Kids Research Express

Alzheimer’s Disease, progressive brain disorder that causes a gradual and irreversible decline in memory , language skills, perception of time and space, and, eventually, the ability to care for oneself. First described by German psychiatrist Alois Alzheimer in 1906, Alzheimer’s disease was initially thought to be a rare condition affecting only young people, and was referred to as presenile dementia. Although Alzheimer’s disease is not a normal part of the aging process, the risk of developing the disease increases as people grow older. About 10 percent of the United States population over the age of 65 is affected by Alzheimer’s disease, and nearly 50 percent of those over age 85 may have the disease. Alzheimer’s disease takes a devastating toll, not only on the patients, but also on those who love and care for them. Some patients experience immense fear and frustration as they struggle with once commonplace tasks and slowly lose their independence. Family, friends, and especially th...

Common Cold, acute infectious disease of the upper respiratory tract, caused by more than 100 kinds of viruses. The infection affects the mucous membranes of the nose and throat, causing such symptoms as nasal congestion and discharge, sore throat, and coughing. These symptoms are typical also of respiratory infections caused by bacteria, and of allergic conditions such as hay fever and asthma ; therefore, the common cold is difficult to diagnose with certainty. Normally it runs a mild course, without fever, and subsides spontaneously in about seven days. Its medical significance lies in the possible complications that may ensue. Various diseases, such as bronchitis, pneumonia, and sinus or middle-ear infections, may arise from the cold. Research indicates that there are several strains of each type of virus with varying degrees of virulence. Infection with one strain confers only a brief immunity to reinfection by the same strain, and gives no immunity against the other strains. In 1...

Gout, complex disease of uncertain origin caused by the faulty metabolism of uric acid produced in the body by breakdown of protein, and resulting in elevated levels of uric acid in the blood. A diet rich in malt liquors, wines, and certain types of protein may precipitate individual attacks but does not cause the disease. Its incidence is not usually affected by climate or season; about 95 percent of sufferers are men. The disease is rare in people under the age of 30; from 10 to 20 percent of cases have a familial history. Acute attacks are characterized by severe pain in the joints, often in the big toe, but sometimes in the ankle, knee, hip, shoulder, wrist, or elbow. The attack usually begins abruptly; the joint becomes swollen, red, inflamed, and extremely tender. Untreated attacks last from a few days to a week or more. Repeated attacks may result in the development of a condition known as chronic tophaceous gout. In this condition crystals of uric acid lodge as white, chalky ma...

Human Immunodeficiency Virus, infectious agent that causes acquired immunodeficiency syndrome (AIDS), a disease that leaves a person vulnerable to life-threatening infections. Scientists have identified two types of this virus. HIV-1 is the primary cause of AIDS worldwide. HIV-2 is found mostly in West Africa. HIV belongs to the retrovirus family of viruses, whose members share a unique method of replicating themselves when they infect living cells. Retroviruses store their genetic information in molecules of ribonucleic acid (RNA). However, unlike other RNA viruses, retroviruses use RNA as a template (master pattern) for forming deoxyribonucleic acid (DNA), the genetic material that puts viral replication instructions into effect. This process, called reverse transcription, is the exact opposite of the normal flow of genetic information in living things, in which DNA serves as the template for RNA formation (see Genetics ). HIV consists of a flexible outer membrane, called the enve...

Parkinson Disease, disorder of the nervous system that affects muscle control. Marked by trembling of the arms and legs, muscular rigidity, and poor balance, Parkinson disease is slowly progressive, worsening over time. Eventually symptoms may cause problems with walking or talking and, in some people, difficulty thinking. Physicians do not know how to cure Parkinson disease, but drug therapy or surgery may alleviate some of the most troubling symptoms. The disease is named for British physician James Parkinson, who first described it in 1817. In a report describing six patients, Parkinson called the disorder paralysis agitans, Latin words that mean “shaking palsy.” Parkinson disease develops as a part of the brain known as the substantia nigra degenerates. The substantia nigra is located in the midbrain, halfway between the cerebral cortex and the spinal cord. In healthy people, the substantia nigra contains certain nerve cells, called nigral cells, that produce the chemical dopamine...

Allergy, exaggerated and sometimes harmful reactions to external substances, called allergens . Allergy may result from exposure to such common allergens as plant pollens from grasses, trees, or ragweed; animal danders, which are tiny scales shed from the skin and hair of cats and other furred animals; arachnids and insects, such as house dust mites, bees, and wasps; and drugs, such as penicillin. The most common food allergies are caused by eggs, milk, peanuts, shellfish, wheat, and chocolate. Diagnosing and treating allergies is usually performed by an allergist, a physician trained to understand the body's immune response. When visiting an allergist for the first time, a patient is usually asked which substances seem to provoke symptoms and whether other family members have allergies. The doctor conducts a brief physical examination, looking in the nose, eyes, ears, and throat, listening to the chest, and examining the skin. For most patients with allergies, medicines are used t...

