Influenza

Influenza, also known as flu, contagious infection primarily of the respiratory tract. Influenza is sometimes referred to as grippe. Influenza is caused by a virus transmitted from one person to another in droplets coughed or sneezed into the air. It is characterized by coldlike symptoms plus chills, fever, headaches, muscle aches, and fatigue. Most people recover completely in about a week. But some people are vulnerable to complications such as bronchitis and pneumonia. This group includes children with asthma, people with heart or lung disease, and the elderly. In the United States, people age 65 and older account for about 90 percent of influenza-associated deaths.

Because influenza is highly contagious and spreads easily, it usually appears as epidemics—that is, outbreaks involving many people. If an outbreak spreads around the world—not uncommon in this age of rapid international travel—it is called a pandemic.

Many millions of people develop the flu each year. In most years less than 1 percent of those infected die. Nonetheless, this translates into large numbers. The United States Centers for Disease Control and Prevention (CDC) estimates that influenza causes more than 20,000 deaths in the United States each year; combined, influenza and pneumonia are among the nation’s ten leading causes of death. During epidemics and pandemics, death rates soar. The influenza pandemic that occurred between 1918 and 1919—the worst on record—killed about 500,000 people in the United States and more than 20 million people worldwide.

Influenza Types

The word influenza is derived from the Latin word influentia. Italians in the early 16th century first applied the word influenza to outbreaks of any epidemic disease because they blamed such outbreaks on the influence of heavenly bodies. The first known use of the name specifically for the flu occurred in 1743 when an epidemic swept through Rome and its environs.

Today scientists know that members of the family Orthomyxoviridae, a group of viruses that infect vertebrate animals, cause influenza. The virus consists of an inner core of the genetic material ribonucleic acid (RNA) surrounded by a protein coat and an outer lipid (fatty) envelope from which project spikes of proteins called hemagglutinin and neuraminidase. These proteins act as antigens—that is, they elicit an immune response in the human or other host organism that the virus invades. In addition to their role as antigens, hemagglutinin enables the virus to bind to and invade cells and neuraminidase allows the virus to move among cells.

There are three types of influenza viruses, known as A, B, and C. Type A, the most dangerous, infects a wide variety of mammals and birds. It causes the most cases of the disease in humans and is the type most likely to become epidemic. Type B infects humans and birds, producing a milder disease that can also cause epidemics. Type C apparently infects only humans. It typically produces either a very mild illness indistinguishable from a common cold or no symptoms at all. Type C does not cause epidemics.

Influenza type A and B viruses continually change. Some changes involve a series of genetic mutations that, over a period of time, cause a gradual evolution of the virus. Called antigenic drift, this process accounts for most of the changes in influenza viruses that occur from one year to the next. Other changes, less common but more injurious, involve abrupt changes in the hemagglutinin or neuraminidase. This type of change is called antigenic shift and results in a new subtype of the virus. Type A viruses undergo both kinds of transformations; influenza type B viruses apparently change only by the process of antigenic drift.

Scientists further differentiate virus subtypes into strains, generally named for the geographic area where they were first detected. For example, the strains that caused the most infections during the 2001-2002 flu season in the Northern Hemisphere were type A New Caledonia and Moscow strains and Type B Sichuan strain.

Once a person has been infected by a specific strain of influenza, he or she has built up immunity to that strain in the form of antibodies. The person’s immune system then can recognize the strain’s hemagglutinin or neuraminidase and attack them if they reappear. The antibodies offer some protection against antigenic drifts, but not against antigenic shifts. Thus, because the viruses continually change, they can cause repeated waves of infection, even among people previously infected.

Scientists do not understand exactly what causes antigenic shifts. One leading theory suggests that a human strain and an animal strain recombine to create a new strain. This strain has the ability to infect humans but has antigens on its surface that are unfamiliar to the human immune system.

