Human T-lymphotropic virus: HTLV. A retrovirus that causes adult T-cell leukemia. HTLV is endemic (constantly present) in southern Japan and the Caribbean basin and occurs sporadically in Africa, Latin America, the Middle East, and the US.
Adult T-cell leukemia occurs in less than 5% of people with HTLV infection, with an average latency period (a long delay) of more than 30 years. HTML can be transmitted by blood transfusions or tissue transplants. The virus is also known as human T-lymphotropic virus-I (HTLV-I).