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Human T-cell lymphotrophic virus type-I (HTLV-I) is an exogenous human retrovirus that causes adult T cell leukemia (ATL) and a progressive neurological disorder, HTLV-I associated myelopathy/tropical spastic paraparesis (HAM/TSP). Most HTLV-I infected individuals are asymptomatic carriers. However, 0.25 - 3% infected individuals will develop HAM/TSP. HTLV-I integrated proviral genome is approximately 9 kb including gag, pol and env genes common to all cis-acting retroviruses. A cis-acting enhancer element has been detected within the gag gene of several avian retroviruses, including Rous sarcoma virus, Fujinami sarcoma virus, and the endogenous Rous-associated virus-0. A consensus enhancer core sequence, GTGGTTTG, is present in all of these viral genomes (citation: Arrigo S et al., Mol Cell Biol 1987). The above viral genes are flanked by long terminal repeat (LTR). Human T-cell lymphotrophic virus type-II (HTLV-II) is also an exogenous human retrovirus. Although rare, HTLV-II infection is associated with a chronic encephalomyelopathy similar to that of classic HTLV-I-associated HAM/TSP. In 2005, two new primate retroviruses were identified, Human T-cell lymphotrophic virus type-III (HTLV-III) and Human T-cell lymphotrophic virus type-IV (HTLV-IV), among individuals who hunt, butcher, or keep monkeys or apes as pets in southern Cameroon. However, it is still unknown whether these viruses are pathogenic and can be transmitted among humans. [ABSTRACT FROM AUTHOR]

An encyclopedia entry for "human T-cell leukemia virus (HTLV)" is presented. It refers to a human retrovirus that is associated with adult T cell leukemia and topical spastic paraparesis. HTLV-I is the most common type of HTLV and is consistently associated with diseases. HLTV may be present in many people without causing disease.

A definition of the term "HTLV-1 Tax" is presented. The term refers to a transactivating protein of region X. It is a transforming protein encoded by the X-region of the human T-cell lymphotropic virus type-1 (HTLV-1) genome. Tax trans-activates different cellular and viral promoters through interaction with cellular transcription factors.

A definition of the term "HTLV-1" is presented. The term, which stands for human T-cell lymphotropic virus type-1 (HTLV-1), is a human retrovirus. HTLV-1 is associated with a clinically aggressive form of adult T-cell leukemia and degenerative neuromuscular diseases like tropical spastic paraparesis.