Gonorrhea

Gonorrhea, infectious sexually transmitted infection of humans, which primarily involves the mucous membranes of the urogenital tract. Characterized by a discharge of pus, it is caused by the gonococcus bacterium, Neisseria gonorrhoeae. The incubation period is two to seven days.

SYMPTOMS AND DIAGNOSIS

Gonorrhea is much more obvious in males, who develop an acute discharge of pus from the urethra. Scant at the start, it becomes progressively thicker and heavier and causes frequent urination, often with a burning sensation. Should the prostate become infected, the passage of urine is partly obstructed. In females the infection occurs in the urethra, the vagina, or the cervix. Although discharge and irritation of the vaginal mucous membranes may be severe, more often few or no early symptoms appear.

Gonorrhea can be diagnosed by examining discharge from the penis or vagina for the presence of bacteria. A urine test can also detect the presence of bacteria and it is a noninvasive way to check people who are not exhibiting symptoms. Treatment in the early stages is usually effective. If the disease is untreated in the male, the early symptoms may subside but the infection may spread to the testicles, causing sterility. In the untreated female the infection usually spreads from the cervix into the uterus and fallopian tubes, causing pelvic inflammatory disease (see Gynecology). Severe pain may occur, or the infection may linger with few or no symptoms, gradually damaging the tubes and rendering the woman sterile. In both sexes the gonococcus may enter the bloodstream, resulting in arthritis, heart inflammation, or other diseases. Gonorrhea in pregnant women may be transmitted to the infant during birth and may, if untreated, cause a serious eye infection.

TREATMENT

Antibiotics are commonly used against gonorrhea, although over the years an increasing number of antibiotic-resistant strains of the gonorrhea bacteria have developed, causing a rise in the incidence of the disease in the 1990s. Still effective are antibiotics that are administered in a single dose, including ceftriaxone, cefixime, ciprofloxacin, and ofloxacin.

Equine Encephalomyelitis

Equine Encephalomyelitis is an infectious disease observed originally in horses and subsequently in humans, other mammals, and birds. A type of encephalitis occurring epidemically, it is caused by a virus that attacks the central nervous system. The disease is transmitted by mosquitoes and possibly by other bloodsucking insects. Three strains of the causative virus have been identified. Two of the strains are confined to North America; one causes a rare but severe type of the disease common to the east, and the other a milder type common to the west. The third strain is responsible for a type that occurs in Venezuela. Each type is characterized by inflammation of the brain and spinal cord, with high fever, headache, muscle pains, and sometimes convulsions as the earliest symptoms. Within one or two days after onset of the disease, somnolence develops, often progressing to coma.

Equine encephalomyelitis can be controlled by annual vaccination of horses and mules before the advent of summer. An antiserum vaccine administered in the early stages of the disease is sometimes effective in the treatment of infected animals. The disease in humans is known popularly as sleeping sickness. A vaccine made from infected chick embryos gives temporary immunity to the disease.

Diphtheria

Diphtheria, an acute and highly infectious disease, affecting children particularly, characterized by the formation of a false membrane in the passages of the upper respiratory system. The cause of the disease is Corynebacterium diphtheria, a bacillus discovered in 1883.

The diphtheria bacilli enter the body through the mouth and nose and attack the mucous membranes, where they multiply and secrete a powerful toxin. The toxin damages the heart and central nervous system, and can lead to death. Beginning about five days after exposure to diphtheria, a gray-white exudate is formed where the bacteria attack the walls of the nose and throat. This exudate increases in size and thickness, becoming a grayish false membrane, and it may block the air passages. Surgery may be necessary to prevent asphyxiation.

The universal use of antitoxin in treatment has cut the mortality rate to approximately 5 percent. Even more effective has been the development of harmless forms of diphtheria toxin, called toxoids. Given to infants during the first year of life as part of a combined injection, these toxoids immunize the children against serious infection and have drastically reduced the incidence of diphtheria.

The Schick test, used to determine whether an individual is immune or susceptible to diphtheria, was developed by the Hungarian-American pediatrician Béla Schick in 1913.

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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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

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.

Relapsing Fever

Relapsing Fever, acute infectious disease caused by spirochetes of the genus Borrelia and transmitted by the bite of ticks of the genus Ornithodoros and of body lice. The course of the disease is characterized by an incubation period of 3 to 18 days; onset of the acute stage begins with a chill followed by fever accompanied by headache, pains in the muscles and in the abdomen, and vomiting. The attack ends suddenly three to six days later, and the patient, although weak, is apparently recovering. After several more days, however, the acute stage recurs and lasts for three or four days. The patient then usually recovers, but in some cases one or more further recurrences may ensue; further relapses are most common in tick-borne relapsing fever.

