ERVW-1 and tropical spastic paraparesis: Humoral immune responses against Gag and Env are significantly increased in blood of HAM/TSP vs. other HTLV-1 infected individuals; whereas anti-Tax and anti-HBZ Ab levels are similar in HTLV-1 infected subjects (Enose-Akahata et al., 2012a; Shiohama et al., 2016).