Originally isolated by Gallo from an African American patient, HTLV-1 has been shown to be associated with an adult T cell leukemia. A similar virus was isolated  in Japan from a patient with adult T cell leukemia (this virus was originally named adult T cell leukemia/lymphoma virus (ATLV)). ATLV and HTLV-1 are the same and the latter name is now used.  In the Caribbean area, the virus is  associated with a neuromyelopathy known as tropical spastic paraparesis and also with infective dermatitis. In Japan, there is a similar disease called HTLV-associated myelopathy. In Japan, HTLV-1 also is associated with uveitis. Other diseases associated with the virus are arthritis and polymyositis.

Tropical spastic paraparesis is a disease that affects the gray and white matter of the spinal cord (myelopathy). It is chronic and progressive and is an inflammatory disease. It results in the progressive spasticity of the legs, incontinence and constipation. About 1 - 4% of HTLV-1-infected patients develop slowly progressive  tropical spastic paraparesis but 10-15% of recently diagnosed patients in Peru and Brazil show rapid development of symptoms.

This virus is endemic to very specific regions of the globe:

South West Japan: Okinawa, Kiyushu, Shikoku (12 - 16% infection rate)
Caribbean (2 - 6% infection rate)
South America: Columbia, French Guyana, Brazil
Equatorial Africa: Gabon, Congo
Middle East: North eastern Iran
Melanesia

HTLV-1 is also found at a much higher rate than the general population in Australian Aboriginal people and Canadian Inuit people.

In all areas, seroprevalence increases with age, particularly among young women

Total world infected population: 15 - 20 million

Of these, 2 - 10% develop HTLV-associated disease

Transmission: