This is a retrovirus that infects T lymphocytes and can lead to chronic infection; about 1% of patients with an HTLV-1 infection develop progressive myelopathy clinically manifesting with spastic paraplegia, low back pain, and bladder/bowel dysfunction. This has been termed HTLV-1 associated myelopathy and tropical spastic paraparesis (HAM/TSP). HTLV-1 is transmitted by sexual contact, breastfeeding, or blood transfusions. HTLV-1 itself is largely asymptomatic for years, even decades, and only later manifests as HAM/TSP. HTLV-1 infection is also associated with aggressive T cell leukemia (adult T cell leukemia, ATL) in about 5% of patients. HTLV-1 is endemic in Japan, South America, the Caribbean, and west, central and southern Africa. HIV, which was not included here, can also manifest with progressive myelopathy and can parallel the AIDS dementia complex spectrum. Herpesvirus including HSV-1/2, VZV, EBV, CMV, HHV-6, and HHV-7 can cause infectious myelitis. These generally manifest with acute and subacute myelitis (manifesting over days to weeks). CMV myelitis is almost exclusively seen in immunosuppressed patients. CMV myelitis can have normal MRI imaging in up to half of cases. Mycoplasma pneumoniae can manifest with parainfectious myelopathy, which presents rather acutely and would not be associated with a prolonged progressive disease course.