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Human T-cell lymphotropic virus type 1 (HTLV-1) is a retrovirus that can be transmitted through blood transfusion. In the absence of donor screening, HTLV-1 can be efficiently transmitted via infected lymphocytes. Lifeblood uses a strategy of identifying at-risk donors and limited screening for HTLV antibodies to minimize the risk of transmission. The estimated median transfusion-transmission residual risk for HTLV in Australia is less than 1 per million units.

HTLV-1 belongs to the Retroviridae family and is closely related to human T-cell lymphotropic virus type 2 (HTLV-2). The virus has at least seven subtypes and is considered to have originated from primate T-cell lymphotropic virus (PTLV) in African non-human primates.

HTLV-1 infection is associated with several clinical symptoms, including adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). The risk of developing disease is related to the age and immune competence of the host, the mode of infection, and the age at which infection is acquired. Approximately 3-6% of individuals infected with HTLV-1 develop clinical disease over the course of their life.

HTLV-1 infection can also cause other diseases, including infective dermatitis, skin abnormalities, ocular lesions, inflammatory polyarthropathy, and polymyositis. High rates of HTLV-1 infection and HTLV-1-associated diseases contribute substantially to the burden of ill-health and early mortality among Indigenous Australians living in central Australia and the Top End of the Northern Territory.