HTLV

HTLV, or human T-lymphotropic virus, refers to a group of human retroviruses in the genus deltaretrovirus. The best known members are HTLV-1 and HTLV-2, with additional, less well characterized members HTLV-3 and HTLV-4 that have been described in a small number of human infections. HTLV-1 is the most clinically significant member and is associated with certain malignant and neurological diseases, while HTLV-2 is less clearly linked to disease. HTLV-3 and HTLV-4 have uncertain pathogenicity and are the subject of ongoing study.

HTLV is transmitted primarily through contact with infected bodily fluids. Major routes include sexual transmission, blood exposure (such as transfusion or sharing contaminated needles), and from mother to child via breastfeeding. Infected individuals may remain asymptomatic for many years; disease, when it occurs, often develops decades after acquisition.

Geographically, HTLV-1 is endemic in parts of southwestern Japan, the Caribbean, sub-Saharan Africa, and some areas of South America. HTLV-2 is found among certain Indigenous populations in the Americas and in people who inject drugs. HTLV-3 and HTLV-4 are rare and have been identified in limited populations. The overall global burden is not uniform, and many infections are not associated with overt disease.

Clinical disease associated with HTLV-1 includes adult T-cell leukemia/lymphoma (ATLL) and HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP). HTLV-2 may be linked to milder neurological syndromes in some cases; for HTLV-3 and HTLV-4, disease associations remain unclear. HTLV infections are diagnosed by serologic testing with confirmatory and molecular methods; there is no widely available vaccine, and treatment focuses on managing symptoms and HTLV-1–related conditions, as antiviral therapy has limited efficacy. Prevention emphasizes exposure avoidance, blood product screening, safe sex, and counseling for breastfeeding decisions in some cases.