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Medical Author:

Steven Doerr, MD

Steven Doerr, MD

Steven Doerr, MD, is a U.S. board-certified Emergency Medicine Physician. Dr. Doerr received his undergraduate degree in Spanish from the University of Colorado at Boulder. He graduated with his Medical Degree from the University Of Colorado Health Sciences Center in Denver, Colorado in 1998 and completed his residency training in Emergency Medicine from Denver Health Medical Center in Denver, Colorado in 2002, where he also served as Chief Resident.

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Medical Editor:

Mary D. Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP

Mary D. Nettleman, MD, MS, MACP is the Chair of the Department of Medicine at Michigan State University. She is a graduate of Vanderbilt Medical School, and completed her residency in Internal Medicine and a fellowship in Infectious Diseases at Indiana University.

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In this Article

• What is yellow fever? What is the history of yellow fever?
• What causes yellow fever?
• How is yellow fever transmitted?
• What areas are high-risk for contracting yellow fever?
• What is the incubation period for yellow fever?
• What are yellow fever symptoms and signs?
• How is yellow fever diagnosed?
• What is the treatment for yellow fever?
• What is the prognosis for people with yellow fever?
• Can yellow fever be prevented?
• Where can people get more information on yellow fever?
• Yellow Fever At A Glance
• Find a local Doctor in your town
• Yellow Fever Index

Yellow fever is caused by a virus. The yellow fever virus is a single-stranded RNA virus that belongs to the Flavivirus genus. After transmission of the virus occurs, it replicates in regional lymph nodes and subsequently spreads via the bloodstream. This widespread dissemination can affect the bone marrow, spleen, lymph nodes, kidneys, and liver, in addition to other organs. Tissue damage to the liver, for example, can lead to jaundice and disrupt the body's blood-clotting mechanism, leading to the hemorrhagic complications sometimes seen with yellow fever.

This picture shows multiple virions of the yellow fever virus. Source: CDC

Yellow fever is transmitted to humans by the bite of infected mosquitoes. Various species of Aedes and Haemagogus mosquitoes serve as vectors and are responsible for the transmission to human and nonhuman primates, which serve as reservoirs for the disease. Three transmission cycles for yellow fever have been identified.

• Sylvatic (jungle) cycle: In tropical rain forests, infected monkeys pass the virus to mosquitoes that feed on them. These infected mosquitoes then bite humans who enter the rain forest for occupational (for example, loggers) or recreational activities.



• Intermediate (savannah) cycle: In humid or semi-humid regions of Africa, mosquitoes that breed around households and in the wild (semi-domestic mosquitoes) infect both humans and monkeys. The virus can be transmitted from monkeys to humans, or from human to human by the mosquitoes. This is the most common type of outbreak in Africa.



• Urban cycle: When infected humans introduce the virus into urban areas with large numbers of unvaccinated individuals, infected mosquitoes (Aedes aegypti) transmit the disease from human to human. This form of transmission can lead to large epidemics.

This picture shows a female Aedes aegypti mosquito. Source: CDC