Acquired Immunodeficiency Syndrome (AIDS), human viral disease that ravages the immune system, undermining the body’s ability to defend itself from infection and disease. Caused by the human immunodeficiency virus (HIV), AIDS leaves an infected person vulnerable to opportunistic infections. Such infections are harmless in healthy people, but in those whose immune systems have been greatly weakened, they can prove fatal. Although there is no cure for AIDS, new drugs are available that can prolong the life spans and improve the quality of life of infected people. Infection with HIV does not necessarily mean that a person has AIDS. Some people who have HIV infection may not develop any of the clinical illnesses that define the full-blown disease of AIDS for ten years or more. Physicians prefer to use the term AIDS for cases where a person has reached the final, life-threatening stage of HIV infection.

Acne, eruptive skin disease. It is primarily a disorder of the sebaceous follicles of the skin and appears most often on the face, neck, and back. The natural secretion, or sebum, of the follicles accumulates and mixes with dust and dirt. The follicles and surrounding tissue become inflamed and blackheads appear. If the follicle opening completely closes, the accumulated sebum is degraded by bacteria and forms a cyst. Acne vulgaris, the most common form, is usually associated with adolescence but may also occur in adults. A severe form of the disorder is known as acne conglobata. Other forms of acne are also observed, such as the chloracne caused by chlorinated compounds. In acne rosacea, the capillaries in the cheeks, forehead, and nose are swollen with blood and the oil glands in the skin become infected. Acne in adolescence results primarily from hormonal changes taking place in the body; the hormones stimulate sebum production. Outbreaks cannot be prevented by a controlled diet and...

Lyme Disease, bacterial disease transmitted to people by ticks . Lyme disease is caused by a spiral-shaped bacterium known as Borrelia burgdorferi. This bacterium is frequently carried by ticks of the genus Ixodes, primarily the deer tick (also known as the black-legged tick) and the related Western black-legged tick. Immature ticks become infected by feeding on small rodents, such as the white-footed mouse, and other mammals that are infected with the bacteria. Early symptoms of Lyme disease include a red, circular, smooth rash that expands in size and may resemble a bull's-eye. The rash is painless, does not itch, and may disappear on its own. Several days to several weeks after infection, an infected person may develop flulike symptoms such as fever, headache, a stiff neck, joint and muscle pain, and severe fatigue. Doctors often treat patients early in the disease solely on the basis of their symptoms and if they have had a known or likely exposure to infected ticks. In the lat...

Mumps, acute infectious disease caused by a virus that mainly attacks glandular and nervous tissues, frequently characterized by swelling of the salivary glands . The disease is worldwide in distribution and can occur in epidemics. Its incidence is highest between the ages of 5 and 9, but mumps may attack persons of any age. Because the salivary gland most often affected is the parotid, mumps is also known as epidemic parotitis. The disease rarely involves the sex glands, the meninges, or the pancreas. Mumps is spread from person to person by droplets sprayed from the respiratory tract of infected persons, and it is highly contagious. The incubation period of the disease varies from 15 to 21 days. Few fatalities result from mumps, and one attack usually confers complete immunity, because only one antigenic type of virus causes this disease. In children, the first symptoms are usually a mild fever, a feeling of illness and chilliness, loss of appetite, and dryness of the throat. This is...

Rabies, acute, contagious infection of the central nervous system, caused by a specific virus that enters the body through the bite of an animal. All warm-blooded animals are susceptible, but in North America the disease is most common in skunks, foxes, bats, raccoons, dogs, and cats. Most of the cases of rabies in humans are caused by the bite of one of these animals. The incubation period in humans varies from three weeks to 120 days, with an average of about four to six weeks. Rabies is virtually always fatal when vaccine is not administered. Modern treatment, following a bite by a rabid or presumed rabid animal, consists of immediate and thorough cleansing of the bite wound and injection into the wound and elsewhere of hyperimmune antirabies serum. A 14- to 30-day course of daily injections of rabies vaccine is then given; booster doses are given 10 days after this course and again 20 days later.

Addison’s Disease, chronic endocrine disorder resulting from underactive adrenal glands that do not produce enough corticosteroid hormones. The disease was first described by the British physician Thomas Addison in 1855. Adrenal glands may be adversely affected by a severe infection , such as tuberculosis , massive bleeding of the adrenals, or surgery affecting the glands, such as removal of a tumor , but in most cases the origin of the disease is unknown. The resulting lack of hormone secretion causes such symptoms as weakness and fatigue, weight loss, low blood pressure , gastrointestinal distress, low blood sugar, depression and irritability, and increased skin pigmentation.

