yellow fever, acute infectious disease endemic in tropical Africa and many areas of South America. Epidemics have extended into subtropical and temperate regions during warm seasons. In 1878 a severe outbreak in the Mississippi Valley killed about 20,000; the last epidemic in the United States occurred in New Orleans in 1905. Yellow fever is caused by a virus transmitted by the bite of the female Aedes aegypti mosquito, which breeds in stagnant water near human habitations. A form of the disease called sylvan yellow fever is transmitted in tropical jungles by other species of mosquitoes that live in trees.

At the end of the 19th cent., yellow fever was highly prevalent in the Caribbean, and a way of controlling it had to be found before construction of the Panama Canal could be undertaken. In 1900 an American commission headed by Walter Reed and including James Carroll, Jesse Lazear, and Aristides Agramonte gathered in the U.S. Army's Camp Columbia in Cuba. Through their experiments they proved the theory of C. J. Finlay that yellow fever was a mosquito-borne infection. Within the next few years, W. C. Gorgas, an army physician and sanitation expert, succeeded in controlling the disease in the Panama Canal Zone and other areas in that part of the world by mosquito-eradication measures. The later development of an immunizing vaccine and strict quarantine measures against ships, planes, and passengers coming from known or suspected yellow-fever areas further aided control of the disease.

Yellow fever begins suddenly after an incubation period of three to five days. In mild cases only fever and headache may be present. The severe form of the disease commences with fever, chills, bleeding into the skin, rapid heartbeat, headache, back pains, and extreme prostration. Nausea, vomiting, and constipation are common. Jaundice usually appears on the second or third day. After the third day the symptoms recede, only to return with increased severity in the final stage, during which there is a marked tendency to hemorrhage internally; the characteristic "coffee ground" vomitus contains blood. The patient then lapses into delirium and coma, often followed by death. During epidemics the fatality rate was often as high as 85%. Although the disease still occurs, it is usually confined to sporadic outbreaks.

valley fever: see coccidioidomycosis.

undulant fever: see brucellosis.

typhoid fever acute, generalized infection caused by Salmonella typhi. The main sources of infection are contaminated water or milk and, especially in urban communities, food handlers who are carriers. The symptoms of typhoid appear 10 to 14 days after infection; they include high fever, rose-colored spots on the abdomen and chest, diarrhea or constipation, and enlargement of the spleen. Complications, especially in untreated patients, may be numerous, affecting practically every body system, and they account for the mortality rate of 7% to 14%. Perforation of the intestine with hemorrhage is not uncommon. Chloramphenicol is the most effective drug in combating typhoid, and in very toxic patients a cortisone derivative may be helpful. Skilled nursing care is still of the utmost importance, as is a high caloric diet to prevent wasting of the body. Vaccination against typhoid is a valuable preventive measure, especially for persons in military service and for those who travel to poorly sanitized regions.

trench fever: see rickettsia.

swine fever: see hog cholera.

swamp fever: see leptospirosis.

snail fever: see schistosomiasis.

scarlet fever or scarlatina, an acute, communicable infection, caused by group A hemolytic streptococcal bacteria (see streptococcus) that produce an erythrogenic toxin. The disease is now uncommon, probably because antibiotic therapy has lessened the likelihood of spread. It occurs in young children, usually between two and eight years of age, and is spread by droplet spray from carriers and from individuals who have contracted the disease. The incubation period is from three to five days, and infectivity lasts about two weeks. Scarlet fever may be mild or severe, but it is rarely fatal if treated. Typical symptoms are sore throat, headache, fever, flushed face with a ring of pallor about the mouth, red spots in the mouth, coated tongue with raw beefy appearance and inflamed papillae underneath it (strawberry tongue), and a characteristic eruption on the body. The streptococcal bacterium that causes scarlet fever is identical to the streptococcal pharyngitis (strep throat) organism, the difference being the production of a toxin to which the patient is susceptible in the case of scarlet fever. Severe infections are occasionally complicated by rheumatic fever, kidney disease, ear infection, pneumonia, meningitis, or encephalitis. Mild scarlet fever requires only bed rest, antibiotics, analgesics or antipyretics, and symptomatic treatment. Antibiotics, immune serum, and antitoxin may be required for severe cases.

rheumatic fever, systemic inflammatory disease, extremely variable in its manifestation, severity, duration, and aftereffects. It is frequently followed by serious heart disease, especially when there are repeated attacks. Rheumatic fever usually affects children. It is closely related to a preceding streptococcal infection (e.g., streptococcal tonsillitis or pharyngitis). Some of its symptoms are tenderness and inflammation about the joints, fever, jerky movements, nodules under the skin, and skin rash. If inflammation of the heart, or myocarditis, is mild, there is no permanent heart damage, but if the valves of the heart become inflamed, they may become scarred and deformed, permanently impairing their function. Such heart damage can sometimes be corrected by surgery.

