|- valign=top |Species:||Human T-lymphotropic virus 2

|- valign=top |Species:||Human T-lymphotropic virus 3

|- valign=top |Species:||Human T-lymphotropic virus 4 Human T-lymphotropic virus (HTLV) is a human, single-stranded RNA retrovirus that causes T-cell leukemia and T-cell lymphoma in adults and may also be involved in certain demyelinating diseases.

HTLV-I

HTLV-I is an abbreviation for the human T-cell leukemia virus type 1, also called the human T-cell lymphotrophic virus type 1, a virus that has been seriously implicated in several kinds of diseases including HTLV-I-associated myelopathy and a virus cancer link for leukemia: see adult T-cell leukemia/lymphoma. Between one in twenty and one in twenty-five infected persons are thought to develop cancer as a result of the virus.

Infection with HTLV-I, like infection with other retroviruses, probably occurs for life and can be inferred when antibody against HTLV-1 is detected in the serum. HTLV-I infection in the United States appears to be about half as prevalent as HIV infection among IV drug users and about one-tenth as prevalent in the population at large. Although little serologic data exist, prevalence of infection is thought to be highest among blacks living in the Southeast. A prevalence rate of 30% has been found among black intravenous drug abusers in New Jersey, and a rate of 49% has been found in a similar group in New Orleans. It is possible that prevalence of infection is increasing in this risk group.

Studies of HTLV-I antibody indicate that the virus is endemic in southern Japan, in the Caribbean, and in Africa.

Transmission of HTLV-I is believed to occur from mother to child; by sexual contact; and through exposure to contaminated blood, either through blood transfusion or sharing of contaminated needles. The importance of the various routes of transmission is believed to vary geographically. In Japan, the geographic clustering of infection and the rarity of unprotected sexual contact suggest that the virus is more dependant on mother-to-child transmission. In the Carribean, the geographic distribution of the virus is more uniform, and it is more common among those with many sexual partners, indicating that sexual transmission is more common.

The time between infection and onset of cancer also varies geographically. It is believed to be about sixty years in Japan, and less than forty years in the Carribean.

HTLV-II

A virus closely related to HTLV-I, HTLV-II shares 60% genomic homology (structural similarity) with HTLV-I. It is found predominantly in IV drug users and Native Americans, as well as Caribbean and South American Indian groups. HTLV-II has not been clearly been linked to any disease, but has been associated with several cases of myelopathy/tropical spastic paraparesis (HAM/TSP )-like neurological disease.

HTLV-III and HTLV-IV

These viruses were discovered in 2005 in rural Cameroon, and were apparently transmitted from monkeys to hunters of monkeys through bites and scratches. HTLV-III is similar to STLV-III (Simian T-lymphotropic virus 3 ), but 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 name HTLV-III was sometimes applied to HIV in the early literature, but has since fallen out of use.

References

Cantor et al., 1991. HTLV I/II seroprevalence and HIV/HTLV coinfection among United States intravenous drug users. J. Acquired Immune Defic Syndr. 4, 460-7.

Clark J. et al., 1985. Seroepidemiologic studies of human T-cell leukemia/lymphoma virus type I in Jamaica. Int. J. Cancer 36, 37-41.

Ewald, Paul W. Evolution of Infectious Disease. New York: Oxford UP, 1994.

Tajima, K. 1988. The T-and B-cell malignancy study group. The third nation-wide study on adult T-cell leukemia and lymphoma (ATL) in Japan: Characteristic patterns of HLA antigen and HTLV-1 infection in ATL patients and their relatives. Int. J. Cancer 41, 505-12.

External links

• eMedicine's human T-cell lymphotrophic virus webpage
• New York Times: Two New Viruses Reported Belonging to AIDS Family