Transmission of Influenza

Influenza viruses pass from person to person mainly in droplets expelled during sneezes and coughs. When a person breathes in virus-laden droplets, the hemagglutinin on the surface of the virus binds to enzymes in the mucous membranes that line the respiratory tract. The enzymes, known as proteases, cut the hemagglutinin in two, which enables the virus to gain entry into cells and begin to multiply. These proteases are common in the respiratory and digestive tracts but not elsewhere, which is why the flu causes primarily a respiratory illness with occasional gastrointestinal symptoms. In the 1990s scientists discovered that some flu strains also can use the enzyme plasmin to cut hemagglutinin. Plasmin is common throughout the body, enabling the flu strains to infect a variety of tissues.

Although an influenza epidemic can occur at any time of year, flu season in temperate regions typically begins with the approach of winter—November in the Northern Hemisphere, April in the Southern Hemisphere. Flu viruses spread more easily during cold weather because people tend to spend more time crowded together in homes and schools, as well as buses, subways, and other places with poor ventilation. An epidemic may be restricted to a town or city or may quickly spread geographically as infected people travel aboard motor vehicles, airplanes, and ships.

Symptoms and Diagnosis for Influenza

Influenza is an acute disease with a rapid onset and pronounced symptoms. After the influenza virus invades a person’s body, an incubation period of one to two days passes before symptoms appear. Classic symptoms include sore throat, dry cough, stuffed or runny nose, chills, fever with temperatures as high as 39º C (103º F), aching muscles and joints, headache, loss of appetite, occasional nausea and vomiting, and fatigue. For most people flu symptoms begin to subside after two to three days and disappear in seven to ten days. However, coughing and fatigue may persist for two or more weeks.

Death from influenza itself is rare. But influenza can aggravate underlying medical conditions, such as heart or lung disease. Invading influenza viruses produce inflammation in the lining of the respiratory tract, damage that increases the risk that secondary infections will develop. Common complications include bronchitis, sinusitis, and bacterial pneumonia, occurring most frequently in the elderly, people on chemotherapy, and people with acquired immunodeficiency syndrome (AIDS) or another disease that compromises the immune system. If properly treated, these complications seldom are fatal.

Because influenza is so common and exhibits standard symptoms, doctors often diagnose the illness based on the season and whether flu cases have recently been reported in the area. To prove a diagnosis of influenza in a patient, the virus must be isolated from the person’s nasal or cough secretions or blood and identified under a microscope.

Treatment and Prevention for Influenza

There is no specific cure for influenza. Recommended treatment usually consists of bed rest and increased intake of nonalcoholic fluids until fever and other symptoms lessen in severity. Certain drugs have been found effective in lessening flu symptoms, but medical efforts against the disease focus chiefly on prevention by means of vaccines that create immunity.

Drugs That Ease Symptoms
Vaccines

Pandemics and Historic Outbreaks

Evidence suggests that all influenza viruses in mammals, including humans, derived from viruses in wild ducks and other waterfowl. Some of these viruses could have been acquired by humans thousands of years ago. But medical historians know of no clearly identifiable influenza epidemics until large-scale outbreaks occurred in Europe in 1510, 1557, and 1580. The 1580 outbreak also spread into Africa and Asia, making it the first known pandemic. Pandemics have occurred periodically ever since. Major pandemics took place in 1729-1730, 1732-1733, 1781-1782, 1830-1831, 1833, and 1889-1890. The last of these, called the Russian flu because it reached Europe from the east, was the first pandemic for which detailed records are available.

In the 20th century, major pandemics occurred in 1918-1919, 1957-1958, and 1968-1969. The 1918-1919 pandemic was the most destructive in recorded history. It started as World War I (1914-1918) was ending and caused 20 million deaths—twice as many deaths as the war itself. When and where the pandemic began is uncertain, but because Spain experienced the first major outbreak, the disease came to be called the Spanish flu. The virus was exceptionally lethal; many of the deaths were among young adults age 20 to 40, a group usually not severely affected by influenza.

