Human T-lymphotropic virus type I infection

Human T-cell lymphotropic virus type-I (HTLV-I) is aetiologically associate d with adult T-cell leukaemia/lymphoma (ATL). HTLV-I infection can also lea d to various non-malignant diseases, for example, HTLV-I associated myelopa thy/tropical spastic paraparesis and HTLV-I uveitis. HTLV-I is endemic in s outhern Japan and the Caribbean. HTLV-I infection is mainly transmitted by either breast-feeding, sexual intercourse or blood transfusions. Primary pr evention of HTLV-I in endemic areas by screening of blood and by refraining from breastfeeding have been successful. The incidence of ATL is rather lo w among HTLV-I carriers (< 5%). The precise mechanism of development of ATL remains unknown. It is a multiple-step process which does not require vira l expression in the later stages of leukaemogenesis. Many samples have muta tions of the tumour suppressor genes, p53 and/or p16(INK4A). Four subtypes of ATL have been identified, each having distinctive clinical features. Mon oclonal integration of HTLV-I proviral DNA into tumour cells is found in ea ch of the subtypes. At present, no effective therapy for ATL exists.