Treatment of rheumatic fever is with penicillin, salicylates, and steroids; extended rest is usually necessary. Rheumatic fever may be prevented by prompt treatment of all streptococcal infections. Cardiac damage may possibly be avoided if prophylactic measures are taken after a first attack of rheumatic fever, i.e., long-term maintenance doses of antibiotics, to discourage streptococcal infections and recurrences of rheumatic fever. Rheumatic fever has declined in incidence in the industrialized countries, but has increased in prevalence in the Third World. See also streptococcus.

rabbit fever: see tularemia.

parrot fever: see psittacosis.

hemorrhagic fever, any of a group of viral diseases characterized by sudden onset, muscle and joint pain, fever, bleeding, and shock from loss of blood. Bleeding occurs in the form of leakage from capillaries in the internal organs and the skin and mucous membranes. The causative viruses may be transmitted to humans by insects, ticks, or rodents, but in the case of the African hemorrhagic fevers, Ebola and Marburg, the animal carrier is unknown. In addition to Ebola and Marburg, well-known hemorrhagic fevers include hantavirus, Lassa fever, yellow fever, and a severe form of dengue called dengue hemorrhagic fever (see dengue fever; see also Ebola virus).

Ebola and Marburg are closely related, newly emergent viruses that have in recent years caused epidemics in central Africa, with very high rates of mortality. Hantavirus occurs in many different parts of the world and is spread to humans from field rodents via microscopic bits of their excretions that get into the air and are inhaled. It was originally known as a disease of Asia and Europe that primarily attacked the kidneys, but a more deadly pulmonary form of hantavirus infection has more recently caused numerous fatalities in the United States, Chile, and other countries. Lassa fever, also spread to humans from rodent excretions, occurs primarily in W Africa. Closely related to the Lassa virus are the Junin and Machupo viruses, which have caused outbreaks of hemorrhagic fever in South America. Yellow fever, transmitted by the bite of a mosquito, still occurs in tropical areas despite largely successful control efforts. Dengue hemorrhagic fever, also spread by mosquitoes, has in recent years caused many fatalities among children in tropical countries.

There is usually no specific treatment to combat the viruses that cause hemorrhagic fevers. An exception is the drug ribavirin, which has been effective in treating Lassa fever. Treatment generally consists of such supportive measures as the replacement of lost blood, the maintainence of fluid balance, and the alleviation of symptoms. Survival depends largely upon the virulence of the virus strain and the quality of treatment.

hay fever, seasonal allergy causing inflammation of the mucous membranes of the nose and eyes. It is characterized by itching about the eyes and nose, sneezing, a profuse watery nasal discharge, and tearing of the eyes. The cause is a sensitivity to one or more species of pollens or fungi. In addition, many patients with hay fever develop other allergic conditions, e.g., asthma and sinusitis. In the spring, hay fever may be caused by tree pollens (oak, elm, maple); in summer, by grass pollens, wheat or corn rusts, or fungus spores; in late summer and fall, by ragweed pollen, which is the most common cause. Temporary relief of symptoms may be obtained from antihistamines and decongestants, such as ephedrine. Physicians may resort to corticosteroids in severe cases. Sometimes desensitization measures are taken, consisting of repeated injections of small amounts of the allergen (pollen) until its presence produces no symptoms; however, the treatment must be continued from year to year, since immunity is not permanent. Some relief can be obtained by removing pollen from the air by air conditioners and filters.

fever blister: see herpes simplex.