In 1957 a flu outbreak occurred in Guizhou, a province in southwestern China. Within six months, most areas of the world were battling what became known as Asian flu. Before the 1957-1958 pandemic subsided, an estimated 10 to 35 percent of the world’s population had been affected. The overall mortality rate, however, was comparatively low.

About a decade later, a variant of the virus that caused the 1957-1958 pandemic originated in either Guizhou or Yunnan province in southern China. The variant was first isolated and identified in Hong Kong in July 1968. Within a few months, cases of this Hong Kong flu appeared around the world. Hardest hit by the pandemic were children under age 5 and adults aged 45 to 64. In the United States, an estimated 30 million people were infected and there were some 33,000 influenza-related deaths.

No additional pandemics occurred during the 20th century, but public health experts expect that there will be more pandemics in coming years. While scientists do not yet know how to accurately predict flu outbreaks, they have established an international network to track and monitor outbreaks so that health officials can take immediate preventive measures to avoid pandemics. The international network, called FluNet, consists of about 110 influenza centers in more than 80 countries and several World Health Organization (WHO) centers, all linked electronically.

Influenza Research

By the late 1890s and early 1900s, scientists understood that microorganisms caused disease. Most disease research focused on bacteria, which are large enough to be visible under a light microscope and can be isolated using filters. But technology at the time prevented scientists from identifying a disease-causing agent as small as a virus.

In the 1890s German bacteriologist Richard F. J. Pfeiffer reported that he had identified the bacterium Haemophilus influenzae as the cause of influenza. Further investigation indicated, however, that this bacterium was not always present in people with influenza. Scientists concluded that the Haemophilus influenzae bacterium probably played a role in secondary infections.

Meanwhile, the long-held belief that influenza only occurred in humans was overturned. Around 1930 American bacteriologist Richard E. Shope showed that it was possible to transfer an influenza-like disease from one pig to another. Thereafter scientists chiefly used animals in their research on influenza.

In 1933 English physicians Wilson Smith, Christopher H. Andrewes, and Patrick P. Laidlaw removed secretions from the throat of a human flu victim, filtered out a suspect infectious agent, and injected the material into ferrets. The ferrets then developed influenza, thereby demonstrating that the infectious agent caused influenza. Research performed by other researchers eventually proved that the infectious agent was the influenza A virus. The influenza B virus was isolated in 1940, and the influenza C virus in 1950.

In 1941 scientists demonstrated that a vaccine could control influenza. The first vaccine was developed to protect soldiers during World War II (1939-1945). Early influenza vaccines produced from the 1940s to the mid-1960s were all made from killed viruses, which cannot cause infection. But these early vaccines contained impurities that produced fever, headaches, and other severe side effects. Improved pharmaceutical procedures have made today’s vaccines almost free from impurities, greatly reducing the chance that the vaccines will cause side effects.

Despite these improvements, developing influenza vaccines remains a challenge. Current vaccines do not provide 100 percent protection against influenza, and they can be quickly rendered ineffective by changes in the viruses themselves. Some scientists, believing that vaccines will never be able to completely control influenza, work to expand the number and variety of drugs available to treat the disease once symptoms appear. Until a cure for influenza is discovered, public health officials hope that identifying and reporting new viral strains quickly will result in timely actions that prevent the recurrence of deadly pandemics. Even in best-case scenarios, however, influenza is expected to remain a formidable opponent of human health.

Entrepreneur

Entrepreneur, one who assumes the responsibility and the risk for a business operation with the expectation of making a profit. The entrepreneur generally decides on the product, acquires the facilities, and brings together the labor force, capital, and production materials. If the business succeeds, the entrepreneur reaps the reward of profits; if it fails, he or she takes the loss.

