Human T-lymphotropic virus 1

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Human T-lymphotropic virus 1
HTLV-1 and HIV-1 EM 8241 lores.jpg

HIV-1 and HTLV-1 in the EM .

Systematics
Classification : Viruses
Area : Riboviria
Empire : Pararnavirae
Phylum : Artverviricota
Class : Revtraviricetes
Order : Ortervirales
Family : Retroviridae
Subfamily : Orthoretrovirinae
Genre : Deltaretrovirus
Type : Primate T Lymphotrophic Virus 1
Subspecies : Human T-lymphotropic virus 1
Taxonomic characteristics
Genome : RNA
Baltimore : Group 6
Cover : available
Scientific name
Human T-lymphotropic virus 1
Left

The Human T lymphotropic virus 1 (HTLV-1) (formerly: Human T-cell leukemia virus 1 ) is a retrovirus , the human and other related primates to infect. It primarily infects CD4- positive T lymphocytes and can cause T cell leukemia or neurological diseases, particularly tropical spastic paraparesis , in a small minority of those infected .

Historical

HTLV-1 was discovered in 1979/1980 as the first human-pathogenic retrovirus by Robert Gallo's group at the NIH . This was preceded by a decade-long search for retroviruses in humans, after retroviruses from the animal kingdom had long been known. The discovery was accordingly a scientific sensation. Shortly thereafter, a second human retrovirus closely related to HTLV-1 was discovered, which was then named HTLV-2 . The first HTLV-1 virus isolates from patients with T-cell - leukemia . The name "HTLV" therefore initially stood for "human T-cell leukemia virus". It was later discovered that HTLV-1 can also cause other non- malignant diseases and the name was changed to "T-lymphotropic virus". In the years that followed, various retroviruses closely related to HTLV-1 and HTLV-2 were discovered in primates , which are then referred to as "simian T-lymphotropic viruses" or "prime T-lymphotropic viruses" (T-lymphotropic viruses from monkeys or monkeys). Primates). Today it is assumed that the human viruses HTLV-1 and HTLV-2 originated from the transmission of monkey retroviruses to humans within the last 20,000 years or so.

In 2005, two more retroviruses, closely related to HTLV-1 and -2, were discovered in bush game hunters in Cameroon , which were provisionally named HTLV-3 and HTLV-4. HTLV-3 (or HTLV-III) is also an outdated name from the 1980s for the HI virus .

Taxonomy

Taxonomically , HTLV-1 is counted among the delta retroviruses and, due to its close genetic relationship with the delta retroviruses of non-human primates, is divided into a common subgenus primate delta retroviruses .

Epidemiology

It is estimated that around 15–20 million people infected with HTLV-1 worldwide (for comparison: HIV : around 36 million in 2016). In contrast to HIV, the number of people infected has probably not changed significantly in the last few decades (according to estimates, exact figures do not exist for most countries). In contrast to HIV, which has spread explosively , especially in sub-Saharan Africa since the early 1980s, and has become a pandemic , HTLV-1 infections have largely remained limited to certain endemic areas . The reasons for this are probably the significantly less efficient transmission of HTLV-1 in contrast to HIV. Known endemic areas are:

However, there are no reliable figures for many countries. Concerning. Japan is believed that the virus was introduced into the country in the 16th century by Portuguese sailors and merchants who had a trading post in Nagasaki for many decades . The Portuguese, on the other hand, were likely infected through sexual contact in Africa. However, this hypothesis is controversial and cannot be considered proven. HTLV-1 is almost non-existent in Europe (with the exception of immigrants from endemic areas such as Caribbean immigrants in Great Britain ). In contrast to the USA, blood donors in Germany are usually not routinely tested for HTLV-1 due to their rarity.

genetics

The HTLV-1 genome consists of RNA and comprises approx. 8,500 bases (for comparison: the human genome approx. 3 billion base pairs). At the ends it consists of two identical flanking sequences (the so-called long terminal repeats ). In between are the three 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, however, HTLV-1 has other genes that code for proteins that influence the expression of virus genes and also cellular genes. At least one of these genes - tax - seems to be decisively involved in the malignant transformation of the infected cell and the development of T-cell leukemia.