fever, elevation of body temperature above the normal level, which in humans is about 98°F; (37°C;) when measured orally. Fever is considered to be a symptom of a disorder rather than a disease in itself. Under normal conditions the heat that is generated by the burning of food by the body is dissipated through such processes as perspiration and breathing. It is believed that infectious disease, injury to the body tissues, and other conditions that cause fever somehow trigger a disturbance in the functioning of the hypothalamus, the center of temperature control in the body. The rise in temperature is thought to be one of the body's defenses against infection: it may kill bacteria that cause disease or it may increase the rate at which the body's defenses fight infection. The effects of fever on the body are weakness, exhaustion, and sometimes a depletion of body fluids through excessive perspiration. Extremely high fevers may cause convulsive reactions and eventual death. In addition to infectious diseases (such as pneumonia and tonsillitis), disorders of the brain, certain types of cancer, and severe heatstroke may cause fever. There are also cases of fever where the cause cannot be detected. Treatment includes increasing the intake of fluids and administering aspirin and other fever-reducing medications. Aspirin may be dangerous in fevers of children because of Reye's syndrome. However, primary treatment is directed at the underlying cause unless the fever is very high (above 104°F;/40°C;). Persons with such dangerously high fevers are sometimes sponged with cool water or immersed in cool baths.

dengue fever, acute infectious disease caused by four closely related viruses and transmitted by the bite of the female Aedes mosquito; it is also known as breakbone fever and bone-crusher disease. The disease occurs in both epidemic and sporadic form in warm climates (S United States, South America, the E Mediterranean countries, India, and especially SE Asia and the W Pacific). The classic symptoms, following an incubation period of five to eight days, are high fever, chills, severe headache, pain in the joints, pain behind the eyes, rash, sweating, and prostration, but infected persons may experience milder symptoms. Symptoms subside in two to four days, but after a remission lasting from a few hours to two days there is another rise in temperature, and a generalized rash appears. Convalescence is sometimes prolonged, with weakness and low blood pressure.

Dengue hemorrhagic fever, a severe form of the disease, can cause hemorrhage, shock, and encephalitis. It occurs when a person who has acquired immunity to one of the viruses that cause dengue fever is infected by a different dengue virus. It is a leading cause of death among children in Southeast Asia and in recent years has become increasingly prevalent in tropical America. There is no specific treatment for dengue fever except good nursing care. Both diseases can be controlled by eradicating the mosquitoes and destroying their breeding places.

breakbone fever: see dengue fever.

beaver fever: see giardiasis.

Tsutsugamushi fever: see typhus.

Rocky Mountain spotted fever, infectious disease caused by a rickettsia. The germ is harbored by wild rodents and other animals and is carried by infected ticks that attach themselves to humans. Despite its name, Rocky Mountain spotted fever is most prevalent in the S United States from Virgina, the Carolinas, and Georgia W to Oklahoma; it may be encountered in other tick-infested regions. Symptoms include chills and high fever; a rose-colored skin rash that appears first on the wrists and ankles and spreads to the trunk, the spots turning deep red and running together; headache; and pains in the back, muscles, and joints. In severe cases there may be delirium or coma. Spotted fever is a serious disease; however, it is not usually fatal if prompt antibiotic treatment is administered. Immunization with vaccine is effective.

Q fever: see rickettsia.

Mediterranean fever: see brucellosis.

Malta fever: see brucellosis.

Lassa fever, a severe viral disease occurring mostly in W Africa, characterized by high fever, muscle aches, mouth ulcers, and bleeding in the skin. The disease was first recognized in Lassa, Nigeria, in 1969. The causative virus belongs to a group called arenaviruses and is harbored by a rat, Mastomys natalensis. The virus is spread to humans via the rat's urine in airborne droplets or contaminated food. The disease can also be caught by medical personnel treating patients in hospitals.

The incubation period of Lassa fever is 3 to 17 days. Following fever and general malaise, later stages of the disease may include abdominal pain, diarrhea, vomiting, and petechiae, tiny purplish spots in the skin caused by leakage of blood from the capillaries. Heart and kidney failure may also occur in severe cases, and mortality is high, ranging from about 15% to, among pregnant women, as much as 60%. Treatment by injection of the antiviral drug ribavirin is often successful if begun early.

See also hemorrhagic fever.

Acute infectious tropical disease, sometimes occurring in temperate zones. Abrupt onset of headache, backache, fever, nausea, and vomiting is followed by either recovery with immunity or by higher fever, slow pulse, and vomiting of blood. Patients may die in a week. Jaundice is common (hence the name). One of the world's great plagues for 300 years, it is caused by a virus transmitted by several species of mosquitoes. Carlos Finlay suggested and Walter Reed proved this means of spread, leading to near elimination of the disease through mosquito control (see William Gorgas). Treatment consists of supportive care, particularly fever reduction. Control of mosquitoes near cities and live-virus vaccines—developed by Max Theiler (1899–1972), who won a 1951 Nobel Prize for his work—have made yellow fever completely preventable.

