Infectious Mononucleosis

Infectious mononucleosis (pronounced MON-o-NOO-klee-O-siss) is a contagious (catching) illness caused by the Epstein-Barr virus (EBV). The virus most commonly infects the liver, lymph nodes, and mouth.


Influenza is a highly infectious disease that affects the respiratory (breathing) tract. It is also known as the flu or grippe.


Insomnia is the inability to get an adequate amount of sleep. The difficulty can be in falling asleep, remaining asleep, or both.

Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a common intestinal condition. Its cause is unknown and there is currently no cure.

Juvenile Arthritis

Juvenile arthritis (JA) refers to a number of different conditions with two characteristics in common. First, they all strike children.

Kaposi's Sarcoma

Kaposi's sarcoma (KS; pronounced kuh-PO-seez sar-KO-muh) is a very rare form of cancer (see cancer entry). The word "sarcom" refers to any form of cancer that affects muscle, bone, liver, kidneys, lungs, spleen, bladder, and other organs and tissues.


Laryngitis (pronounced lar-uhn-JIE-tiss) is an inflammation of the larynx, resulting in hoarseness of the voice.

Lead Poisoning

Lead poisoning occurs when a person swallows lead or breathes in its fumes. The result can be damage to the brain, nerves, and many other parts of the body.

Learning Disorders

Learning disorders are academic problems experienced by children and adults of average to above-average intelligence. Learning disorders involve problems with reading, writing, mathematics, or a combination of these three skills.


Leukemia (pronounced loo-KEE-mee-uh) is a form of cancer (see cancer entry) in which the body produces too many white blood cells. Many forms of leukemia have been identified.


Lice are small, insect-like parasites. Parasites are animals that live off other animals.

Lung Cancer

Lung cancer is a disease in which the cells of lung tissues grow uncontrollably and form tumors. A tumor is a mass or lump of tissue made of abnormal cells.


Lupus is a disease in which a person's immune system attacks the body's own organs and tissues (see autoimmune disorders entry). The complete medical name for lupus is systemic lupus erythematosus (SLE; pronounced LOO-puhs er-uh-THEM-uh-tuhs).

Lyme Disease

Lyme disease is caused by the bacterium Borrelia burgdorferi (Bb). The bacterium is carried by ticks and is transmitted to humans through a tick bite.


Malaria is a serious, infectious disease spread by certain kinds of mosquitoes. It is common in tropical climates and is characterized by chills, fevers, and an enlarged spleen.


Measles is a viral infection (an infection caused by a virus). Its most characteristic feature is a reddish skin rash.


Meningitis (pronounced meh-nen-JI-tiss) is an inflammation of the meninges (pronounced meh-NIN-jeez). The meninges are the thin layers of tissue that cover the brain and the spinal cord.

Mental Retardation

Mental retardation is a developmental disability that is marked by lower-than-normal intelligence and limited daily living skills. Mental retardation is normally present at birth or develops early in life.

Multiple Sclerosis

Multiple sclerosis (MS; pronounced multiple skluh-RO-siss) is a chronic autoimmune disorder (see autoimmune disorders entry) that affects the nerves. "Chronic" means that it develops slowly over time; "autoimmune" means that the body's immune system becomes confused about some part of the body it is designed to protect.


Mumps is a relatively mild viral infection of the salivary glands that usually occurs during childhood. Typically, mumps is characterized by a painful swelling of both cheeks.

Muscular Dystrophy

Muscular dystrophy (MD) is the name for a group of disorders in which muscle size and strength gradually decrease over time. Nine different forms of the disorder have been discovered.


Obesity is an abnormal accumulation of body fat, usually 20 percent or more over an individual's ideal body weight. Obesity is associated with an increased risk of illness, disability, and death.

Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) is a type of anxiety disorder. A person with an anxiety disorder worries excessively about the circumstances of his or her life over a long period of time.


The word "osteoporosis" literally means "porous bones." Osteoporosis (pronounced OSS-tee-o-puh-RO-sis) occurs when bones begin to lose some of their essential elements. The most important of these elements is calcium.

Panic Disorder

Panic disorder is a condition in which a person feels sudden over-whelming fright, usually without any reasonable cause. A panic attack is generally accompanied by physical symptoms, such as a pounding heart, sweating, and rapid breathing.

Parkinson's Disease

Parkinson's disease (PD) is a chronic, progressive disorder of the nervous system. A chronic disorder continues for long periods of time, usually many years.

Periodontal Disease

Periodontal disease affects the tissues that support and anchor the teeth. Left untreated, periodontal disease results in destruction of the gums, parts of the jawbone, and portions of the tooth root.


Pneumonia (pronounced noo-MOAN-ya) is an infection of the lung. It can be caused by a great many different agents, including bacteria, viruses, fungi, and parasites.


Pneumothorax (pronounced noo-moh-thor-ax) is a condition in which air or some other gas collects in the chest or the pleural space. The pleural space is the space that surrounds the lungs.


Polio (pronounced POH-lee-oh) is a serious disease caused by a virus called the poliovirus. The full medical name for the disease is poliomyelitis (pronounced POH-lee-oh-mi-uh-LI-tis).

Posttraumatic Stress Disorder

Posttraumatic stress disorder (PTSD) is a condition that affects people who have gone through a major traumatic (shocking) event. PTSD is characterized by repeated thoughts about the ordeal, a dulling of emotions, an increased tendency to become excited and aroused, and, sometimes, dramatic personality changes.

Prostate Cancer

Prostate cancer is a disease in which the cells of the prostate become abnormal. They start to grow uncontrollably, forming tumors.

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