Yellow Fever

Yellow fever is an infectious disease caused by a virus that is transmitted to humans by mosquitoes.

What Is Yellow Fever?

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 urban cycle (left) involves transmission of the virus between humans and urban mosquitoes, primarily Aedes aegypti. The virus is usually brought to the urban setting by a human who was infected in the jungle or savanna.

The urban cycle (left) involves transmission of the virus between humans and urban mosquitoes, primarily Aedes aegypti. The virus is usually brought to the urban setting by a human who was infected in the jungle or savanna. The jungle (sylvatic) cycle (right) involves transmission of the virus between nonhuman primates (e.g., monkeys) and mosquito species found in the forest canopy. The virus is transmitted by mosquitoes from monkeys to humans when humans are visiting or working in the jungle.

The disease once caused epidemics *

Walter Reed and the U.S. Yellow Fever Commission

Walter Reed (1851–1902), an American military surgeon and head of the U.S. Army Yellow Fever Commission, is widely known as the man who conquered yellow fever by tracing its origin to a particular mosquito species.

Reed was born in Belroi, Virginia, the son of a Methodist minister. After attending private schools, Reed entered the University of Virginia, where he received his medical degree in 1869, after completing only two years. He then went to New York, where he received a second medical degree from the Bellevue Hospital Medical College in 1870. In June 1875, after working for the Board of Health of New York and Brooklyn, Reed was commissioned as an assistant surgeon in the U.S. Army with the rank of first lieutenant. Then followed 11 years of frontier garrison duty, further study at Johns Hopkins Hospital while on duty in Baltimore, and an assignment as professor of bacteriology and clinical microscopy at the newly organized Army Medical School in Washington in 1893.

When yellow fever made its appearance among U.S. troops in Havana, Cuba, in 1900, Reed was appointed head of the commission of army medical officers to investigate the cause and mode of transmission. After some months of fruitless work in searching for the cause of the disease, Reed and his associates decided to concentrate on determining the mode of transmission. Carlos Juan Finlay first advanced the theory that yellow fever was transmitted by mosquitoes (he blamed it on the Stegomyia fasciata, later known as the Aedes aegypti) and proved it by experiments, but physicians generally did not credit the possibility. Reed confirmed Finlay's findings by using human subjects. Reed and his associates argued that there was no alternative to experimentation with humans and that their results would justify the practice. Mosquitoes that had been fed on yellow fever–infected blood were applied to several of Reed's associates, including Dr. James Carroll, who developed the first experimental case of the disease.

There followed a series of controlled experiments with soldier volunteers. In all, 22 cases of experimental yellow fever were produced: 14 by mosquito bites, 6 by injections of blood, and 2 by injections of filtered blood serum. At the same time, in order to disprove the theory that the disease could be transmitted by mere physical contact, Dr. Robert P. Cook and a group of soldiers slept in a detached building with the clothing and bedding of yellow fever patients from the camp hospital. No cases of the illness resulted, and the theory was conclusively falsified.

The value of the commission's work quickly became evident. In 1900 there had been 1,400 cases of yellow fever in Havana; by 1902, after more than a year of mosquito eradication prompted by the report of Reed's commission, there was not a single case. Once its mode of transmission was known, there was no danger of yellow fever in any country with adequate control facilities.

Are There Different Kinds of Yellow Fever?

How Do People Know They Have Yellow Fever?

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.

How Do Doctors Diagnose and Treat Yellow Fever?

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.

How Can Yellow Fever Be Prevented?

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


Books and Articles

Busowski, Mary T. “Yellow Fever.” Medscape, June 26, 2015. (accessed November 4, 2015).

Garske, Tini, et al. “Yellow Fever in Africa: Estimating the Burden of Disease and Impact of Mass Vaccination from Outbreak and Serological Data.” PLoS Med 11, no. 5 (2014): e100163. (accessed November 4, 2015).


Government of Canada. “Yellow Fever.” Travel Health and Safety. (accessed November 4, 2015).

MedlinePlus. “Yellow Fever.” U.S. National Library of Medicine. (accessed November 4, 2015).

NHS Choices. “Yellow Fever.” National Health Service. (accessed November 4, 2015).


National Center for Emerging and Zoonotic Infectious Diseases. 1600 Clifton Rd., Atlanta, GA 30329-4027. Toll-free: 888-674-6854. Website: (accessed November 4, 2015).

World Health Organization. Avenue Appia 20, 1211 Geneva 27, Switzerland. Telephone: 41 22 791 21 11. Website: (accessed September 5, 2015).

* 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.

  This information is not a tool for self-diagnosis or a substitute for professional care.