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Glossary: HIV/AIDS terms and definitions, part 5

transcription: The fourth of seven steps in the HIV life cycle. Transcription occurs after HIV has integrated its viral DNA into the DNA of the host cell. During transcription, the host cell uses the genetic instructions carried in HIV DNA to make new HIV RNA, including HIV messenger RNA (mRNA).

translation: The fifth of seven steps in the HIV life cycle. Translation occurs after the host cell makes new HIV RNA. During translation, the host cell uses the genetic instructions carried in the new HIV RNA, specifically messenger RNA (mRNA), to make HIV proteins.

transmitted resistance: Also known as: Primary Resistance. When a person becomes infected with a strain of HIV that is already resistant to certain antiretroviral (ARV) drugs.

transplacental: Passage through or across the placenta. Transplacental usually refers to the exchange of nutrients, waste products, drugs, infectious organisms, or other substances between the mother and the fetus.

treatment failure: When an antiretroviral (ARV) regimen is unable to control HIV infection. Treatment failure can be clinical failure, immunologic failure, virologic failure, or any combination of the three. Factors that can contribute to treatment failure include drug resistance, drug toxicity, or poor treatment adherence.

treatment regimen: Also known as: Regimen. A structured treatment plan designed to improve and maintain health. Recommended HIV treatment regimens include a combination of three or more antiretroviral (ARV) drugs from at least two different drug classes.

treatment-experienced: When a person with HIV is currently taking or has previously taken antiretroviral (ARV) drugs.

treatment-naïve: When a person with HIV has never taken antiretroviral (ARV) drugs.

triglycerides: A type of fat in blood and adipose (fat) tissue.

triple-class experienced: When an HIV-infected person has received antiretroviral (ARV) drugs from three drug classes — the nucleoside reverse transcriptase inhibitor (NRTI), non-nucleoside reverse transcriptase inhibitor (NNRTI), and protease inhibitor (PI) drug classes.

true negative: A negative test result that correctly indicates that the condition being tested for is not present. For example, a true negative HIV test correctly indicates that a person is not infected with HIV.

true positive: A positive test result that correctly indicates that the condition being tested for is present. For example, a true positive HIV test correctly indicates that a person is infected with HIV.

tuberculosis (TB): An infection caused by the bacteria Mycobacterium tuberculosis and Mycobacterium bovis. Tuberculosis (TB), also referred to as Mycobacterium infection, is spread when a person with an active infection (TB disease) coughs, sneezes, speaks, or sings, and then a person nearby breathes in the bacteria. TB usually affects the lungs, but it can also affect other parts of the body, such as the kidneys, spine, and brain. There are two forms of TB: latent TB infection and TB disease. In people with HIV, TB is considered an AIDS-defining condition.

tuberculosis disease: The active form of tuberculosis (TB) infection. During TB disease, the bacteria multiply, become active, and make the person sick. A person with TB disease of the lungs can spread TB to others. TB disease primarily affects the lungs, but it can also affect other parts of the body, such as the kidneys, spine, and brain, and it can be fatal. Symptoms include a bad cough that lasts three weeks or longer, chest pain, coughing up blood or sputum, weakness, fatigue, loss of appetite, weight loss, fever, chills, and sweating at night. In people with HIV, TB disease is an AIDS defining condition.

tuberculosis skin test: Also known as: purified protein derivative test, tuberculin skin test. A screening test for tuberculosis (TB). Purified protein derivative (PPD) extracted from the bacterium that causes tuberculosis is injected just below the skin (intradermally). After 48 to 72 hours, a health care professional checks the site of injection for a reaction that indicates that the person has been exposed to TB. Following a positive TB skin test, additional tests are necessary to determine whether a person actually has active TB (TB disease). Certain populations, such as children, the elderly, or people with weakened immune systems, may have smaller, delayed, or negative reactions to the TB test even if they are infected with TB.

undetectable viral load: When the amount of HIV in the blood is too low to be detected with a viral load (HIV RNA) test. Antiretroviral (ARV) drugs may reduce a person’s viral load to an undetectable level; however, that does not mean the person is cured. Some HIV, in the form of latent HIV reservoirs, remain inside cells and in body tissues.