The Austrian-American economist Joseph A. Schumpeter stressed the role of the entrepreneur as an innovator, the person who develops a new product, a new market, or a new means of production. One important example was Henry Ford. In the industrialized economies of the late 20th century, giant corporations and conglomerates have largely replaced the individual owner-operator. There is still a place for the entrepreneur, however, in small businesses as well as in the developing economies of the Third World nations.

NEW DIRECTIONS IN WEIGHT CONTROL

The weight-loss goal of most obese dieters is to achieve an ideal weight often defined by celebrities and models in fashion magazines. But research over the last decade indicates that a 5- to 10-percent reduction in body weight is sufficient to significantly improve medical conditions associated with obesity, such as hypertension, diabetes mellitus, and elevated cholesterol levels. These health improvements occur even though patients may still be overweight.
These new weight-loss goals may be difficult for obese people to accept. Obese people often seek weight-loss goals that may be biologically impossible to achieve or, if achieved, cannot be maintained. One study of overweight women found that the average weight goal was a 30 percent reduction in body weight. Yet no obesity treatment produces long-term, maintainable weight losses significant enough for patients to reach this goal. Physicians and commercial weight-loss programs need to help obese people feel successful when more modest reductions in weight and significant improvements in health are achieved, many health experts believe.

OBESITY

OBESITY, medical condition characterized by storage of excess body fat. The human body naturally stores fat tissue under the skin and around organs and joints. Fat is critical for good health because it is a source of energy when the body lacks the energy necessary to sustain life processes, and it provides insulation and protection for internal organs. But the accumulation of too much fat in the body is associated with a variety of health problems. Studies show that individuals who are overweight or obese run a greater risk of developing diabetes mellitus, hypertension, coronary heart disease, stroke, arthritis, and some forms of cancer.

MEASURING OBESITY

The body mass index (BMI) is commonly used to determine desirable body weights. BMI is a measure of an adult’s weight in relation to height, and it is calculated metrically as weight divided by height squared (kg/m2). People with a BMI of 25.0 to 29.9 are considered overweight and people with a BMI of 30 or above are considered obese .

Body mass index only provides a rough estimate of desirable weight, however. Physicians recognize that many other factors besides height affect weight. Weight alone may not be an indicator of fat, as in the case of a bodybuilder who may have a high BMI because of a high percentage of muscle tissue, which weighs more than fat. Likewise, a person with a sedentary lifestyle may be within a desirable weight range but have excess fat tissue. In general, however, the higher the BMI, the greater the risk for developing serious medical conditions.

CAUSES OF OBESITY

A calorie is the unit used to measure the energy value of food and the energy used by the body to maintain normal functions. When the calories from food intake equal the calories of energy the body uses, weight remains constant. But when a person consumes more calories than the body needs, the body stores those additional calories as fat, causing subsequent weight gain. Consuming about 3,500 calories more than what the body needs results in a weight gain of 0.45 kg (1 lb) of fat.

TREATMENTS FOR OBESITY

Obesity can become a chronic lifelong condition caused by overeating, physical inactivity, and even genetic makeup. No matter what the cause, however, obesity can be prevented or managed with a combination of diet, exercise, behavior modification, and in severe cases, weight-loss medications and surgery.

Diets

The most common and conservative treatment for obesity utilizes a nutritionally balanced, low calorie diet. Most health-care professionals and commercial weight-loss programs recommend diets consisting of 1,200 to 1,500 calories per day, usually in the following proportions: 60 percent carbohydrate, 30 percent fat, and 10 percent protein. Research from university obesity treatment centers indicates that patients who follow a low calorie diet lose 10 percent of their initial weight in 20 weeks. Without further treatment, however, patients usually regain one-third of the weight in the following year.

A more aggressive approach for persons who are more than 20 kg (40 lb) overweight includes very low calorie diets ranging from 400 to 800 calories per day. These diets are usually based on four to five servings of a liquid formula each day. Candidates must be carefully screened and medically supervised while on the diet. People on very low calorie diets lose approximately 15 to 20 percent of their initial body weight in 16 weeks. Once they go off a very low calorie diet, they typically regain approximately one-half of that weight within a year.

