Human T-lymphotropic virus type I (HTLV-I) is a retrovirus that primarily infects T-lymphocytes, a type of white blood cell crucial for the immune system. It is transmitted through bodily fluids, including blood, breast milk, and sexual contact. HTLV-I is associated with several health conditions, including adult T-cell leukemia and HTLV-I-associated myelopathy. Infection with HTLV-I is relatively common in certain regions, particularly in Japan, Caribbean countries, and parts of Africa. Many individuals remain asymptomatic for years, but some may develop serious health issues later in life. There is currently no cure for HTLV-I, making prevention and early detection important.