HAART
See: Highly Active Antiretroviral Therapy

Half-Life
The time period in which the concentration of a drug falls to half its original concentration.

HBV
See: Hepatitis B Virus

HCFA
See: Health Care Financing Administration

HCV
See: Hepatitis C Virus

Health Care Financing Administration (HCFA)
See:    Centers for Medicare and Medicaid Services

Health Resources and Services Administration (HRSA)
A U.S. Department of Health and Human Services (DHHS) agency that directs national health programs aimed at improving the health of Americans by assuring quality health care to underserved, vulnerable, and special-needs populations. Among other functions, HRSA administers the Ryan White Comprehensive AIDS Resources Emergency (CARE) Act and the AIDS Education and Training Centers (AETCs) to provide treatment and services for those affected by HIV/AIDS.
See Also:   AIDS Education and Training Centers
                   Ryan White Care Act

HELLP Syndrome
A term that stands for Hemolysis, Elevated Liver enzyme levels, and a Low Platelet count. This is a rare but serious complication that can develop in the third trimester of pregnancy. Symptoms may include liver, blood pressure, and bleeding problems that can harm both the mother and the baby. Pregnant women taking NRTIs for HIV infection are at an increased risk for developing HELLP syndrome.

Helper T Cells
See:    CD4 Cell

Hematocrit
A laboratory measurement that determines the percentage of red blood cells in a sample of blood. In women, red blood cells are normally 37 to 47 percent of the blood. In men, red blood cells are normally 40 to 54 percent of the blood.

Hematotoxic
Toxic or destructive to the blood or bone marrow.

Hemoglobin
A protein in red blood cells that transports oxygen from the lungs to the tissues of the body.

Hemolysis
Rupture of red blood cell membranes, causing a release of hemoglobin.
See Also:   Hemoglobin

Hemophilia
A hereditary blood defect that occurs almost exclusively in males and is characterized by delayed clotting of the blood. This leads to difficulty in controlling bleeding, even after minor injuries.

Hepatic
Pertaining to the liver.

Hepatic Necrosis
Death of liver cells.
See Also:   Hepatotoxicity

Hepatic Steatosis
Accumulation of too much fat inside liver cells. Also known as "fatty liver."
See Also:   Lactic Acidosis

Hepatitis
Inflammation of the liver. This condition can lead to liver damage and liver cancer.
See Also:   Hepatitis B Virus
                   Hepatitis C Virus

Hepatitis B Virus (HBV)
The virus that causes hepatitis B, an inflammation of the liver that can lead to liver damage and liver cancer. HBV is spread through contact with the blood of an infected person, through sexual intercourse, or from mother to child during childbirth. A vaccine is available to prevent infection with this virus, and hepatitis B can be treated with several drugs.

Hepatitis C Virus (HCV)
The virus that causes hepatitis C, an inflammation of the liver that can lead to liver damage and liver cancer. HCV is primarily spread through contact with the blood of an infected person. There is no vaccine for HCV, and the only current treatment for hepatitis C is a combination of the drugs peginterferon and ribavirin.

Hepatomegaly
Enlargement of the liver.

Hepatotoxicity
A general term for liver damage. Often caused by medications, including those used to treat HIV infection. Symptoms of hepatotoxicity include nausea, vomiting, abdominal pain, loss of appetite, diarrhea, unusual tiredness or weakness, jaundice (yellowing of the skin and eyes), and unusual swelling or weight gain. Laboratory testing may show increased levels of liver enzymes in the blood.
See Also:   Liver Function Tests

Herpes Simplex Virus 1 (HSV-1)
A virus that causes cold sores or fever blisters on the mouth or around the eyes, and can be transmitted to the genital region. The virus can become latent (inactive) and symptoms disappear. Stress, trauma, other infections, or suppression of the immune system can reactivate the latent virus and symptoms can return.
See Also:   Herpesviruses

Herpes Simplex Virus 2 (HSV-2)
A virus that causes painful sores around the anus or genitals. The virus can become latent (inactive) and symptoms then disappear until the virus is reactivated. HSV-2 may be transmitted either sexually or from an infected mother to her infant during birth.

Herpes Zoster
See:    Varicella Zoster Virus

Herpesviruses
A family of viruses containing several individual members, including herpes simplex viruses 1 and 2 (HSV-1 and -2), cytomegalovirus (CMV), varicella zoster virus (VZV), Epstein-Barr virus (EBV), and Kaposi's sarcoma herpesvirus (KSHV or HHV-8). Each of these viruses can cause disease in humans.

HGH
See: Human Growth Hormone

Highly Active Antiretroviral Therapy (HAART)
The name given to treatment regimens that aggressively suppress HIV replication and progression of HIV disease. The usual HAART regimen combines three or more anti-HIV drugs.

Histoplasmosis
A lung disease caused by the fungus Histoplasma capsulatum. Symptoms are similar to those of influenza. People with severely damaged immune systems, such as those with AIDS, are vulnerable to a very serious form of the disease called progressive disseminated histoplasmosis. This form of histoplasmosis typically lasts a long time and involves other organs besides the lungs. Histoplasmosis is considered an AIDS-defining condition in people with HIV.

HIV
See: Human Immunodeficiency Virus

HIV Prevention Trials Network (HPTN)
A worldwide clinical trials network established by the National Institutes of Health (NIH) to develop and evaluate the safety and efficacy of non-vaccine HIV prevention methods designed to prevent the transmission of HIV.

