Human T-lymphotropic virus 2

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Human T-lymphotropic virus 2
Specialty Infectious diseases
Symptoms Mild cognitive Impairment, Mycosis fungoides
DurationChronic, incurable
CausesHTLV-2
Risk factors Unsafe sex, haemophiliacs
Diagnostic method Blood test
Differential diagnosis HIV/AIDS, Lymphoma, HTLV-1
PreventionPracticing safe-sex, use of clean needles, screening blood transfusions, Avoiding breastfeeding.
Medication Antiretrovirals, chemotherapy
Prognosis 95% present with no symptoms, generally good
Frequency15-20 million people worldwide
Primate T-lymphotropic virus 2
Virus classification Red Pencil Icon.png
(unranked): Virus
Realm: Riboviria
Kingdom: Pararnavirae
Phylum: Artverviricota
Class: Revtraviricetes
Order: Ortervirales
Family: Retroviridae
Genus: Deltaretrovirus
Species:
Primate T-lymphotropic virus 2

A virus closely related to HTLV-I, human T-lymphotropic virus 2 (HTLV-II) shares approximately 70% genomic homology (structural similarity) with HTLV-I. It was discovered by Robert Gallo and colleagues. [1] [2]

Contents

HTLV-2 is prevalent among the indigenous populations in Africa and the Indian-American tribes in Central and South America as well as among drug users in Europe and North America [3] It can be passed down from mother to child through breastmilk and genetically as well from either parent.

HTLV-II entry in target cells is mediated by the glucose transporter GLUT1. [4]

A phylogeny of the subtypes of HTLV and their relationships between endogenous and exogenous retroviruses in the human genome. HERV = human endogenous retrovirus, SFV = simian foamy virus HTLV Phylogeny.jpg
A phylogeny of the subtypes of HTLV and their relationships between endogenous and exogenous retroviruses in the human genome. HERV = human endogenous retrovirus, SFV = simian foamy virus

Virology

HTLV-1 and HTLV-2 share broad similarities in their overall genetic organization and expression pattern, but they differ substantially in their pathogenic properties. [3] The virus utilizes the GLUT-1 and NRP1 cellular receptors for their entry, although HTLV-1, but not HTLV-2, is dependent on heparan sulfate proteoglycans. Cell-to-cell transmission is essential for virus replication and occurs through the formation of a virological synapse. [3] The family of Human T-lymphotropic virus (Figure 2) can be further categorized into four sub types. The figure also divides the retroviruses into exogenous and endogenous. Retroviruses can exist as two different forms: endogenous which consist of normal genetic components and exogenous which are horizontally transferred genetic components that are usually infectious agents that cause disease i.e. HIV. In (Figure 3) open reading frames (ORF) are shown which can if translated can predict which genes will be present and this can help to better understand human retroviruses. Of the four subtypes, HTLV-2 may be linked to Cutaneous T-cell lymphoma (CTCL). [5] In one study involving cultured lymphocytes from patients with mycosis fungoides (Figure 1), PCR amplification showed gene sequences of HTLV-II. This finding may suggest a possible correlation with HTLV-2 and CTCL. Further research and studies must be conducted to show a positive relationship. [1]

Transmission

Perinatal transmission and breastfeeding and through blood transfusion, sexual contact, and use of intravenous drugs. [3]

Epidemiology

HTLV-1 and HTLV-2 are both involved in actively spreading epidemics, affecting 15-20 million people worldwide. [4] In the United States, the overall prevalence is 22 per 100,000 population, with HTLV-2 more common than HTLV-1. Data collection performed from 2000 to 2009 among US blood donors has shown a general decline since the 1990s. [6]

Symptoms

Human T- leukemia, type 2 (HTLV-2) generally causes no signs or symptoms. Although HTLV-2 has not been definitively linked with any specific health problems, scientists suspect that some affected people may later develop neurological problems such as: [7] [6]

Figure 1. Mycosis fungoides, a skin disease showing nodules and plaques composed of lymphocytes spread across the skin, has been associated with HTLV-II infection Neck of a woman suffering from mycosis fungoides of the skin Wellcome L0061976.jpg
Figure 1. Mycosis fungoides , a skin disease showing nodules and plaques composed of lymphocytes spread across the skin, has been associated with HTLV-II infection

