HTLV-I, adult T-cell leukemia, and tropical spastic paraparesis.

Human lymphotropic retroviruses have been identified as the etiological agents of adult T-cell leukemia and acquired immunodeficiency syndrome (AIDS). Human T-lymphotropic virus type I (HTLV-I) has been linked to the etiology of ATL, and human immunodeficiency virus type I (HIV-1) has been identified as the cause of AIDS. Both retroviruses are T-cell tropic. HTLV-I is a transforming virus, whereas HIV-1 is a cytopathic virus and kills the cells it infects. HTLV-I has recently been identified from some patients with tropical spastic paraparesis, and it appears that HTLV-I infection alone or in the presence of other cofactors may be important in the development of this neurological dysfunction.