HIV Vaccine Trials Network (HVTN)
An international group of scientists and educators that was formed in 1999 by the Division of AIDS of the National Institute of Allergy and Infectious Diseases (NIAID). The main goal of HVTN is to find a safe and effective preventive HIV vaccine. HVTN staff and volunteers around the world are also involved in helping community members understand the general science of HIV/AIDS vaccines, as well as research methods and clinical trials processes.
See Also:   Preventive HIV Vaccine

HIV-1
The HIV type responsible for the majority of HIV infections worldwide.
See Also:   Human Immunodeficiency Virus
                   HIV-2

HIV-2
A virus closely related to HIV-1 that also causes immune suppression and AIDS. Although the two viruses are very similar, immunodeficiency seems to develop more slowly and to be milder in people infected with HIV-2. The majority of HIV-2 cases have been found in West Africa. Not all drugs used to treat HIV-1 infection are effective against HIV-2.
See Also:   Human Immunodeficiency Virus
                   HIV-1

Hodgkin's Lymphoma
A type of cancer that affects certain white blood cells. Symptoms include enlarged lymph nodes, fever, night sweats, weight loss, and itching. This type of cancer most commonly affects people ages 15 to 40, people over 55, and people who are HIV infected. It is also known as Hodgkin's disease.
See Also:   Lymphoma
                   Non-Hodgkin's Lymphoma

Horizontal Transmission
A term used to describe transmission of a disease from one individual to another, except from parent to offspring. For example, HIV can be spread horizontally through sexual contact or exposure to infected blood. In contrast, spread of disease from parent to offspring is called vertical transmission.
See Also:   Vertical Transmission

Hormone
A chemical produced in one part of the body and passed through the blood to another part of the body to regulate its structure or function. HIV infection and AIDS can affect the production of hormones, causing imbalances in such hormones as estrogen and testosterone.

HPTN
See: HIV Prevention Trials Network

HPV
See: Human Papillomavirus

HRSA
See: Health Resources and Services Administration

HSV-1
See: Herpes Simplex Virus 1

HSV-2
See: Herpes Simplex Virus 2

HTLV-I
See: Human T-Cell Lymphotropic Virus Type I

Human Growth Hormone (HGH)
A protein produced in the pituitary gland that stimulates the liver to produce somatomedins, substances that stimulate growth of bone and muscle. A laboratory-made version of HGH, called serostim, has been approved by the Food and Drug Administration (FDA) as a treatment for AIDS wasting syndrome.
See Also:   Wasting Syndrome

Human Herpesviruses
See:    Herpesviruses

Human Immunodeficiency Virus (HIV)
The virus that causes Acquired Immunodeficiency Syndrome (AIDS). HIV is in the retrovirus family, and two types have been identified: HIV-1 and HIV-2. HIV-1 is responsible for most HIV infections throughout the world, while HIV-2 is found primarily in West Africa.
See Also:   Acquired Immunodeficiency Syndrome
                   Retrovirus

Human Leukocyte Antigen
Also known as major histocompatibility complex (MHC). Proteins found on the outside of almost every cell in the body that play an important role in controlling the immune system. The type of HLA proteins a person inherits from his or her parents is important in identifying good "matches" for tissue grafts and organ transplants. Some HLA types are also associated with either a faster or slower progression of HIV disease.

Human Papillomavirus (HPV)
Viruses that cause various warts, including plantar and genital warts. Some strains of HPV can also cause cervical cancer.
See Also:   Cervical Cancer
                   Genital Warts

Human T-Cell Lymphotropic Virus Type I (HTLV-I)
A virus in the same family (retrovirus) as HIV. In rare cases, HTLV-1 can cause adult T-cell leukemia/lymphoma, a rare and aggressive cancer of the blood. People infected with HTLV-1 may also develop myelopathy, a disease of the spinal cord.
See Also:   Retrovirus

Humoral Immunity
Term used to describe the body's antibody-based immune response, as opposed to its cell-based immune response (cellular immunity). Immune cells called B cells produce antibodies against foreign invaders.
See Also:   Antibody
                   Cell-Mediated Immunity
                   B Lymphocytes

HVTN
See: HIV Vaccine Trials Network

Hyperadiposity
See:    Lipohypertrophy

Hypergammaglobulinemia
Higher than normal amounts of gamma globulins (antibodies) in the blood.
See Also:   Antibody

Hyperglycemia
Higher than normal glucose (sugar) levels in the blood.
See Also:   Diabetes

Hyperlipidemia
Elevated concentration of lipids (cholesterol, triglycerides, or both) in the blood. Hyperlipidemia increases the risk of serious heart diseases. In HIV-infected inidividuals, hyperlipidemia may occur as a side effect of PI treatment.

Hyperplasia
An abnormal increase in the number of cells in a tissue or an organ.

Hypogammaglobulinemia
A deficiency of gamma globulins (antibodies) in the blood. This condition may occur in late stages of HIV disease when the immune system has been severely damaged.
See Also:   Antibody

Hypogonadism
Inadequate activity of the ovaries or testes. This can result in abnormally low levels of gonadal hormones (androgens and estrogens) and problems with sperm or egg production. Hypogonadism may occur in men and women with HIV disease.

Hypoxia
A condition in which not enough oxygen reaches the tissues of the body.