HTLV-1, or Human T-cell Lymphotropic Virus type 1, is a retrovirus that primarily infects T-cells, a type of white blood cell crucial for the immune system. It is transmitted through bodily fluids, including blood, breast milk, and sexual contact. While many people infected with HTLV-1 remain asymptomatic, the virus can lead to serious health issues, such as Adult T-cell Leukemia/Lymphoma (ATLL) and HTLV-1-associated Myelopathy (HAM). HTLV-1 is most prevalent in certain regions, including parts of Japan, the Caribbean, and sub-Saharan Africa. Diagnosis typically involves blood tests to detect the virus or antibodies. Preventive measures focus on safe practices, such as using sterile needles and practicing safe sex, to reduce transmission risks.