Although evidence is limited, there may also be a link between HTLV-2 and chronic lung infections (i.e. pneumonia and bronchitis), asthma and dermatitis. [8]

Clinical significance

HTLV-II has not been clearly linked to any disease, but has been associated with several cases of myelopathy/tropical spastic paraparesis (HAM/TSP)- like neurological disease and may cause chronic lung problems. [ citation needed ]

An impact on platelet count has been observed. [9]

In the 1980s, HTLV-2 was identified in a patient with an unidentified T cell lymphoproliferative disease that was described as having characteristics similar to the B cell disorder, hairy cell leukemia. [10] HTLV-2 was identified in a second patient with a T cell lymphoproliferative disease; this patient later developed hairy cell leukemia, but HTLV-2 was not found in the hairy cell clones. [11] The cause of hairy cell leukemia is not known, but it is no longer believed to be related to viral infections.[ citation needed ]

Treatment

There are few treatments [12] including chemotherapy and antiretrovirals that can slow the viral load but no cure or definitive treatment exists for HTLV-2. [8]

Diagnosis

Human T- leukemia, type 2 (HTLV-2) is usually diagnosed based on blood tests that detect to the virus. However, HTLV-2 is often never suspected or diagnosed since most people never develop any signs or symptoms of the infection. Diagnosis may occur during  for blood donation, testing performed due to an infection, or a work-up for an HTLV-2-associated medical problems. [8]

Prevention

Due to there being no cure for HTLV II the prevention is focused on early detection and preventing the spread of HTLV-2 to others.  blood donors, promoting safe sex and discouraging needle sharing can decrease the number of new infections. Mother-to-child transmission can be reduced by screening pregnant women so infected mothers can avoid breastfeeding. [8]

Prognosis

The long-term outlook for most people infected with HTLV-2 is good. Infection with HTLV-2 is lifelong, but 95% of affected people have no signs or symptoms of the condition. Although, HTLV-2-related health problems tend to be significantly milder than those associated with HTLV1. [8]

Related Research Articles

<span class="mw-page-title-main">Leukemia</span> Blood cancers forming in the bone marrow

Leukemia is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called blasts or leukemia cells. Symptoms may include bleeding and bruising, bone pain, fatigue, fever, and an increased risk of infections. These symptoms occur due to a lack of normal blood cells. Diagnosis is typically made by blood tests or bone marrow biopsy.

<span class="mw-page-title-main">Retrovirus</span> Family of viruses

A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase enzyme to produce DNA from its RNA genome, the reverse of the usual pattern, thus retro (backwards). The new DNA is then incorporated into the host cell genome by an integrase enzyme, at which point the retroviral DNA is referred to as a provirus. The host cell then treats the viral DNA as part of its own genome, transcribing and translating the viral genes along with the cell's own genes, producing the proteins required to assemble new copies of the virus.

<span class="mw-page-title-main">Human T-lymphotropic virus 1</span> Species of virus

Human T-cell lymphotropic virus type 1 or human T-lymphotropic virus (HTLV-I), also called the adult T-cell lymphoma virus type 1, is a retrovirus of the human T-lymphotropic virus (HTLV) family that has been implicated in several kinds of diseases including very aggressive adult T-cell lymphoma (ATL), HTLV-I-associated myelopathy, uveitis, Strongyloides stercoralis hyper-infection and some other diseases. It is thought that about 1–5% of infected persons develop cancer as a result of the infection with HTLV-I over their lifetimes.

<span class="mw-page-title-main">Hairy cell leukemia</span> Hematological malignancy

Hairy cell leukemia is an uncommon hematological malignancy characterized by an accumulation of abnormal B lymphocytes. It is usually classified as a subtype of chronic lymphocytic leukemia (CLL). Hairy cell leukemia makes up about 2% of all leukemias, with fewer than 2,000 new cases diagnosed annually in North America and Western Europe combined.

