= Human immunodeficiency virus
= HIV
{c}
{synonym}
<Human immunodeficiency virus> is the name used for two related <retroviruses>, <HIV-1> and <HIV-2>, whose infection can lead to <AIDS>. The <virus> and the disease stage are distinct: <AIDS> is the most advanced stage of <human immunodeficiency virus> infection, rather than the name of every infection.<Human Immunodeficiency Virus in the NIH HIV Glossary>[Human Immunodeficiency Virus (HIV), definition and two types]{ref}
Both belong to <Lentivirus>, within <Orthoretrovirinae> and <Retroviridae>. Their replication connects an <RNA> <genome>, a <DNA> intermediate formed by <reverse transcription>, and an integrated <provirus>. In primate lentiviruses, entry involves <CD4> and a chemokine receptor; identifying a <cell> receptor and measuring subsequent virus production are distinct experimental questions.<Lentivirus report by the International Committee on Taxonomy of Viruses>[Distinguishing features, primate lentivirus receptors]{ref}<Retroviridae report by the International Committee on Taxonomy of Viruses>[Table 1, replication]{ref}
A constructed measurement example distinguishes a molecular quantity from a biological outcome. Suppose an assay reports 100 viral <RNA> copies in an analysed equivalent of one microlitre of plasma. The corresponding <viral load> is $100\times1000=100{,}000$ RNA copies per millilitre, assuming the assay's stated calibration and volume correction. That count is not a direct count of infectious <virions>, and it does not by itself specify a person's disease stage. The measured material, normalization and biological question must all be stated.
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