Meal replacements are liquid shakes or portion-controlled meals that are substituted for one or two meals a day. They are typically used as part of a 1,200 to 1,500 calorie diet. Studies have shown that meal replacements are often more effective than very low calories diets, resulting in an increase in the amount of initial weight loss and enabling dieters to maintain their weight loss. Unlike very low calorie diets, meal replacements do not require that candidates receive extensive medical monitoring.

Exercise

Caloric restriction alone will not produce long-term weight loss. While the data from studies on the effect of exercise for short-term weight loss are contradictory, research clearly indicates that regular exercise is the single best predictor for achieving long-term weight control. Regular exercise will also improve some of the medical conditions associated with obesity, including elevated blood cholesterol, hypertension, and diabetes mellitus.

Behavior Modification

Many eating and exercise habits combine to promote weight gain. Certain times, places, activities, and emotions may be linked to periods of overeating or inactivity. Many obesity treatment programs recommend individuals keep a food diary that records all food or drink consumed, when and with whom it was consumed, and the mood or precipitating events that trigger eating. After one to two weeks, the diary may reveal a pattern of activities or negative emotions that lead to overeating. Once these eating cues are identified, techniques can be developed and practiced to prevent unwanted eating habits.

Weight-Loss Medications

Weight-loss medications of any type are only appropriate for people with a BMI of 30 or above, or a BMI of 27 or above accompanied by weight-related medical conditions such as diabetes mellitus or hypertension. Amphetamine drugs were formerly prescribed to combat obesity, but their well-documented side effects, including insomnia, anxiety, and tolerance (the need to take higher and higher doses to continue to produce the same effect), made them less popular by the late 1970s.

A renewed scientific and commercial interest in weight-loss medications was prompted by the approval by the Food and Drug Administration (FDA) of the appetite suppressant dexfenfluramine (sold under the brand name Redux) in 1996. Dexfenfluramine was the first weight-loss medication approved in the United States in over 20 years and the first ever approved for maintaining weight loss. Although never approved for long-term use by the FDA, a combination of two drugs, phentermine and fenfluramine, or phentermine and dexflenfluramine, popularly known as fen-phen, was used by millions of Americans to promote weight loss. Fenfluramine and dexfenfluramine were eventually associated with valvular heart disease, and the manufacturer withdrew these medications from the marketplace in 1997.

The FDA has approved two medications, sibutramine and orlistat, for long-term use in the treatment of obesity. Sibutramine (sold under the brand name Meridia) increases fullness, making the required dietary changes for weight loss and the maintenance of weight loss easier to accomplish. Unlike dexfenfluramine and fenfluramine, sibutramine does not appear to be associated with valvular heart disease, although a small number of patients may develop significant increases in blood pressure. Orlistat (sold under the brand name Xenical) works by blocking the absorption of fat. Scientists are also investigating the hormone leptin, which plays a role in obesity in mice, as a possible treatment for obesity in humans.

Over a six-month period, weight-loss medications may result in a 10-percent body weight reduction. Weight loss slows or stops after six months, and discontinuing medication usually causes weight regain. The continued use of medications keeps most of the lost weight from returning for two years. Many experts recommend that medications for weight control be used continuously, like medications for diabetes mellitus and hypertension. Unfortunately, few studies have examined the consequences of long-term use of weight-control medications.

Surgery

Surgery may be a weight-loss option for patients who are severely obese (with a BMI of 40 or above) and suffer from serious medical complications due to weight. While the number of people in the United States who qualify for surgery remains small, the percentage of Americans with a BMI of 40 or above increased from less than 1 percent in 1990 to 2.2 percent in 2000.

