Human T cell leukemia virus type 1 (HTLV-1) is a type C retrovirus primarily endemic to Japan, Central and South America, the Middle East, regions of Africa, and the Caribbean (1-7). Currently, an estimated 10− 20 million people worldwide are infected with this virus (8-10). Although the majority of infected individuals remain asymptomatic, HTLV-1 is the causative agent of a number of disorders, notably adult T cell leukemia (ATL) and a progressive demyelinating neurologic disorder, HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP)(11). HTLV-1 presents as either ATL or HAM/TSP in approximately 2− 3% of seropositive individuals after a long asymptomatic period of latency (12). The likelihood of a small percentage of HTLV-1-infected patients developing HAM/TSP has been postulated to be dependent on several factors including human histocompatibility leukocyte antigen (HLA) subtype (13), viral strain (14-16), mode of infection (17), and proviral DNA load (18-22). In addition to ATL and HAM/TSP, HTLV-1