Last updated: 15-Jan-2007
Human T Cell Lymphotropic Virus
An estimated 10 to 20 million people worldwide are infected with human T cell leukemia virus type I (HTLV-I).[1] Most of these carriers are asymptomatic (though capable of transmitting the infection), but 5 to 10% develop either adult T cell leukemia or a particular myelopathy, a neurologic disease characterized by demyelinating lesions in the brain and spinal chord.[2] Interestingly, these two conditions are very different, and rarely occur together in the same individual.[3] The fact that most infected people do not develop disease naturally raises questions about the factors and processes which prompt movement towards one or other of the symptomatic states.
For our purposes, it is useful to know that the 1 to 5% of infected individuals who develop leukemia demonstrate mucosal exposure to the virus as the route of transmission (as opposed to progression to myelopathy, a disease which favours infection via blood).[4] After transmission by whatever route, “the differential immune response mounted by the host…likely plays a key role in determining the outcome of HTLV-I infection.”[5]
Unfortunately, HTLV-induced malignancies do not respond to conventional chemotherapy; disease progression is often rapid, potentially leading to death within 2 years.[6]
The specific mechanisms by which leukemogenesis is initiated following HTLV-I infection remains a matter of intense investigation. The hope is that gaining understanding about disease pathways will lead to proven prevention or therapeutic measures, neither of which currently exists.[7] This makes early primary prevention all the more important. That is to say, modifying activity to eliminate viral exposure is the recommended course for individuals to follow. The main behavioural risk factors for contracting HTLV are intravenous drug use and multiple sexual contacts. Family members of HTLV-positive people also show a higher rate of infection.[8]
[1] Edlich RF, Arnette JA, Williams FM. Global epidemic of human T-cell lymphotropic virus type-I (HTLV-I). Journal of Emergency Medicine. 2000; 18(1): 109-19.
[2] Barmak K, Harhaj E, Grant C et al. Human T cell leukemia virus type I-induced disease: pathways to cancer and neurodegeneration. Virology. 2003; 308(1): 1-12.
[3] Yao J, Wigdahl B. Human T cell lymphotropic virus type I genomic expression and impact on intracellular signaling pathways during neurodegenerative disease and leukemia. Frontiers in Bioscience. 2000; 5: D138-68.
[4] Kannagi M, Harashima N, Kurihara K et al. Tumor immunity against adult T-cell leukemia. Cancer Science. 2005; 96(5): 249-55.
[5] Barmak K, Harhaj E, Grant C et al. Human T cell leukemia virus type I-induced disease: pathways to cancer and neurodegeneration. Virology. 2003; 308(1): 1-12.
[6] Poiesz BJ, Poiesz MJ, Choi D. The human T-cell lymphoma/leukemia viruses. Cancer Investigation. 2003; 21(2): 253-77.
[7] Barmak K, Harhaj E, Grant C et al. Human T cell leukemia virus type I-induced disease: pathways to cancer and neurodegeneration. Virology. 2003; 308(1): 1-12.
[8] Poiesz BJ, Papsidero LD, Ehrlich G et al. Prevalence of HTLV-I-associated T-cell lymphoma. American Journal of Hematology. 2001; 66(1): 32-8.