varices – extended or swollen veins in the liver that can burst. They can be a complication of cirrhosis.

viral load – the amount of virus in a sample of blood or other fluid. With HIV this is commonly the amount of HIV in a millilitre (mL) of blood. See viral load test.

viral load test – a test that detects whether a virus is present (qualatitive) or that measures the amount of virus (quantitative).

This is usually in a sample of blood, but a viral load test can also be used to check viral levels in other samples including genital fluid, semen or spinal fluid.

Results are given as the number of copies of virus in a millilitre of blood (copies/mL).

viral rebound – when your viral load has been undetectable (under 50 copies/mL) and then becomes detectable. Sometimes viral rebound can be a lab error, sometimes a small temporary blip, and sometimes a real rebound that shows your virus may have developed resistance to one or more of the drugs in a combination treatment. See: virological failure.

viral tropism see tropism.

virion – the name for a virus when it is not inside a cell, for example when new viral material leaves a CD4 cell and is floating in blood or plasma

virological failure – the term for when viral load levels never reach undetectable, or if they rebound to higher levels after previously being undetectable. See clinical failure.

virology – the study of viruses.

virus – an infectious organism that can only reproduce inside the cell of another plant or animal.