Transmission electron micrograph (TEM) image revealed the presence of both the human T-cell leukemia type-1 virus (HTLV-1), (also known as the human T lymphotropic virus type-1 virus), and the human immunodeficiency virus (HIV). Human T-cell leukemia virus type-1 (HTLV-1), a human oncoretrovirus, is the etiologic agent of adult T-cell leukemia, and of tropical spastic paraparesis/HTLV-1-associated myelopathy. Two closely related retroviruses, HIV-1 and HIV-2, have been identified as causing AIDS in different geographic regions. HIV-1 causes most cases of AIDS in the U.S., with only a few cases of HIV-2 having been found in the U.S. Epidemiologically, HIV-2 has been found to be mostly an infection of persons from West Africa.