A VIRUS containing ribonucleic acid (RNA) which is able to change its genetic material into deoxyribonucleic acid (DNA) using an ENZYME called reverse transcriptase. This conversion enables the retrovirus to become integrated into the host cell's DNA. Retroviruses are believed to be involved in the development of some cancers; they are also associated with disorders linked with an impaired immune system (see IMMUNITY). HIV is a retrovirus.

Retroviruses are also used in the development of gene therapy (see GENETIC ENGINEERING).