Human T-cell Leukemia Virus 1 & 2.

This presentation was prompted by the requirement for pre-transplant donors to be screened for HTLV 1 & 2. It is meant as a brief, high-level overview of these viruses and is in no way a comprehensive review of the subject. It was given to the technical staff of the LLSG microbiology laboratory.

Introduction:

Human T-cell lymphotropic virus (HTLV) is one of the human retroviruses. Type one was discovered by Gallo and his colleagues in 1980 and shortly thereafter, 1982, a second HTLV was discovered. These became known as HTLV 1 and HTLV 2. HIV was at first classified as an HTLV and initially given the type 3 designation but was then found to be sufficiently different to warrant a new name and human immunodeficiency virus (HIV) is the name that has persistent

HTLV 1 & 2 are classified in the family Retroviridae day. They are single stranded RNA viruses that possess a reverse transcriptase. If humans are infected the virus inserts itself into the host genome and persists lifelong. It is able to evade the human immune system.

Disease Associations:

HTLV 1. Adult T-cell leukemia/lymphoma. Also a rare myelopathy, tropical spastic paraparesis. There it is also good evidence for this virus causing an infective dermatitis in children as well as a uveitis. HTLV 1 has also been implicated in a myriad of other diseases but few if any of these are good candidates to be caused by this virus.
HTLV 2 has not been linked convincingly to any disease state.

Modes of transmission:

The major modes of transmission are sexual contact, although type 2 may be poorly transmitted by this route. Breast-feeding. Blood transfusions, although this route has been virtually eliminated in countries who screen donated blood for these viruses prior to transfusion. IV drug abuser abusers transmit both types by sharing equipment but there is currently an epidemic of HTLV 2 too in the IVDU communities in Europe, North America, Southeast Asia and Australia.

Distribution pattern:

HTLV 1 has a worldwide distribution, with an estimated 15 to 20 million people infected. There are some regions in the world that have high prevalence rates. These include Southern Japan, the Caribbean and tropical Africa.

HTLV 2 was originally thought to have originated in the New World having been brought by human migrations 10 to 20,000 years ago. However it is found in the oldest known human ethnic group, the Pygmy group in central Africa. Interestingly the only known focus of Simian TLV 2 is also in central Africa.
As mentioned HTLV 2 has a high prevalence rates in IVDU. An informative map showing the distribution of both simian and human LTV 1 & 2 is included in the slide presentation.

Where did HTLV 1 & 2 originate from?

Primates also have variants of these viruses, called, Simian T-cell Lymphotropic Virus (STLV) it also occurs as type 1 and type 2. These primate viruses are likely human precursors and probably adapted to humans many mille