retrovirus

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retrovirus,

type of RNA virusvirus,
parasite with a noncellular structure composed mainly of nucleic acid within a protein coat. Most viruses are too small (100–2,000 Angstrom units) to be seen with the light microscope and thus must be studied by electron microscopes.
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 that, unlike other RNA viruses, reproduces by transcribing itself into DNA. An enzyme called reverse transcriptase allows a retrovirus's RNA to act as the template for this RNA-to-DNA transcription. The resultant DNA inserts itself into a cell's DNA and is reproduced along with the cell and its daughters. The life cycle is completed when the viral DNA in selected daughter cells makes an RNA copy of itself that covers itself in a protein coat and leaves the cell. Retroviruses sometimes destroy the cells whose DNA they alter, as with HIV, the virus that causes AIDSAIDS
or acquired immunodeficiency syndrome,
fatal disease caused by a rapidly mutating retrovirus that attacks the immune system and leaves the victim vulnerable to infections, malignancies, and neurological disorders. It was first recognized as a disease in 1981.
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, and sometimes cause them to become cancerous, as with the viruses that cause certain leukemiasleukemia
, cancerous disorder of the blood-forming tissues (bone marrow, lymphatics, liver, spleen) characterized by excessive production of immature or mature leukocytes (white blood cells; see blood) and consequently a crowding-out of red blood cells and platelets.
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. Lentiviruses are retroviruses that cause slowly progressing diseases, such as AIDS.

Retrovirus

A family of viruses distinguished by three characteristics: (1) genetic information in ribonucleic acid (RNA); (2) virions possess the enzyme reverse transcriptase; and (3) virion morphology consists of two proteinaceous structures, a dense core and an envelope that surrounds the core. Some viruses outside the retrovirus family have some of these characteristics, but none has all three. Numerous retroviruses have been described; they are found in all families of vertebrates. See Animal virus, Reverse transcriptase, Ribonucleic acid (RNA)

The genome is composed of two identical molecules of single-stranded RNA, which are similar in structure and function to cellular messenger RNA. Deoxyribonucleic acid (DNA) is not present in the virions of retroviruses. The reverse transcriptase in each virus makes a DNA copy of the RNA genome shortly after entry of the virus into the host cell. The discovery of this enzyme changed thinking in biology. Previously, the only known direction for the flow of genetic information was from DNA to RNA, yet retroviruses make DNA copies of their genome by using an RNA template. This reversal of genetic information was considered backward and hence the family name retrovirus, meaning backward virus.

Once the DNA copy of the RNA genome is made, it is inserted directly into one of the chromosomes of the host cell. This results in new genetic information being acquired by the host species. The study of reverse transcriptase has led to other discoveries of how retroviruses add a variety of new genetic information into the host. One such class of genes carried by retroviruses is oncogenes, meaning tumor genes. Retroviral oncogenes appear to be responsible for tumors in animals. See Oncogenes, Virus classification

Two distinct retroviruses have been discovered in humans. One is human T-cell lymphotropic virus type 1 (HTLV-1), a type C-like virus associated with adult T-cell leukemia. The other is the human acquired immune deficiency syndrome (AIDS) virus, a type E lentivirus. See Acquired immune deficiency syndrome (AIDS)

retrovirus

[′re·trō‚vī·rəs]
(virology)
A family of ribonucleic acid viruses distinguished by virions which possess reverse transcriptase and which have two proteinaceous structures, a dense core, and an envelope that surrounds the core.

retrovirus

A virus that is designed to avoid discovery by attacking the virus signatures or the antivirus program attempting to detect it. See virus and antivirus program.
References in periodicals archive ?
Vlahov, "Use of Sterile Syringes and Aseptic Drug Preparation Are Important Components of HIV Prevention among Injection Drug Users," Journal of Acquired Immune Deficiency Syndromes and Human Retrovirology, vol.
address correspondence to this author at: National HIV Immunology Laboratory, National HIV and Retrovirology Laboratories, Centre for Infectious Disease Prevention and Control, Bldg.
Everall said at the meeting, which was sponsored by the Foundation for Retrovirology and Human Health and the CDC.
That compared with only 23% of 91 placebo-treated patients whose viral loads dropped below that level, he said at the conference, which was sponsored by the Foundation for Retrovirology and Human Health.
The source patient's CD4 count did not affect the number of prophylactic drugs recommended to health care workers, she said at the meeting, sponsored by the Foundation for Retrovirology and Human Health.
LTC Brown is chief, Department of Retrovirology, at the Armed Forces Research Institute for Medical Sciences in Bangkok.
Powderly said at the meeting, which was sponsored by the Foundation for Retrovirology and Human Health and the CDC.
The data should help medical and public health officials allocate resources, he said at the meeting, sponsored by the Foundation for Retrovirology and Human Health.
The study was powered to detect at least a tripling of the complication rate in HIV-positive patients, compared with controls, he said at the conference, sponsored by the Foundation for Retrovirology and Human Health.
JS Epstein, MD, TP Gross, MD, Laboratory of Retrovirology, Div of Transfusion Science, Center for Biologics Evaluation and Research, Food and Drug Administration, Rockville, Maryland.
Agwu reported at the meeting, sponsored by the Foundation for Retrovirology and Human Health and the Centers for Disease Control and Prevention.