Viruses are responsible for many common human diseases, such as colds, flu, diarrhea, chicken pox , measles , and mumps. Some viral diseases—such as rabies , hemorrhagic fevers, encephalitis, polio, yellow fever, and acquired immunodeficiency syndrome (AIDS)—can result in death. German measles and cytomegalovirus can cause serious abnormalities or death in unborn infants.

Mononucleosis, Infectious, also glandular fever, an acute disease of humans, caused by the Epstein-Barr virus. Its mode of transmission is not known, but may be facilitated by saliva exchange, as in kissing. The disease , which attacks chiefly adolescents and young adults, usually runs its course in two to four weeks, although cases may be as brief as a week or last six to eight weeks. After recovery, weakness may continue for several months. Mononucleosis is characterized by fever, sore throat, fatigue, malaise, and loss of appetite, often associated with nausea. Patients generally have swelling of the lymph nodes in the neck and elsewhere and often have an enlarged spleen. Examination of the blood usually shows an increase in the white blood cells, due to the appearance in the blood of many atypical lymphocytes. The blood serum in infectious mononucleosis often contains an antibody known as heterophile antibody that agglutinates, or clumps, the red blood cells of sheep. Serological t...

Pneumonia, inflammation of one or both lungs . In people with pneumonia, air sacs in the lungs fill with fluid, preventing oxygen from reaching blood cells and nourishing the other cells of the body. Sometimes the inflammation occurs in scattered patches in the tissue around the ends of the bronchioles, the smallest air tubes in the lungs. This is known as bronchopneumonia. In other cases the inflammation is widespread and involves an entire lobe of the lung. This condition is called lobar pneumonia. In the United States about 5 million cases of pneumonia are reported each year and about 63,500 people die from the disease. Most cases of pneumonia result from infection with microorganisms, primarily viruses , bacteria , mycoplasmas (small, free-living particles with characteristics of both bacteria and viruses), and fungi . Pneumonia may also result from certain kinds of allergic reactions, inhalation of fluids or some gases, and the inhalation of ingested foods. To determine the cause ...

Endocarditis, infection and inflammation of the membrane lining the inner surface of the heart, including the heart valves. The two major forms of the disease are the acute type, which appears suddenly and can be fatal within a few days, and the subacute type, which develops slowly and may cause death within months. Many cases of the acute form are caused by the bacterium Staphylococcus aureus ; the subacute form is often due to infection by streptococcal bacteria. Either type can result from fungus infections . Subacute bacterial endocarditis usually results in fever, toxemia , and lesions of the heart valves; particles dislodged from these lesions often cause embolism . Infection of the heart valves and lining, or endocardium, may come from primary infections of the teeth, tonsils, and sinuses. The disease is characterized by the formation of bacterial or fungal growths on the valves and endocardium. It has its greatest incidence in people between the ages of 30 and 50 years. Antib...

Rheumatic Fever, once common acute inflammatory disease, characterized by fever and pain, tenderness, redness, and swelling of the joints. Rheumatic fever can cause inflammation of the heart and damage to the heart valves ( Endocarditis ). First attacks usually occur from the age of 7 to 12 or 14; recurrent attacks can occur throughout adult life. The mortality from the acute attack is low, and most cases subside spontaneously. Often, however, inflammation of the heart leads to scarring and deformity, causing the valves to malfunction. This strain on the heart muscle causes rheumatic heart disease, which can cause death in middle or later life. Acute rheumatic fever is a complication of streptococcal infection, such as strep throat, scarlet fever, or erysipelas. It sometimes develops after infections so mild as to pass unnoticed. Rheumatic fever begins either insidiously or abruptly after a latent period of two to six weeks following the streptococcal infection. Aside from fever, malai...

Tuberculosis (TB), chronic or acute bacterial infection that primarily attacks the lungs, but which may also affect the kidneys, bones, lymph nodes, and brain. The disease is caused by Mycobacterium tuberculosis, a rod-shaped bacterium. Symptoms of TB include coughing, chest pain, shortness of breath, loss of appetite, weight loss, fever, chills, and fatigue. Children and people with weakened immune systems are the most susceptible to TB. Half of all untreated TB cases are fatal. TB is transmitted from person to person, usually by inhaling bacteria-carrying air droplets. When a person sick with TB coughs, sneezes, or speaks, small particles that carry two to three bacteria surrounded by a layer of moisture are released in the air. When another person inhales these particles, the bacteria may lodge in that person’s lungs and multiply. Diagnosis of TB requires two separate methods. Tuberculin skin testing is a method of screening for exposure to TB infection. A person who was infec...