Regarding the maintenance of neurons, it is assumed that variations in NGF levels could be related to one of the main diseases caused by HTLV-1, i.e., HAM, which is a slow-progressing inflammatory neurological disease characterized by axonal degeneration and demyelination, mainly in the corticospinal tract (group of axons that extend from the brain to the spinal cord) [32]. Here, NGF is linked to tropical spastic paraparesis.