There are two accepted surgical procedures for reducing body weight: gastroplasty and gastric bypass. Although these two procedures use different surgical methods, they both reduce the stomach to a pouch that is smaller than a chicken’s egg, drastically limiting the amount of food that can be consumed at one time. Surgery produces 25 to 35 percent reductions in weight over the first year and most of this weight loss is maintained five years after surgery. More importantly, the serious medical conditions that accompany extreme obesity improve significantly. Surgery is not without risk and should be performed by skilled surgeons who also provide patients with a comprehensive program for long-term weight control.

The Seven Wonders of the World

The Seven Wonders of the World were works of art and architecture considered by the ancient Greeks and Romans to be the most fabulous creations of antiquity. They were the Pyramids of Egypt, The Hanging Gardens of Babylon, The Temple of Artemis, The Statue of Zeus, The Mausoleum of Halicarnassus, The Colossus of Rhodes, and The Pharos of Alexandria.

1. Temple of Artemis-The Temple of Artemis is depicted in a fanciful reconstruction based on an Italian Renaissance church in this hand-colored engraving by Dutch artist Maarten van Heemskerck. Built in Ephesus in Asia Minor in 356 bc, the Greek temple was considered to be one of the Seven Wonders of the World. It was destroyed by the Goths in ad 262.

2. Colossus of Rhodes-The Colossus of Rhodes, depicted in this hand-colored engraving by Maarten van Heemskerck, was built about 280 bc. Standing 30 m (100 ft) high, it was built to guard the entrance to the harbor at Rhodes. The ancient Greeks and Romans considered it to be one of the Seven Wonders of the World.

3. Pharos of Alexandria-The Pharos of Alexandria, an ancient lighthouse, is depicted in this hand-colored engraving by Maarten van Heemskerck. The lighthouse stood on an island in the harbor of Alexandria and was over 134 m (440 ft) tall. It was considered to be one of the Seven Wonders of the World.

4. Hanging Gardens of Babylon -This hand-colored engraving by 16th century Dutch artist Maarten van Heemskerck depicts the Hanging Gardens of Babylon, one of the Seven Wonders of the World. Technically, the gardens did not hang, but grew on the roofs and terraces of the royal palace in Babylon. Nebuchadnezzar II, the Chaldean king, probably built the gardens in about 600 bc as a consolation to his Median wife who missed the natural surroundings of her homeland.

5. Mausoleum of Halicarnassus-The Mausoleum of Halicarnassus, depicted in this hand-colored engraving by Maarten van Heemskerck, was built about 353 bc. The mausoleum was a huge marble tomb built for King Mausolus of Caria in Asia Minor. It was considered to be one of the Seven Wonders of the World.

6. Statue of Zeus -The Greek sculptor Phidias created the 12-m (40-ft) tall Statue of Zeus in about 435 bc. The statue, depicted in this engraving by 16th-century Dutch artist Maarten van Heemskerck, stood in Olympia and was perhaps the most famous sculpture in ancient Greece. Phidias made the god’s robe and ornaments from gold and carved the body out of ivory.

7.Pyramids of Egypt-Of the Seven Wonders of the World, the famous pyramids located in Giza, near the city of Cairo, Egypt, are the only ones remaining nearly intact. They are depicted here in an engraving by 16th-century Dutch artist Maarten van Heemskerck.

Mona Lisa

Mona Lisa (1503-1506), painted by the Italian artist Leonardo da Vinci, was also known as La Gioconda, possibly referring to the subject’s husband, banker Zanobi del Giocondo. The artist’s use of very deep space in the background with a close-in portrait is typical of Renaissance painting style. The painting hangs in the Louvre, Paris.

Statue of Liberty

The Statue of Liberty, a symbol of freedom for many, was one of the first sights to welcome immigrants arriving in the United States. The statue stands 93 m (305 ft) tall on Liberty Island in New York Harbor. It was designed by French sculptor Frédéric-Auguste Bartholdi and is a gift from France commemmorating the first centennial of U.S. independence from Britain.