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 diseases, including Adult T-cell Leukemia/Lymphoma (ATLL) and HTLV-I-associated myelopathy (HAM), which can lead to severe health complications. The virus is most prevalent in certain regions, such as Japan, Caribbean countries, and parts of Africa. Many individuals infected with HTLV-I remain asymptomatic for years, but some may develop serious health issues later in life. Early detection and monitoring are essential for managing the potential effects of the virus.