Routes of infection

Three main routes of infection are known:

Associated diseases

HTLV-1 mainly causes two diseases:

These diseases only occur in a small proportion of those infected with HTLV-1. For example, there were more than one million people infected with HTLV-1 in Japan in the 1990s, but only between 500 and 1000 cases of ATL were observed annually. It is estimated that the lifelong risk of these diseases with infection is around 1–2% each. This is a major difference to HIV infection, in which practically 100% of those infected, if left untreated, will develop AIDS sooner or later .

In Japan, infection used to occur mainly perinatally through the breast milk of infected mothers. Since this mode of transmission has been known, there have been programs that encourage these mothers to abstain from breastfeeding . As a result, there has actually been a significant reduction in the rate of new infections in Japan. It is interesting that ATL usually occurs in older people (the average age of the sick is> 60 years). In the case of a predominantly perinatal infection, one must therefore assume an extremely long latency period for the virus (60 years and more). This is also a major difference to HIV, where the time between infection and development of AIDS is usually less than 10 years if no treatment is given. It must also be emphasized that adult T-cell leukemia is a very special form of T-cell leukemia that only occurs in HTLV-1 endemic areas. In Europe, where HTLV-1 hardly occurs, there are also T-cell leukemias, but these are not caused by HTLV-1.

HTLV-1 belongs together with the hepatitis B virus (HBV), the hepatitis C virus (HCV), the Epstein-Barr virus (EBV), the human papillomavirus (HPV) and the human herpes virus 8 (HHV- 8, also Kaposi's sarcoma herpes virus, KSHV) to a group of human carcinogenic viruses that are responsible for 10 to 15 percent of all cancers worldwide .

therapy

There is no known effective therapy for HTLV-1 infection. 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 wrong to assume that someone who has antibodies to HTLV-1 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.

The diseases ATL and TSP / HAM caused by HTLV-1 must be treated accordingly. For example, ATL is treated like leukemia. There is no antiviral therapy. The prognosis for the diseases is generally poor.

literature

  • Robert Gallo: The Hunt for the Virus - AIDS, Cancer and the Human Retrovirus. The story of its discovery. S. Fischer Verlag, Frankfurt am Main 1991, ISBN 3-10-024404-4 . (Gallo's scientific autobiography)
  • RC Gallo: The discovery of the first human retrovirus: HTLV-1 and HTLV-2. In: Retrovirology. 2005, 2, p. 17. (English-language review article, freely accessible in BioMed Central : full text )

Web links

Commons : Human T-lymphotropic virus 1  - Collection of pictures, videos and audio files

Individual evidence

  1. a b c d ICTV: ICTV Taxonomy history: Commelina yellow mottle virus , EC 51, Berlin, Germany, July 2019; Email ratification March 2020 (MSL # 35)
  2. SIB: Primate T-lymphotropic virus 1 , on: ViralZone
  3. BJ Poiesz, FW Ruscetti, AF Gazdar, PA Bunn, JD Minna, RC Gallo: Detection and isolation of type C retrovirus particles from fresh and cultured lymphocytes of a patient with cutaneous T-cell lymphoma. In: Proc Natl Acad Sci USA . 1980; 77, pp. 7415-7419. PMID 6261256 .
  4. VS Kalyanaraman, MG Sarngadharan, M. Robert-Guroff, I. Miyoshi, D. Golde, RC Gallo: A new subtype of human T-cell leukemia virus (HTLV-II) associated with a T-cell variant of hairy cell leukemia . In: Science . 1982; 218, pp. 571-573. PMID 6981847 .
  5. ^ S. Van Dooren, M. Salemi, AM Vandamme: Dating the origin of the African human T-cell lymphotropic virus type-i (HTLV-I) subtypes. In: Mol Biol Evol. 2001; 18, pp. 661-671. PMID 11264418 .
  6. R. Mahieux, A. Gessain: The human HTLV-3 and HTLV-4 retroviruses: New members of the HTLV family . In: Pathol. Biol. Band 57 , May 2008, p. 161 , doi : 10.1016 / j.patbio.2008.02.015 , PMID 18456423 ( elsevier.com ).
  7. D. Martin, JS Gutkind: Human tumor-associated viruses and new insights into the molecular mechanisms of cancer . In: Oncogene . tape 27 , no. 2 , 2008, p. 31-42 , PMID 19956178 .