Yellow Fever (cont.)

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What causes yellow fever?

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

How is yellow fever transmitted?

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.
This picture shows a female Aedes aegypti mosquito. Source: CDC
Medically Reviewed by a Doctor on 1/16/2014

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