Human T-lymphotropic virus 2
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The Human T lymphotropic virus 2 (HTLV-2) (formerly: Human T-cell leukemia virus 2 ) is a retrovirus , the human and other related primates to infect. It primarily infects CD8- positive T lymphocytes . The association of the virus with human diseases has not been clearly established. Maybe it leads a minority of infected persons to certain T-cell - lymphoma and neurological diseases.
Historical
HTLV-2 was discovered shortly after HTLV-1 was discovered in the early 1980s, as was this one in Robert Gallo's group at the National Institutes of Health (NIH). As stated in the first description, it was isolated from lymphocytes of a patient with a "T-cell variant of hairy cell leukemia ". Since hairy cell leukemia is by definition a B-cell - non-Hodgkin's lymphoma (there is no "T-cell variant"), it remains unclear which disease this patient was actually suffering from.
To date it has not been clearly established whether HTLV-2 causes human diseases. There are two main reasons for this: On the one hand, HTLV-2 infections are much rarer than HTLV-1 infections, and on the other hand, HTLV-2 infections in Western countries are predominantly found in intravenous drug addicts who often also carry other viruses infected (especially HIV ), so it is not entirely clear what role HTLV-2 plays in diseases.
Taxonomy
Taxonomically , HTLV-2, like HTLV-1, belongs to the genus Deltaretrovirus . In non-human primates , retroviruses have been discovered which are very similar to HTLV-2 and are accordingly referred to as Simian T-cell lymphotropic virus 2 (STLV-2). Today it is assumed that the human viruses HTLV-1 and -2 originated from the transmission of corresponding monkey retroviruses to humans many 1000 years ago.
Epidemiology
The number of people infected with HTLV-2 is unknown. The number of infected people is certainly significantly lower than with HTLV-1 (approx. 15-20 million worldwide) or even HIV (approx. 40 million worldwide). In western countries (especially the USA ) the virus is mainly found in drug addicts. It is interesting, however, that some relatively isolated indigenous peoples also have an extraordinarily high prevalence , e. B.
- Guahibo and Kayapó in the Amazon basin in Brazil or Venezuela
- Guaymí in Central America ( Panama )
- Melanesian populations on certain Pacific islands or in the highlands of Papua New Guinea
- Pygmies in Equatorial Africa .
The virus is practically non-existent in Europe . In contrast to the USA, blood donors in Germany are usually not routinely tested for HTLV-2 due to their rarity.
genetics
The HTLV-2 genome consists of RNA and comprises approx. 8500 bases (for comparison: the human genome approx. 3,000,000,000 base pairs). It shows a high degree of sequence homology with HTLV-1. During the replication cycle, the virus genome is transcribed into double-stranded DNA by the reverse transcriptase; it then has two identical flanking sequences (the so-called long terminal repeats ) at the ends . In between are the 3 gene regions typical of all retroviruses: gag (gene region for the virus structural proteins that make up the inner virus envelope), pol (virus enzymes , which are important for circumscribing the virus genome in DNA and integrating it into the cellular genome) and env (Virus proteins that are built into the outer virus envelope and are crucial for which cells the virus can infect).
In addition, HTLV-2 has other genes that code for proteins that influence the expression of viral genes and also cellular genes. It is possible that one of these genes - tax - is causally involved in the development of human diseases.
Routes of infection
Three main routes of infection are known:
- perinatal infection of the infant through the breast milk of infected mothers
- through transfusion of infected blood products
- through sexual contact .
Associated diseases
The association with human diseases has not been clearly established. There have been sporadic reports of T-cell lymphomas and neurological diseases in infected people, but no reliable causal chain has yet been established. At least it seems to be the case that the virus leads to a significantly increased mortality in virus carriers.
therapy
An effective therapy for HTLV-2 infection is not known. In the event of an infection, the virus persists in the organism for life and can usually no longer be eliminated by the immune system (the virus genome is incorporated into the genome of the infected cell during infection). It is therefore a mistake to assume that someone who has antibodies to HTLV-2 in the blood is immune to this virus . On the contrary, the antibodies show that the person affected has had contact with the virus and is permanently infected (just like with HIV). An effective vaccination against the virus does not yet exist.
literature
- Robert Gallo The Hunt for the Virus - AIDS, Cancer and the Human Retrovirus. The story of its discovery. S. Fischer Verlag, Frankfurt / Main, 1991, ISBN 3-10-024404-4 (his scientific autobiography)
- Gallo RC The discovery of the first human retrovirus: HTLV-1 and HTLV-2. Retrovirology 2005, 2:17 (English-language review article, freely accessible in BioMed Central : full text )
- Kalyanaraman VS, Sarngadharan MG, Robert-Guroff M, Miyoshi I, Golde D, Gallo RC. A new subtype of human T-cell leukemia virus (HTLV-II) associated with a T-cell variant of hairy cell leukemia. Science 1982; 218: 571-573. (PubMed: 6981847, first description)
- Orland JR, Wang B, Wright DJ, Nass CC, Garratty G, Smith JW, Newman B, Smith DM, Murphy EL; HOST Investigators. Increased mortality associated with HTLV-II infection in blood donors: a prospective cohort study. Retrovirology. 2004 Mar 24; 1 (1): 4 (PubMed: 15169553)
Individual evidence
- ↑ a b c d ICTV: ICTV Taxonomy history: Commelina yellow mottle virus , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
- ↑ SIB: Primate T-lymphotropic virus 2 , on: ViralZone