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or Malta fever or Mediterranean fever or undulant fever

Infectious disease of humans and domestic animals. It is characterized by gradual onset of fever, chills, sweats, weakness, and aches, and it usually ends within six months. It is named after the British physician David Bruce (b. 1855—d. 1931), who first identified (1887) the causative bacteria. Three main species in the genus Brucella commonly cause the disease in humans, who contract it from infected animals (goats, sheep, pigs, cattle). Brucellosis is rarely transmitted between humans but spreads rapidly in animals, causing severe economic losses. Drug therapy is not practical for animal brucellosis, but vaccination of young animals is useful. Infected animals must be removed from herds. Antibiotics are effective against acute disease in humans, in whom it can cause liver and heart problems if untreated.

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or typhoid fever

Acute infectious disease resembling typhus (and distinguished from it only in the 19th century). Salmonella typhi, usually ingested in food or water, multiplies in the intestinal wall and then enters the bloodstream, causing septicemia. Symptoms begin with headache, aching, and restlessness. High fever gradually develops, with delirium. A rash appears on the trunk. The sites where the bacilli multiplied become inflamed and may ulcerate, leading to intestinal bleeding or peritonitis. Patients become exhausted and emaciated; up to 25percnt die if not treated. Antibiotic treatment is effective. Patients can carry typhoid for weeks to months or years. Carriers can contaminate the food they handle. Prevention depends mainly on water and sewage treatment and excluding carriers from food-handling jobs.

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or swine fever

Often fatal viral disease of swine in Europe, North America, and Africa, transmitted by vehicles used to carry pigs, people dealing with them, and uncooked garbage in feed. Fever progresses to symptoms that include appetite loss; affected eyes and digestive tract; respiratory difficulty; rash; and inflamed mouth and throat. The pig moves reluctantly and staggers; later it cannot rise; coma follows. Antiserum is rarely effective. Survivors become chronically ill and can spread the virus. Illness must be reported, infected animals slaughtered, and quarantine instituted. A vaccine can control it. The African strain causes death sooner and has no effective prevention or treatment.

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Infectious disease of warm-blooded animals, caused by Bacillus anthracis, a bacterium that, in spore form, can retain its virulence in contaminated soil or other material for many years. A disease chiefly of herbivores, the infection may be acquired by persons handling the wool, hair, hides, bones, or carcasses of affected animals. Infection may lead to death from respiratory or cardiac complications (within 1–2 days if acute), or the animal may recover. In humans, anthrax occurs as a cutaneous, pulmonary, or intestinal infection. The most common type, which occurs as an infection of the skin, may lead to fatal septicemia (blood poisoning). The pulmonary form of the disease is usually fatal. Sanitary working environments for susceptible workers are critical to preventing anthrax; early diagnosis and treatment are also of great importance. In recent decades, various countries have attempted to develop anthrax as a weapon of biological warfare; many factors, including its extreme potency (vastly greater than any chemical-warfare agent), make it the preferred biological-warfare agent. Concerns about anthrax mounted in 2001 after it was found in letters mailed to members of the U.S. government and news agencies.

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or scarlatina

Acute infectious disease caused by some types of streptococcus bacteria. Fever, sore throat, headache, and, in children, vomiting are followed in two to three days by a rash. The skin peels in about one-third of cases. After a coating disappears, the tongue is swollen, red, and bumpy (strawberry tongue). Glands are usually swollen. Complications frequently involve the sinuses, ears (sometimes with mastoiditis), and neck. Abscesses are common. Nephritis, arthritis, or rheumatic fever may occur later. Treatment involves penicillin, bed rest, and adequate fluid intake. Scarlet fever has become uncommon and much milder since the mid-20th century, independent of the use of antibiotics.

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Generalized disease caused by certain types of streptococcus bacteria. It occurs mostly in children and young adults. Symptoms may be mild or severe. Sudden fever, joint pain, and inflammation may begin days to weeks after a streptococcal infection, usually of the throat (see pharyngitis). Other symptoms may include skin nodules and rashes, chorea, abdominal pain, nosebleeds, and weight loss. Heart inflammation, with accompanying rapid heartbeat, murmurs, and enlargement, can lead to valve scarring, markedly shortening life. After recovery, survivors are prone to future attacks. Penicillin given when the initial infection is diagnosed can prevent it. Otherwise, salicylic acid derivatives or corticosteroids help the symptoms.