urinalysis: Physical, chemical, and microscopic examination of urine. Urinalysis can detect a specific substance, such as glucose or blood, in the urine — this can be helpful in diagnosing a disease or monitoring the body’s response to treatment.

urolithiasis: Calculi (stones) in the urinary tract. Use of some antiretroviral (ARV) drugs may cause urolithiasis.

urticarial: Also known as: hives. Raised, swollen, itchy areas on the skin or mucous membranes, usually caused by an allergic reaction to a drug or food.

vaccination: Also known as: immunization. Giving a vaccine to stimulate a person’s immune response. Vaccination can be intended either to prevent a disease (a preventive vaccine) or to treat a disease (a therapeutic vaccine).

vaccine: Also known as: Inoculation. A substance administered to trigger an immune response against a particular disease. Most vaccines are designed to prevent a person from ever having a particular disease or to only have a mild case of the disease. However, therapeutic vaccines are intended to treat specific diseases. Although researchers are testing vaccines both to prevent and treat HIV/AIDS, no HIV vaccine is currently approved for use outside of clinical trials.

vaccinia: The pox-type virus used in the vaccine that eradicated smallpox. Researchers are studying the possibility of using a modified, milder version of the vaccinia virus to develop a vaccine against HIV infection.

vacuolar myelopathy: A neurological disorder associated with advanced HIV infection. Vacuolar myelopathy causes the protective myelin sheath to pull away from nerve cells of the spinal cord, forming small holes (vacuoles) in nerve fibers. Symptoms of vacuolar myelopathy include weak and stiff legs and unsteadiness when walking.

varicella zoster virus (VZV): Also known as: herpes zoster, human herpesvirus 3. A type of herpesvirus that causes chicken pox. After initial infection with varicella zoster virus (VZV), the inactive (latent) form of the virus can remain in the body. If the latent virus becomes active again, it can cause shingles. vector: In genetically engineered vaccines, a vector is a bacterium or virus that transports antigen-coding genes into the body to provoke an immune response. (The vector itself does not provoke an immune response or cause disease.) A vector may also refer to an organism, especially an insect, that transmits disease-causing agents.

vertical transmission: Vertical transmission of HIV refers to HIV transmission from an HIV-infected mother to her child during pregnancy, labor and delivery, or breastfeeding (through breast milk).

viral evolution: The change in the genetic makeup of a virus population as the viruses mutate and multiply over time. HIV evolves rapidly because of its high mutation and replication rates. Antiretroviral therapy (ART) and the body’s immune response can also influence HIV evolution.

viral latency: When a virus is present in the body but exists in a resting (latent) state without producing more virus. A latent viral infection usually does not cause any noticeable symptoms and can last a long period of time before becoming active and causing symptoms. HIV is capable of viral latency, as seen in the reservoirs of latent HIV-infected cells that persist in a person’s body despite antiretroviral therapy (ART).

viral load (VL): The amount of HIV in a sample of blood. Viral load (VL) is reported as the number of HIV RNA copies per milliliter of blood. An important goal of antiretroviral therapy (ART) is to suppress a person’s VL to an undetectable level—a level too low for the virus to be detected by a VL test.

viral load test: A laboratory test that measures the amount of HIV in a blood CERTIFICATION sample. Results are reported as the number of copies of HIV RNA per milliliter of blood. Examples of viral load tests include quantitative branched DNA (bDNA), reverse transcriptase-polymerase chain reaction (RT-PCR), and qualitative transcription-mediated amplification. Viral load tests are used to diagnose acute HIV infection, guide treatment choices, and monitor response to antiretroviral therapy (ART).

viral rebound: Also known as: rebound. When a person on antiretroviral therapy (ART) has persistent, detectable levels of HIV in the blood after a period of undetectable levels. Causes of viral rebound can include drug resistance or poor adherence to an HIV treatment regimen.

viral replication: Also known as: replication. The process by which a virus multiplies.

