Alzheimer’s Disease

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 those who provide daily care suffer immeasurable pain and stress as they witness Alzheimer’s disease slowly take their loved one from them.

The causes of Alzheimer’s disease remain a mystery, but researchers have found that particular groups of people have risk factors that make them more likely to develop the disease than the general population. For example, people with a family history of Alzheimer’s are more likely to develop Alzheimer’s disease.

DIAGNOSIS

Alzheimer’s disease is only positively diagnosed by examining brain tissue under a microscope to see the hallmark plaques and tangles, and this is only possible after a patient dies. As a result, physicians rely on a series of other techniques to diagnose probable Alzheimer’s disease in living patients. Diagnosis begins by ruling out other problems that cause memory loss, such as stroke, depression, alcoholism, and the use of certain prescription drugs. The patient undergoes a thorough examination, including specialized brain scans, to eliminate other disorders. The patient may be given a detailed evaluation called a neuropsychological examination, which is designed to evaluate a patient’s ability to perform specific mental tasks. This helps the physician determine whether the patient is showing the characteristic symptoms of Alzheimer’s disease—progressively worsening memory problems, language difficulties, and trouble with spatial direction and time. The physician also asks about the patient’s family medical history to learn about any past serious illnesses, which may give a hint about the patient’s current symptoms.

TREATMENT

There is no known cure for Alzheimer’s disease, and treatment focuses on lessening symptoms and attempting to slow the course of the disease. Drugs that increase or improve the function of brain acetylcholine, the neurotransmitter that affects memory, have been approved by the United States Food and Drug Administration (FDA) for the treatment of Alzheimer’s disease. Called acetylcholinesterase inhibitors, these drugs have had modest but clearly positive effects on the symptoms of the disease. These drugs can benefit patients at all stages of illness, but they are particularly effective in the middle stage. This finding corresponds with new evidence that low acetylcholine levels in patients with Alzheimer’s disease may not be present in the earliest stage of the illness.

Cold, Common

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 1985, United States researchers using advanced X-ray crystallography techniques produced a three-dimensional, atomic scale model of one of the most common cold viruses. Study of the antibody binding sites on the viral coat revealed a very high degree of antigenic variability, suggesting that production of a vaccine to protect people from the common cold may never be practical.

Methods of treating a cold are directed toward the relief of symptoms and the prevention of complications. Bed rest is commonly recommended to avoid complications, even when the cold itself is not incapacitating. Antibiotics are often administered as a preventive measure, but there is no evidence that they are helpful.

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Gout

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 material in soft body tissues and in and about the joints, where they may cause bursitis and destruction of bone. Large and deforming deposits may, after many years, settle in the outer margins of the ears, a characteristic feature of the disease. Chronic gout may also cause kidney damage by the formation of uric acid stones, a condition called urate, or gouty, nephropathy.

The treatment of both types of gout calls for complete rest of the limb and a simple diet, low in poultry, legumes, liver and other organ meats and high water intake to reduce the uric acid content of the body. Sodium salicylate and corticosteroids may be prescribed, or a corticosteriod may be injected into the affected joint. The acute phase is managed with anti-inflammatory drugs, such as colchicine or indomethacin. Chronic gout is usually treated by agents that promote excretion of uric acid, such as probenecid, and agents that inhibit production of uric acid, such as allopurinol.

Human Immunodeficiency Virus

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 envelope, that surrounds a protein case known as the capsid. The envelope is studded with glycoproteins, chemical receptors that enable the virus to lock onto target cells. Inside the capsid reside two identical strands of RNA. These RNA strands make up the virus’s genetic program and store all the instructions needed to replicate HIV once it has infected a host cell. HIV also contains molecules of an enzyme called reverse transcriptase. When HIV infects a cell, reverse transcriptase copies the genetic instructions in the virus’s RNA and uses the instructions to build complementary strands of DNA.

See: How HIV Causes Infections; HIV Treatment

Parkinson Disease

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. Dopamine travels along nerve cell pathways from the substantia nigra to another region of the brain, called the striatum. In the striatum, dopamine activates nerve cells that coordinate normal muscle activity. In people with Parkinson disease, nigral cells deteriorate and die at an accelerated rate, and the loss of these cells reduces the supply of dopamine to the striatum. Without adequate dopamine, nerve cells of the striatum activate improperly, impairing a person’s ability to control movement.

Parkinson disease most notably affects motor control (muscle activity). The disease progresses differently for each individual—symptoms develop swiftly in some people and slowly in others. Some Parkinson patients may develop problems that affect their intellect or ability to reason, or they may suffer from depression or anxiety.

Doctors look for the presence of four principal symptoms in patients they suspect may have Parkinson disease. Tremor (the involuntary shaking of limbs) is the major symptom for most people who have Parkinson disease, although at least a third of people diagnosed with the disease do not develop this symptom. Tremor typically begins in one hand but may eventually progress to the other hand, as well as to the arms, legs, and jaw.

There is no known cure for Parkinson disease—that is, no treatment that prevents the disease from progressing. But the symptoms of the disease can be controlled by various drugs such as Levodopa, and, in some cases, by surgery.