<span class="mw-page-title-main">Adult T-cell leukemia/lymphoma</span> Human disease

Adult T-cell leukemia/lymphoma is a rare cancer of the immune system's T-cells caused by human T cell leukemia/lymphotropic virus type 1 (HTLV-1). All ATL cells contain integrated HTLV-1 provirus further supporting that causal role of the virus in the cause of the neoplasm. A small amount of HTLV-1 individuals progress to develop ATL with a long latency period between infection and ATL development. ATL is categorized into 4 subtypes: acute, smoldering, lymphoma-type, chronic. Acute and Lymphoma-type are known to particularity be aggressive with poorer prognosis.

<span class="mw-page-title-main">Oncovirus</span> Viruses that can cause cancer

An oncovirus or oncogenic virus is a virus that can cause cancer. This term originated from studies of acutely transforming retroviruses in the 1950–60s, when the term "oncornaviruses" was used to denote their RNA virus origin. With the letters "RNA" removed, it now refers to any virus with a DNA or RNA genome causing cancer and is synonymous with "tumor virus" or "cancer virus". The vast majority of human and animal viruses do not cause cancer, probably because of longstanding co-evolution between the virus and its host. Oncoviruses have been important not only in epidemiology, but also in investigations of cell cycle control mechanisms such as the retinoblastoma protein.

<span class="mw-page-title-main">Cutaneous T-cell lymphoma</span> Medical condition

Cutaneous T-cell lymphoma (CTCL) is a class of non-Hodgkin lymphoma, which is a type of cancer of the immune system. Unlike most non-Hodgkin lymphomas, CTCL is caused by a mutation of T cells. The cancerous T cells in the body initially migrate to the skin, causing various lesions to appear. These lesions change shape as the disease progresses, typically beginning as what appears to be a rash which can be very itchy and eventually forming plaques and tumors before spreading to other parts of the body.

<span class="mw-page-title-main">Tropical spastic paraparesis</span> Medical condition

Tropical spastic paraparesis (TSP), is a medical condition that causes weakness, muscle spasms, and sensory disturbance by human T-lymphotropic virus resulting in paraparesis, weakness of the legs. As the name suggests, it is most common in tropical regions, including the Caribbean. Blood transfusion products are screened for human T-lymphotropic virus 1 (HTLV-1) antibodies, as a preventive measure.

<span class="mw-page-title-main">T-cell lymphoma</span> Medical condition

T-cell lymphoma is a rare form of cancerous lymphoma affecting T-cells. Lymphoma arises mainly from the uncontrolled proliferation of T-cells and can become cancerous.

Viral vectors are tools commonly used by molecular biologists to deliver genetic material into cells. This process can be performed inside a living organism or in cell culture. Viruses have evolved specialized molecular mechanisms to efficiently transport their genomes inside the cells they infect. Delivery of genes or other genetic material by a vector is termed transduction and the infected cells are described as transduced. Molecular biologists first harnessed this machinery in the 1970s. Paul Berg used a modified SV40 virus containing DNA from the bacteriophage λ to infect monkey kidney cells maintained in culture.

A Tax Gene Product (Tax) is a nuclear protein that has a molecular weight of about 37,000 to 40,000 daltons.

<span class="mw-page-title-main">Xenotropic murine leukemia virus–related virus</span> Species of virus

Xenotropic murine leukemia virus–related virus (XMRV) is a retrovirus which was first described in 2006 as an apparently novel human pathogen found in tissue samples from men with prostate cancer. Initial reports erroneously linked the virus to prostate cancer and later to chronic fatigue syndrome (CFS), leading to considerable interest in the scientific and patient communities, investigation of XMRV as a potential cause of multiple medical conditions, and public-health concerns about the safety of the donated blood supply.

Bovine leukemia virus (BLV) is a retrovirus which causes enzootic bovine leukosis in cattle. It is closely related to the human T‑lymphotropic virus type 1 (HTLV-I). BLV may integrate into the genomic DNA of B‑lymphocytes as a DNA intermediate, or exist as unintegrated circular or linear forms. Besides structural and enzymatic genes required for virion production, BLV contains an oncogene coding for a protein called Tax and expresses microRNAs of unknown function. In cattle, most infected animals are asymptomatic; leukemia is rare, but lymphoproliferation is more frequent (30%).

