Yellow Fever

Yellow fever is an infectious disease caused by a virus ^* and transmitted to humans by mosquitoes. It was given its name because of the jaundice ^* and high fever that accompany severe infections.

KEYWORDS

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Aedes aegypti

Epidemic

Mosquito

Vaccination

What Is Yellow Fever?

Once causing epidemics ^* in many parts of the world, including the United States, yellow fever now is confined almost entirely to tropical parts of Africa and South America. There it occurs in two forms, urban and sylvan.

Urban yellow fever is spread from person to person in densely populated areas by the bite of the Aedes aegypti (a-EE-deez ee-JIP-she) mosquito. Sylvan (forest) yellow fever occurs among humans and monkeys in sparsely populated jungles and rain forests, where it is spread by various mosquitoes other than A. aegypti. One person cannot catch yellow fever directly from another.

Eradication of the mosquito carrying the yellow fever virus from many heavily populated areas long ago has reduced the incidence of yellow fever greatly worldwide. Nonetheless, epidemics still break out occasionally in some African cities today. The disease is endemic ^* in forests and local populations of many tropical countries.

What Are the Symptoms of Yellow Fever?

The yellow fever virus attacks the central nervous system ^* and other organs, especially the liver, kidneys, and heart. Fever, headache, and bone pains develop suddenly 3 to 6 days after infection, and they often are accompanied by nosebleeds and stomach distress. Most cases are mild, and the individual recovers in 2 or 3 days.

^* virus (W-rus) is a tiny infectious agent that lacks an independent metabolism (me-TAB-o-lizm) and can only reproduce within the cells it infects.

^* jaundice (JAWN-dis) is a yellowing of the skin arising from the deposition of bile pigments; it occurs as a symptom of many liver and bile duct disorders.

^* epidemics (ep-i-DEM-iks) are outbreaks of diseases, in which the number of cases suddenly becomes far greater than usual.

^* endemic (en-DEM-ik) describes a disease that is present in a population or geographic area at all times,

^* central nervous system refers to the brain and the spinal cord, which coordinate the activity of the entire nervous system,

The U.S. and the World

The Rockefeller Commission

Yellow fever is endemic mostly in the Americas, especially in South American coastal regions. Just prior to the opening of the Panama Canal in 1914, Asian countries feared that yellow fever would be spread from America to the Eastern Hemisphere by means of newly established shipping routes.

In response to protest from countries like Japan, American medical experts testified before a commission that the most effective means of dealing with yellow fever would be through its worldwide eradication. Such an idea seemed feasible, as earlier programs of regional control had been successful.

The Rockefeller Yellow Fever Commission developed a plan to destroy centers where mosquitoes that carry yellow fever were most concentrated. Seemingly successful programs were carried out through the 1920s; however, by the 1930s, it increasingly became evident that eradication of yellow fever was not possible, and that immunization was necessary.

In 1928 the first yellow fever vaccine was prepared by the English physician Edward Hindle. Two more vaccines were developed by the bacteriologist (bak-teer-ee-OL-o-jist) MaxTheiler in 1937, for which he was awarded the Nobel Prize for medicine.

In severe cases, there is a brief period when symptoms subside. The fever then returns, and the heart rate is unusually slow. The skin turns yellow, and bleeding in the stomach causes so-called black vomit. These patients may recover, or they may become delirious ^* and go into a coma ^* leading to death.

The mortality rate in yellow fever is estimated to be about 10 percent on the average, but it is higher in severe illness. Patients who recover have a lifelong immunity ^* .

How Is Yellow Fever Diagnosed and Treated?

Severe cases of yellow fever can be diagnosed readily from the symptoms and can be confirmed with blood tests, which can detect the yellow fever virus and antibodies ^* .

There is no cure for yellow fever. Treatment consists mostly of complete bed rest and replacement of body fluids.

Immunization is effective. Just one injection of yellow fever vaccine ^* gives protection for 10 years or more. Vaccination (vak-si-NAY-shun) is essential in countries where the disease is prevalent, and for people planning to travel in those countries. From the public health standpoint, the key to prevention is mosquito control.

The Panama Canal

Yellow fever probably originated in Africa. The disease spread to western Europe and to the American colonies in the 1700s, and during the 1800s severe epidemics regularly broke out in the United States in port cities as far north as New York. It was also rampant in Latin America, taking many lives.

In the early 1900s, the American physician Walter Reed and his coworkers proved that yellow fever is transmitted by mosquitoes. William Gorgas, a U.S. Army physician, then instituted mosquito control measures that virtually eliminated the disease in Havana, Cuba. The successful completion of the Panama Canal in 1914 was due largely to the application of these measures in the canal area.

In 1937, Max Theiler, a South African physician, developed an effective vaccine for yellow fever.

^* delirious (dee-LEER-ee-us) refers to an acute mental syndrome characterized by confusion, disordered thinking, and halluci-nations (ha-loo-si-NAY-shunz).

^* coma (KO-ma) in an unconscious state, like a very deep sleep. A person in a coma cannot be woken up, and cannot move, see, speak, or hear.

^* immunity (i-MYOO-ni-tee) is the condition of being protected against an infectious disease.

^* antibodies (AN-ti-bod-eez) are proteins produced by the immune system to fight specific infections.

^* vaccine (vak-SEEN) is a preparation of killed or weakened germs, or of proteins made from such microbes, administered in order to prevent, lessen the severity of, or treat a disease.

Resources

Book

Wills, Christopher. Yellow Fever, Black Goddess: The Coevolution of People and Plagues. Pacific Palisades, CA: Perseus Press, 1997.

Organizations

The U.S. Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, N.E., Atlanta, GA 30333. The U.S. government authority for information about infectious and other diseases, the CDC posts information about yellow fever at its website.
http://www.cdc.gov/ncidod/dvbid/yellowf.htm

The World Health Organization (WHO), Avenue Appia 20, 1211 Geneva 27, Switzerland. This group's website posts a fact sheet about yellow fever.
http://www.who.int/emc/diseases/yellow_fever/index.html

Travel Health Online is a helpful website for travelers that posts information about yellow fever.
http://www.tripprep.com/index.html