Yellow fever is an infectious disease caused by a virus that is transmitted to humans by mosquitoes.
Yellow fever is a disease caused by yellow fever virus, a member of the Flavivirus (FLAY-vih-vy-rus) group of viruses. The disease gets its name because it often causes jaundice * , which tints the skin yellow, and a high fever. Yellow fever also can cause kidney failure and uncontrolled bleeding, or hemorrhaging (HEM-rij-ing). Many cases produce only mild illness, but severe cases of yellow fever can be fatal. Once someone has survived the disease, the person has lifetime immunity * against it.
Yellow fever afflicts both humans and monkeys and has been known since at least the 1600s. The disease is not spread by person-to-person contact. It is transmitted by several different species of mosquitoes; a person can contract yellow fever only from the bite of a mosquito that has bitten an infected person or monkey.
The disease once caused epidemics *
After an incubation period of three to six days, the yellow fever virus begins to produce symptoms. An early phase of disease occurs, which includes fever, headache, muscle aches, and vomiting. The infected person may have a slower heartbeat than that expected with a high fever. After a few days, most of the symptoms disappear. Many people recover from yellow fever at this point without complications. However, about 15 percent of patients develop a second, toxic phase of the disease, in which fever reappears and the disease becomes more severe. Inflammation * of the liver occurs, along with jaundice, stomach pains, and vomiting. The mouth, nose, eyes, and stomach can bleed uncontrollably, with blood present in vomited material and bowel movements. The kidneys may begin to fail, and patients may go into a coma.
Early stages of yellow fever can be easily confused with other diseases such as malaria (a disease spread to humans by the bite of an infected mosquito); typhoid fever (an infection from the bacterium Salmonella typhi that causes fever, headache, confustion, and muscle aches), and other hemorrhagic (heh-muh-RAH-jik) fevers; and types of viral hepatitis (an inflammation of the liver). Blood tests can detect whether a patient's body has produced yellow fever antibodies * to fight the infection. Doctors also will take a travel history to see if a patient has recently visited a country where yellow fever occurs.
No specific treatment exists for yellow fever. Care is geared toward treating complications of the disease. In serious cases, intensive care in the hospital usually is needed. Patients may be given fluids to prevent dehydration * , and blood transfusions * may be necessary if bleeding is severe.
Most people who contract yellow fever recover from the early phase of the disease within a week; those who progress to the toxic phase may take several weeks or longer to recover. About half of those who develop toxic phase symptoms die within two weeks; the other half may recover without significant long-term problems.
Vaccination * against yellow fever is the single most important prevention measure, and it is a must for people traveling to countries where the disease is common. Most countries in which yellow fever occurs require a certificate proving that travelers have been vaccinated before they are allowed into the country. One dose of vaccine provides at least 10 years of immunity.
Doctors recommend that infants under six months of age, pregnant women, people allergic to eggs (eggs are used in producing the vaccine), and people with a weakened immune system * (such as people who have AIDS * or certain cancers) not receive the vaccine; these people are advised to delay visits to countries where yellow fever is endemic * .
Avoiding mosquito bites when traveling abroad reduces the risk of contracting yellow fever. To help prevent infection, experts suggest that travelers:
See also Dengue Fever • Hepatitis • Malaria • Travel-Related Infections: Overview • Vaccines and Immunization • West Nile Fever
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* jaundice (JAWN-dis) is a yellowing of the skin, and sometimes the whites of the eyes, caused by a buildup in the body of bilirubin, a chemical produced in and released by the liver. An increase in bilirubin may indicate disease of the liver or certain blood disorders.
* immunity (ih-MYOON-uh-tee) is the condition of being protected against an infectious disease. Immunity often develops after a germ has entered the body. One type of immunity occurs when the body makes special protein molecules called antibodies to fight the disease-causing germ. The next time that germ enters the body, the antibodies quickly attack it, usually preventing the germ from causing disease.
* epidemics (eh-pih-DEH-miks) are outbreaks of diseases, especially infectious diseases, in which the number of cases suddenly becomes far greater than usual. Usually, epidemics that involve worldwide outbreaks are called pandemics.
* inflammation (in-fla-MAY-shun) is the body's reaction to irritation, infection, or injury that often involves swelling, pain, redness, and warmth.
* antibodies (AN-tih-bah-deez) are protein molecules produced by the body's immune system to help fight specific infections caused by microorganisms, such as bacteria and viruses.
* dehydration (dee-hi-DRAY-shun) is a condition in which the body is depleted of water, usually caused by excessive and unreplaced loss of body fluids, such as through sweating, vomiting, or diarrhea.
* transfusions (trans-FYOO-zhunz) are procedures in which blood or certain parts of blood, such as specific cells, are given to a person who needs them due to illness or blood loss.
* vaccination (vak-sih-NAY-shun), also called immunization, is giving, usually by an injection, a preparation of killed or weakened germs, or a part of a germ or product it produces, to prevent or lessen the severity of the disease caused by that germ.
* immune system (im-YOON SIStem) is the system of the body composed of specialized cells and the substances they produce that helps protect the body against disease-causing germs.
* AIDS, or acquired immunodeficiency (ih-myoo-no-dih-FIH-shensee) syndrome, is an infection that severely weakens the immune system; it is caused by the human immunodeficiency virus (HIV).
* endemic (en-DEH-mik) describes a disease or condition that is present in a population or geographic area at all times.