<span class="mw-page-title-main">Robert Gallo</span> American biomedical researcher

Robert Charles Gallo is an American biomedical researcher. He is best known for his role in establishing the human immunodeficiency virus (HIV) as the infectious agent responsible for acquired immune deficiency syndrome (AIDS) and in the development of the HIV blood test, and he has been a major contributor to subsequent HIV research.

<span class="mw-page-title-main">Human T-lymphotropic virus</span> Informal grouping of virus species

The human T-lymphotropic virus, human T-cell lymphotropic virus, or human T-cell leukemia-lymphoma virus (HTLV) family of viruses are a group of human retroviruses that are known to cause a type of cancer called adult T-cell leukemia/lymphoma and a demyelinating disease called HTLV-1 associated myelopathy/tropical spastic paraparesis (HAM/TSP). The HTLVs belong to a larger group of primate T-lymphotropic viruses (PTLVs). Members of this family that infect humans are called HTLVs, and the ones that infect Old World monkeys are called Simian T-lymphotropic viruses (STLVs). To date, four types of HTLVs and four types of STLVs have been identified. HTLV types HTLV-1 and HTLV-2 viruses are the first retroviruses discovered. Both belong to the oncovirus subfamily of retroviruses and can transform human lymphocytes so that they are self-sustaining in vitro. The HTLVs are believed to originate from interspecies transmission of STLVs. The HTLV-1 genome is diploid, composed of two copies of a single-stranded RNA virus whose genome is copied into a double-stranded DNA form that integrates into the host cell genome, at which point the virus is referred to as a provirus. A closely related virus is bovine leukemia virus BLV. The original name for HIV, the virus that causes AIDS, was HTLV-3.

There are several forms of Epstein–Barr virus (EBV) infection. These include asymptomatic infections, the primary infection, infectious mononucleosis, and the progression of asymptomatic or primary infections to: 1) any one of various Epstein–Barr virus-associated lymphoproliferative diseases such as chronic active EBV infection, EBV+ hemophagocytic lymphohistiocytosis, Burkitt's lymphoma, and Epstein–Barr virus positive diffuse large B-cell lymphoma, not otherwise specified); 2) non-lymphoid cancers such as Epstein–Barr virus associated gastric cancer, soft tissue sarcomas, leiomyosarcoma, and nasopharyngeal cancers; and 3) Epstein–Barr virus-associated non-lymphoproliferative diseases such as some cases of the immune disorders of multiple sclerosis and systemic lupus erythematosis and the childhood disorders of Alice in Wonderland Syndrome and acute cerebellar ataxia.

<span class="mw-page-title-main">William A. Haseltine</span> American biologist (born 1944)

William A. Haseltine is an American scientist, businessman, author, and philanthropist. He is known for his groundbreaking work on HIV/AIDS and the human genome.

Simian-T-lymphotropic viruses, also Simian T-cell leukemia viruses (STLVs), are retroviruses closely related to the human sexually and breastfeeding transmissible viruses HTLV. They have subtypes 1 through 4 as compared to HTLV 1 through 4, and each subtype has its own serovars. Together they comprise PTLVs A study has shown that STLV-1 Tax and SBZ proteins have similar functions to their counterparts of HTLV-1. STLV-1 is oncogenic in Japanese macaques.

<span class="mw-page-title-main">Global Virus Network</span> International group of medical virologists

The Global Virus Network (GVN) is an international coalition of medical virologists whose goal is to help the international medical community by improving the detection and management of viral diseases. The network was founded in 2011 by Robert Gallo in collaboration with William Hall and Reinhard Kurth, and 24 countries were members of the network as of 2015. The GVN fosters research into viruses that cause human disease to promote the development of diagnostics, antiviral drugs and vaccines, and its mission includes strengthening scientific training and response mechanisms to viral outbreaks. The GVN has organized task forces for chikungunya, human T-lymphotropic virus, and Zika. The network is headquartered at the Institute of Human Virology at the University of Maryland School of Medicine, and Gallo serves as its scientific director.

William W. Hall is the chair of medical microbiology and professor emeritus at the Centre for Research in Infectious Diseases at University College Dublin.

References

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