Human T-cell lymphotropic virus-1 (HTLV-1) is part of a group of viruses, including HTLV-I, -II, and -III (also known as HIV-1 and HIV-2). It is endemic in many countries, principally Japan, the Caribbean, and central Africa, and it is estimated that 10-20 million people worldwide are infected. Most people do not develop any symptoms; however, about 1 in 20 people will develop adult T-cell leukemia/lymphoma or HTLV-1 associated myelopathy (a chronic nervous system disease). HTLV-1 infection is usually diagnosed by serology assays detection of HTLV-1 specific IgG or IgM antibodies.