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Infectious disease with recurring fever, caused by several spirochetes of the genus Borrelia, transmitted by lice, ticks, and bedbugs. Onset is sudden, with high fever, which breaks within a week with profuse sweating. Symptoms return about a week later. There may be 2 to 10 relapses, usually decreasing in severity. Mortality usually ranges from 0 to 6percnt, up to 30percnt in rare epidemics. Central nervous system involvement causes various (usually mild) neurological symptoms. The first microscopic organisms clearly associated with serious human disease (1867–68), the spirochetes mutate repeatedly, changing their antigens so that the host's immunity no longer is effective, which produces the relapses. Antibiotics can be effective, but inadequate therapy may leave spirochetes alive in the brain, and they may reinvade the bloodstream.

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or childbed fever

Infection of the female reproductive system after childbirth or abortion, with fever over 100 °F (38 °C) in the first 10 days. The inner surface of the uterus is most often infected, but lacerations of any part of the genital tract can give bacteria (often Streptococcus pyogenes) access to the bloodstream and lymphatic system to cause septicemia, cellulitis (cellular inflammation), and pelvic or generalized peritonitis. Severity varies. Puerperal fever has become very rare in developed countries but is still seen after abortions performed in unhygienic surroundings.

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Seasonal sneezing, nasal congestion, and tearing and itching of the eyes caused by allergy to the pollen of certain plants. These plants are chiefly those pollinated by the wind (e.g., ragweed in North America, timothy grass in Britain). Antihistamines and corticosteroids may provide temporary relief, but the most effective long-range treatment is desensitization. Unless properly treated, about one-third of patients with hay fever develop asthma.

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or glandular fever

Common infection, caused by Epstein-Barr virus. It occurs most often at ages 10–35. Infected young children usually have little or no illness but become immune. Popularly called “the kissing disease,” it is spread mostly by oral contact with exchange of saliva. It usually lasts 7–14 days. The most common symptoms are malaise, sore throat, fever, and lymph-node enlargement. Liver involvement is usual but rarely severe. The spleen often enlarges and in rare cases ruptures fatally. Less frequent features include rash, pneumonia, encephalitis (sometimes fatal), meningitis, and peripheral neuritis. Relapse and second attacks are rare. Diagnosis may require blood analysis. There is no specific therapy.

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or pyrexia

Abnormally high body temperature or a disease characterized by it. It most often occurs with infection. Normal core body temperature, measured orally, does not exceed 99°F (37.2°C). Up to 105°F (40.6°C), fever causes weakness and is best treated with aspirin, acetaminophen, or other antipyretic drugs. At 108°F (42.2°C) or more, it can lead to convulsions and death. In treatment, it is important to know the underlying cause. Fever appears to be a defense against infectious disease, stimulating leukocytes and increasing antibody production and perhaps killing or inhibiting bacteria and viruses that live within a narrow temperature range.

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or breakbone fever or dandy fever

Infectious, disabling mosquito-borne fever. Other symptoms include extreme joint pain and stiffness, intense pain behind the eyes, a return of fever after brief pause, and a characteristic rash. Dengue is caused by a virus carried by mosquitoes of the genus Aedes, usually A. aegypti, which also carries yellow fever. There are four strains of virus; infection with one type does not confer immunity to the remaining three. Treatment focuses on relieving symptoms. Patients should be isolated during the first three days, when mosquitoes can pick up the disease from them. Prevention relies on mosquito control.

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Typhus-like disease first seen in the Rocky Mountain region, caused by the bacterium Rickettsia rickettsii (see rickettsia) and transmitted by various ticks. In severe cases the rash bleeds more and is especially prominent on the wrists and ankles. Central nervous system involvement causes restlessness, insomnia, and delirium. Prostration may progress to coma, with death possible in a week or more. Mortality increases with age. Recovery is slow but usually complete as visual disturbances, deafness, and mental confusion pass. Prompt antibiotic treatment hastens it and reduces mortality. Prevention depends on avoiding tick bites, by wearing long, light-coloured clothing and insect repellent and inspecting for ticks. A vaccine reduces the risk of infection somewhat and of death greatly.

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