viral suppression: Also known as: virologic control. When antiretroviral therapy (ART) reduces a person’s viral load (HIV RNA) to an undetectable level. Viral suppression does not mean a person is cured; HIV still remains in the body. If ART is discontinued, the person’s viral load will likely return to a detectable level.

viral tropism: Also known as: tropism. When HIV selectively attaches to a particular coreceptor on the surface of the host cell. HIV can attach to either the CCR5 coreceptor (R5-tropic) or the CXCR4 coreceptor (X4-tropic) or both (dual-tropic).

viremia: The presence of viruses in the blood.

viricide: Also known as: virucide. A substance that can destroy or inactivate a virus.

virologic failure: A type of HIV treatment failure. Virologic failure occurs when antiretroviral therapy (ART) fails to suppress and sustain a person’s viral load to less than 200 copies/mL. Factors that can contribute to virologic failure include drug resistance, drug toxicity, and poor treatment adherence.

virology: The study of viruses and viral diseases.

virus: A microscopic infectious agent that requires a living host cell in order to replicate. Viruses often cause disease in humans, including measles, mumps, rubella, polio, influenza, and the common cold. HIV is the virus that causes AIDS.

visceral adipose tissue (VAT): Also known as: intra-abdominal fat, visceral fat. Fat tissue located deep in the abdomen and around internal organs. Use of certain antiretroviral (ARV) drugs can cause excessive accumulation of visceral adipose tissue (VAT), which increases the risk of heart attack, stroke, and diabetes.

wasting syndrome: An involuntary loss of more than 10% of body weight (especially muscle mass), plus at least 30 days of either diarrhea or weakness and fever. HIV-associated wasting syndrome is an AIDS-defining condition.

Western blot: A type of antibody test used to confirm a positive result on an HIV screening test. (The initial screening test is usually an enzyme-linked immunosorbent assay [ELISA] or, less often, a viral load test). The immune system responds to HIV infection by producing HIV antibodies. A Western blot can detect HIV antibodies in the blood, oral fluid, or urine.

white blood cell: Also known as: leukocyte. A type of cell found in blood and lymph. White blood cells are key components of the immune system and help fight infection and disease. Examples of white blood cells include lymphocytes, neutrophils, eosinophils, macrophages, and mast cells.

wild-type virus: The naturally occurring, non-mutated strain of a virus. When exposed to antiretroviral (ARV) drugs, wild-type HIV can develop mutations that make the virus resistant to specific ARV drugs.

window period: The time period from infection with HIV until the body produces enough HIV antibodies to be detected by an HIV antibody test. This generally takes two to eight weeks, but in some people it can take up to six months. During the window period, a person can have a negative result on an HIV antibody test despite being infected with HIV.

Women’s Interagency HIV Study (WIHS): Started in 1993, the Women’s Interagency HIV Study (WIHS) is an ongoing federally funded study on women who have HIV or who are at risk for HIV. Analysis of biological specimens and medical and behavioral data collected on WIHS participants has contributed to the understanding of HIV, AIDS, and the effects of antiretroviral therapy (ART) in women.

World Health Organization (WHO): The agency of the United Nations that provides global leadership on health-related matters. Responsibilities of the World Health Organization (WHO) include shaping the global health research agenda, setting health standards, promoting evidence-based policy options, providing technical support to countries, and monitoring and assessing health trends.

X4-Tropic Virus: Also known as: T-tropic virus. A strain of HIV that enters and infects a host cell by binding to the CXCR4 receptor on the host cell. To enter a host cell, HIV must first attach to a CD4 receptor, then attach to either the CCR5 or CXCR4 receptor, and finally fuse its membrane with the host cell membrane. HIV is usually R5-tropic (uses CCR5) during the early stages of infection, but the virus may later switch to using either CXCR4 or both CCR5 and CXCR4.

This glossary of HIV/AIDS-related terms is from the U.S. Government Source for HIV/AIDS Medical Practice Guidelines, Clinical Trials, and Other Research Information. It was found online at the National Institutes of Health website,