Human T-lymphotropic virus

The Human T-lymphotropic virus Type I (HTLV-1) is a human RNA retrovirus that is known to cause a type of cancer, referred to as adult T-cell leukemia and lymphoma, and a demyelinating disease called HTLV-I associated myelopathy/Tropical spastic paraparesis (HAM/TSP). HTLV-I is one of a group of closely related primate T lymphotropic viruses (PTLVs). Members of this family that infect humans are called Human T-lymphotropic viruses, and the ones that infect old-world primates are called Simian T-lymphotropic viruses. To date, four types of HTLVs (HTLV-I, HTLV-II, HTLV-III, and HTLV-IV) and four types of STLVs (STLV-I, STLV-II, STLV-III, and STLV-V) have been identified. The HTLVs are believed to originate from intraspecies transmission of STLVs. The original name for HIV, the virus that causes AIDS, was HTLV-III; this term is no longer in use. The HTLV-1 genome is diploid, composed of two copies of a single-stranded RNA virus whose genome is copied into a double-stranded DNA form that integrates into the host cell genome, at which point the virus is referred to as a provirus. A closely related virus is bovine leukemia virus BLV.

HTLV-I
HTLV-I is an abbreviation for the human T-cell lymphotropic virus type 1, also called the Adult T-cell lymphoma virus type 1, a virus that has been seriously implicated in several kinds of diseases, including HTLV-I-associated myelopathy and Strongyloides stercoralis, and as a virus cancer link for leukemia (see adult T-cell leukemia/lymphoma). Between 1 in 20 and 1 in 25 infected persons are thought to develop cancer as a result of the virus.

HTLV-II
A virus closely related to HTLV-I, HTLV-II shares approximately 70% genomic homology (structural similarity) with HTLV-I.

HTLV-III and HTLV-IV
When HIV, the virus that causes AIDS, was characterized in 1984 by Robert Gallo  and Luc_Montagnier, it was originally named HTLV-III. HTLV-III is currently the name used to describe another virus related to HTLV-I and HTLV-II. "HTLV-IV" has been used to describe recently characterized viruses.

These viruses were discovered in 2005 in rural Cameroon, and were, it is presumed, transmitted from monkeys to hunters of monkeys through bites and scratches.


 * HTLV-III is similar to STLV-III (Simian T-lymphotropic virus 3). Multiple strains have been identified. It expresses gag, pol, and env, among other proteins.


 * HTLV-IV does not resemble any known virus.

It is not yet known how much further transmission has occurred among humans, or whether the viruses can cause disease.

The use of these names can cause some confusion, because the name HTLV-III was the former name of HIV in early AIDS literature, but has since fallen out of use. The name HTLV-IV has also been used to describe HIV-2.

Transmission
HTLV-I and HTLV-II are sexually transmitted.