Human T-cell leukemia virus (HTLV)
Human T-cell leukemia virus (HTLV) is a retrovirus that is classified into four types: HTLV-1, HTLV-2, HTLV-3, and HTLV-4. Of these, HTLV-1 is the most significant, as it is associated with serious health conditions, including adult T-cell leukemia (ATLL) and adult T-cell lymphoma (ATL), as well as HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). While many individuals infected with HTLV-1 remain asymptomatic, about 5% may develop severe diseases that can lead to mortality. The virus is primarily transmitted through sexual contact, breastfeeding, blood transfusions, and intravenous drug use. HTLV-1 is most commonly found in regions such as Japan and Central Africa, with distinct subtypes prevalent in different geographical areas.
Historically, HTLV-1 was discovered in 1977 and is noted for being the first identified human retrovirus, playing a role in certain cancers alongside other viruses like HIV and HPV. The effective management of HTLV-1 includes antibody screening in blood donations and specific methods to prevent mother-to-child transmission during breastfeeding. Understanding HTLV is crucial for public health, especially in areas where the virus is endemic, as it poses significant health risks to affected populations.
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Subject Terms
Human T-cell leukemia virus (HTLV)
ALSO KNOWN AS: Human T-lymphotropic virus, adult T-cell lymphoma virus; HTLV-1 may also be called human T-cell lymphotropic virus type 1 or adult T-cell lymphoma virus type 1
RELATED CANCERS: Adult T-cell leukemia (ATLL), adult T-cell lymphoma (ATL), HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP)
DEFINITION: Human T-lymphotropic virus is a retrovirus grouped into four types—human T-lymphotropic virus 1, 2, 3, or 4. Although HTLV-2, 3, and 4 occur in humans, they have not been clearly identified as the causative agent for a specific disease. However, infection with the HTLV-1 virus may result in adult T-cell lymphoma/adult T-cell leukemia (ATL), HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), loss of spinal nerve function, uveitis, and other inflammatory disorders.
Exposure routes: Sexual transmission, breastfeeding, blood transfusions, intravenous drug use, organ or tissue transplants
Where found: The HTLV-1 virus is most endemic in Japan, primarily the HTLV-1 Subtype A (cosmopolitan subtype). Subtypes B, D, and F are prevalent in Central Africa, and in Melanesia, Subtype C is the most common. In South and Central Africa, Subtype E is common.
At risk: Five to ten million people worldwide are infected with the HTLV-1 virus, though a lack of reliable data may skew these estimates. The freeze-thaw method is effective in preventing the transmission of the virus from mother to child in breast milk. Antibody screening in all blood and tissue donations is important in lowering the transmission rate.
Etiology and symptoms of associated cancers: T cells are central to cell-mediated immunity. T cells originate in the bone marrow and mature in the thymus, where they acquire surface markers, to distinguish self from non-self. The HTLV-1 virus takes up residence by infecting a subset of the T cells called CD4+ helper cells. Though 95 percent of individuals infected with HTLV-1 have no symptoms, about 5 percent of patients experience potentially fatal disease. Once there, they grow continuously, turn on specific genes, and evolve into leukemic cells that spread through the body. The resulting leukemia is classified as acute, lymphomatous, chronic, or smoldering. The acute and lymphomatous forms have a poor prognosis, with survival rates averaging less than one year.
History: Following interspecies transmission, this virus diverged from its simian prototype about fifty thousand years ago in Africa. Discovered in 1977 as the causative agent for adult T-cell leukemia, this virus was the first identified human retrovirus. In 1980, Robert C. Gallo and Bernard J. Poiesz confirmed the virus’s infectivity, resulting in response and presence in a patient with T-cell cancer. HTLV-1 is among the known viruses that cause cancer, along with human immunodeficiency virus (HIV), human papillomavirus (HVP), and hepatitis B virus (HBV).
Bibliography
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