Primer: Human T-cell leukemia virus type 1 (HTLV-1).

The human T-cell leukemia virus HTLV-1-also known as human T-lymphotropic virus type 1-was the first human retrovirus discovered. Unlike HIV-1, it has been present in humans for tens of thousands of years, and in consequence HTLV-1 is exquisitely adapted to persist in the individual host. Its life history therefore differs fundamentally from that of HIV-1 in key respects. HTLV-1 causes an aggressive hematological malignancy known as adult T-cell leukemia-lymphoma (ATL) and a progressive inflammatory disease of the central nervous system, HTLV-1-associated myelopathy (HAM), in a proportion of infected people. These conditions impose a significant health burden in countries where the virus is endemic.