Allergy

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 to begin therapy. Most forms of hay fever are easily managed with antihistamines, which relieve the symptoms, such as itching and sneezing, produced by histamine. Asthma is usually treated with medications taken orally or inhaled in vapor form using a metered-dose inhaler. Asthma medications include bronchodilators (drugs that expand the air passages) and anti-inflammatory steroids, which suppress the immune response that causes airway inflammation. In cases of anaphylactic shock, emergency treatment with an injection of adrenaline, also known as epinephrine, is required. This injection quickly widens blood vessels and opens up constricted airways.

Acquired Immunodeficiency Syndrome

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

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 are not a sign of uncleanliness. Good hygiene should be observed, however, to prevent more serious infections. Severe acne may be treated by antibiotics, benzoyl peroxide, or vitamin A derivatives. Severe acne in adults may be a sign of an underlying

Lyme Disease

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 later stage of disease, blood tests are available that measure the body's antibody response against the Borrelia burgdorferi bacteria. These tests are unreliable if used within four weeks of infection because antibody levels may be too low to be detected. Tests designed to detect the presence of the bacterium itself are under development.

Physicians treat Lyme disease with antibiotics. Most patients in the early stages of Lyme disease respond well after two to four weeks of medication. Patients may have persistent fatigue and achiness after treatment, but these symptoms generally resolve within six months. Patients in a later stage of the disease with more severe symptoms may require treatment with one or more intravenous antibiotics for up to six weeks. People in the later stage of the disease typically respond slowly to antibiotic treatment and some people may continue to suffer from symptoms for years.

Mumps

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 followed by soreness and swelling around the ears, and a higher fever. These symptoms are usually gone by 12 days. In adult males, inflammation of the testes occurs in up to 20 percent of the cases, but resultant sterility is rare. In children, infection of the auditory nerve can cause deafness, but this is also a rare result.

Persons exposed to mumps are usually quarantined. Many persons have mumps in such a mild form, however, that it is not recognized, but they still acquire immunity to the disease.

Rabies

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

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 That Cause Human Disease

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

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 tests based on this property of the patient's serum may serve to confirm the diagnosis of the disease. In addition, tests for liver function frequently show mild abnormalities. No therapeutic agent has proved effective in the treatment of mononucleosis.

See also List of human diseases caused by viruses

Pneumonia

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 of pneumonia, a physician takes a sample of the patient's sputum. Analysis of the sputum in the laboratory may identify the particular kind of microorganism causing the infection. Identification of the cause of pneumonia is important in determining treatment.

Antibiotics can cure bacterial pneumonia and speed recovery from mycoplasma pneumonia and PCP. Antibiotics rarely have an effect on pneumonia caused by viruses. However, patients with viral pneumonia often receive antibiotics to prevent bacterial pneumonia from developing during the course of their illness. In addition to drug treatment, a patient with pneumonia should stay in bed, eat healthy meals, and drink large amounts of liquids. Medication may be given to relieve chest pain and violent coughing, and oxygen may be administered if the patient has difficulty breathing. A vaccine is available that confers immunity against pneumococcus. The vaccine is given to people most at risk for developing pneumonia—those over the age of 65 and those with chronic heart, lung, or liver disease.

Endocarditis

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. Antibiotic therapy, when used in large doses for extended periods, is effective in curing the bacterial infection of subacute bacterial endocarditis, but damage done to the heart by the bacteria cannot be repaired. Routine use of penicillin and other antibiotics during dental surgery and to treat primary bacterial infections has decreased the incidence of endocarditis.

Rheumatic Fever

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, malaise, and migratory arthritis, patients may develop nodules under the skin, skin rashes, abdominal pain, pleurisy, and chorea. The most serious aspect of the disease, however, is the involvement of the heart (carditis).

Treatment involves the use of penicillin to eradicate streptococci that may still be present, bed rest, and administration of salicylates or corticosteroids. It may take many weeks or months before the attack runs its course. Rheumatic fever has become relatively rare, probably due at least in part to the widespread use of antibiotics.

Tuberculosis

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 infected with TB will have developed a hypersensitivity to the TB bacteria even if they did not develop the disease. A purified protein derived from the bacteria is injected into the skin. The skin area is inspected 48 to 72 hours later for a bump. A positive test implies that TB infection has occurred. Skin tests are not 100 percent accurate and they do not always indicate the presence of active disease.

General preventive measures can be taken to reduce the spread of TB in public places. Ventilation systems lessen the chance of infection by dispersing the bacteria. Ultraviolet lighting also reduces, but does not eliminate, the threat of infection by killing TB bacteria in confined spaces. Vaccines, such as the bacillus Calmette Guerin (BCG) vaccine, prepared from bacteria that have been weakened, are another preventive measure. The BCG vaccine is most effective in preventing childhood cases of TB.

With the advent of effective antibiotics for TB, drug therapy has become the cornerstone of treatment. Single-drug treatment often causes bacterial resistance to drugs. Therefore, all recommended therapies include multiple drugs given for at least 6 months, often for as long as 9 to 12 months. Adjustments to the treatments are made based on susceptibility of the bacterial strain. A combination of antibiotics, including isoniazid, rifampin, streptomycin, pyrazinamide, and ethambutol, is usually prescribed.