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Yellow Fever

Yellow fever is a reportable disease in Oklahoma. The disease is caused by the yellow fever virus, which belongs to the flavivirus group. Yellow fever is a viral disease that has caused large epidemics in Africa and the Americas. Infection causes a wide spectrum of disease, from mild symptoms to severe illness and death. The "yellow" in the name is explained by the jaundice that affects some patients. Yellow fever occurs in tropical regions of Africa and in parts of South America. The last epidemic of yellow fever in North America occurred in New Orleans in 1905.

Yellow fever is transmitted by the bite of infected mosquitoes. Humans and monkeys are the principal mammals infected. The virus is carried from one animal to another (horizontal transmission) by a biting mosquito (the vector). The mosquito can also pass the virus via infected eggs to its offspring (vertical transmission). The eggs produced are resistant to drying and lie dormant through dry conditions, hatching when the rainy season begins. Therefore, the mosquito is the true reservoir of the virus, ensuring transmission from one year to the next. 
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Individuals with yellow fever may be viremic (have virus in their blood) for three to six days before demonstrating symptoms. Initial symptoms include fever and chills, severe headache, back pain, general muscle aches, nausea, fatigue, and weakness. This phase may be followed by a short period of symptom remission.

The toxic phase develops as the fever returns, with clinical symptoms including high fever, headache, back pain, nausea, vomiting, abdominal pain, and fatigue.  Symptoms of bleeding include black vomit, nose bleed, gum bleeding, and purple pin-point spots (bruising).

In the late stages of disease, patients can develop hypotension, shock, kidney and heat complications. Confusion, seizures, and coma can also occur. When epidemics occur in unvaccinated populations, death rates range from 15% to more than 50%.  Symptoms of weakness and fatigue may last several months in people who recover. Those who recover from yellow fever generally have lasting immunity against subsequent infection.

How to prevent becoming infected with yellow fever virus:

  • Yellow fever can be prevented by vaccination. Travelers should get vaccinated for yellow fever before visiting areas where yellow fever occurs. Individuals are recommended to consult with their primary care physician or an international travel clinic at least three months prior to travel.
  • Avoid mosquito bites when traveling in tropical areas. Mosquitoes that spread yellow fever usually bite during the day, especially at dusk and dawn.
  • For additional information on disease prevention visit:

                  Mosquitoborne Disease Prevention Tips (148k.pdf)
                  Insect Repellent Fact Sheet (120k.pdf)

Internal Yellow Fever Resources:


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