Relapsing fever generally occurs in areas where poor nutrition and unhygienic conditions are prevalent; in times of famine the incidence of the disease may reach epidemic proportions. Treatment includes complete bed rest, a fluid diet, and tetracycline or chloramphenicol, usually taken orally.

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.

Hepatitis

Hepatitis, inflammation of the liver caused by viruses, bacterial infections, or continuous exposure to alcohol, drugs, or toxic chemicals, such as those found in aerosol sprays and paint thinners. Hepatitis can also result from an autoimmune disorder, in which the body mistakenly sends disease-fighting cells to attack its own healthy tissue, in this case the liver. No matter what its cause, hepatitis reduces the liver’s ability to perform life-preserving functions, including filtering harmful infectious agents from the blood, storing blood sugar and converting it to usable energy forms, and producing many proteins necessary for life.

Symptoms of hepatitis vary significantly depending on the cause and the overall health of the infected individual. Some cases of hepatitis have few, if any, noticeable symptoms. When symptoms are present, they may include general weakness and fatigue, loss of appetite, nausea, fever, and abdominal pain and tenderness. Another symptom is jaundice, a yellowing of the skin and eyes that occurs when the liver fails to break down excess yellow-colored bile pigments in the blood.

In acute hepatitis, symptoms often subside without treatment within a few weeks or months. About 5 percent of cases develop into an incurable form of the disease called chronic hepatitis, which may last for years. Chronic hepatitis causes slowly progressive liver damage that may lead to cirrhosis, a condition in which healthy liver tissue is replaced with dead, nonfunctional scar tissue. In some cases, cancer of the liver develops.

How STIs are Transmitted

STIs are transmitted by infectious agents—microscopic bacteria, viruses, parasites, fungi, and single-celled organisms called protozoa—that thrive in warm, moist environments in the body, such as the genital area, mouth, and throat. Most STIs spread during sexual intercourse (vaginal or anal), but other forms of sexual contact, such as oral sex, can also spread disease.

Some STIs are transmitted in ways other than by sexual contact. Certain viral STIs, such as AIDS and some types of hepatitis, may be transmitted by contact with infected blood. For instance, viral STIs may pass between people who share infected needles, and a person can become infected from a transfusion of infected blood. Some STIs may pass from an infected mother to her child. Infection may occur before birth, when the infectious agent crosses the placenta (organ in a pregnant woman’s uterus that links the blood supplies of mother and baby) and enters the baby’s bloodstream. Infection also may occur during childbirth, as the baby passes through the birth canal, or after birth, when the baby consumes infected breast milk. STIs cannot be transmitted through shaking hands or other casual contact, or through contact with inanimate objects such as clothing or toilet seats.

Sexually Transmitted Infections (STI)

Sexually Transmitted Infections (STIs), formerly known as venereal diseases, more than 25 infections passed from one person to another primarily during sexual contact. STIs are among the most common infections known—more than 15 million people in the United States become infected with one or more STIs every year. The United States has the highest STI rate in the industrialized world—roughly half of all Americans become infected with an STI before the age of 35. Despite the prevalence of STIs, studies show that many people are unaware of their risks for contracting an STI or the serious, and sometimes deadly, health consequences that may result from an untreated infection.

Some STIs, such as gonorrhea or chlamydia, may cause no symptoms. People who do not know they are infected risk infecting their sexual partners and, in some cases, their unborn children. If left untreated, these diseases may cause debilitating pain or may destroy a woman’s ability to have children. Some STIs can be cured with a single dose of antibiotics, but many, such as acquired immunodeficiency syndrome (AIDS), are incurable. People with these diseases remain infectious to others for their entire lives.

See also: How STI are Transmitted

Scarlet Fever

Scarlet Fever, infectious disease, caused by group A hemolytic streptococci, which also causes strep throat. The causative organism usually enters the body through the nose or mouth; it is transmitted from person to person by direct contact, that is, by sprays of droplets from the respiratory tract of an infected person, or by indirect contact through the use of utensils previously handled by an infected person. The disease most commonly affects children between the ages of two and ten.

