Drugs
Resistance can develop to all drugs, including all classes of anti-HIV drugs, for example reverse transcriptase inhibitors, and drugs taken to treat opportunistic infections.

Drugs used in HIV therapy work by inhibiting specific viral enzymes essential to the virus' normal function or replication. To become resistant to an antiviral drug, the virus must acquire a mutation that changes the enzyme in a way that makes it insensitive to drug action but does not damage the virus.

Because HIV mutations happen frequently by chance, an untreated individual infected with HIV will have a number of different strains of the virus, some of which may be naturally resistant to different antiretroviral drugs^6-8. Before treatment is started, however, the mutant (resistant) strains are uncommon, and the natural (wild-type) strain predominates because it replicates more efficiently³.