The typical initial symptoms of the disease are headache, sore throat, chills, fever, and general malaise. From two to three days after the first appearance of symptoms, red spots may appear on the palate; bright red papilla emerge on the tongue, giving it an appearance commonly called strawberry tongue. A characteristic skin eruption appears on the chest and usually spreads over the entire body except the face. The rash fades on pressure. The fever, which frequently runs as high as 40° to 40.6° C (104° to 105° F), generally lasts only a few days but may extend to a week or longer. The rash usually fades in approximately a week, and at that time the skin begins to peel.

Scarlet fever may be complicated by an infection of the middle ear mastoids or sinuses, or even by pneumonia. See also Rheumatic Fever. Occasionally, inflammation of the kidneys (glomerular nephritis) may develop after scarlet fever. Since the introduction of penicillin, however, most instances of scarlet fever can be cured without the occurrence of permanent aftereffects.

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.

Leprosy

Leprosy or Hansen's Disease is a chronic infectious disease caused by the bacterium Mycobacterium leprae. Leprosy can be treated effectively with several drugs, but if left untreated, the disease can result in severe disfigurement, especially of the feet, hands, and face. It is rarely fatal.

Leprosy has long been one of the most feared diseases worldwide. The stigma attached to leprosy has often caused those who contracted the disease to be shunned by family, friends, and society.

Leprosy has two main forms, known as tuberculoid and lepromatous disease. In tuberculoid leprosy, the skin lesions are few and small, with only a few bacteria present in each. In lepromatous leprosy, the more severe form of the disease, the lesions may be much more widespread and contain many leprosy bacteria. As lepromatous leprosy progresses, hard nodules and folds of skin may form on the face and the nose may collapse, giving a person a characteristic lionlike appearance.

The symptoms of leprosy may be caused by proliferation of the bacteria in lepromatous leprosy or by the body’s immune response to the bacteria in tuberculoid leprosy. In both forms of leprosy, there is usually some degree of irreversible nerve damage resulting from either of these two processes. Because of the lack of sensation in affected areas of the skin, people with leprosy often do not notice burns and injuries to their fingers and toes and fail to treat them. These injuries can then become infected with other types of bacteria that cause tissue damage. Gradually, damaged tissue and bone are resorbed by the body, causing the digits to become shorter. However, leprosy does not, as myth would have it, cause parts of the body to fall off. Damage to nerves in the hands and feet may also cause the fingers and toes to become stiff and curl inward, and some patients become unable to walk. Both forms of the disease may also lead to blindness.

The first effective drug for treating leprosy, called promin, was developed in the mid-1940s. Within several years, painful daily promin injections were replaced with oral doses of a related drug, called dapsone. By the early 1980s, strains of the leprosy bacterium resistant to dapsone had become widespread, and multidrug therapy, a combination of several medications, became necessary to treat the disease. Three antibiotics, dapsone, rifampin, and clofazimine, are currently used to treat leprosy. The drugs must be taken for a long period, typically six months in cases of tuberculoid leprosy and two years for lepromatous leprosy. Treating leprosy using multidrug therapy is much more effective than using any one drug alone, and this treatment helps ensure that a drug-resistant form of the leprosy bacterium will not develop. These drugs cannot reverse the nerve damage and deformities of the hands, feet, and face that are characteristic of the disease. However, they can often halt the progression of the disease and help prevent it from being passed on to anyone else.

Cholera

Cholera, severe infectious disease endemic in India and some other tropical countries and occasionally spreading to temperate climates. The symptoms of cholera are diarrhea and the loss of water and salts in the stool. In severe cholera, the patient develops violent diarrhea with characteristic “rice-water stools,” vomiting, thirst, muscle cramps, and sometimes circulatory collapse. Death can occur as quickly as a few hours after the onset of symptoms. The mortality rate is more than 50 percent in untreated cases, but falls to less than 1 percent with proper treatment.

Treatment consists mainly of intravenous or oral replacement of fluids and salts. Packets for dilution containing the correct mixture of sodium, potassium, chloride, bicarbonate, and glucose have been made widely available by the WHO. Most patients recover in three to six days. Antibiotics such as tetracyclines, ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole can shorten the duration of the disease.

A vaccine made from killed bacteria is commercially available and offers partial protection for a period of three to six months after immunization. Experimental studies have shown that the cholera bacterium produces a toxin that causes the small intestine to secrete large amounts of fluid, which leads to the fluid loss characteristic of the disease. This has led to work on a vaccine containing inactivated toxin. Attempts are also being made to develop a vaccine containing live bacteria that have been altered so that they do not produce the toxin.