Yellow Fever

(This information is not intended to be a substitute for the advice of a doctor or a recommendation for any particular treatment plan. Like any printed material, it may become out of date over time. It is important that you rely on the advice of a doctor for your specific condition.)

Yellow fever is a viral infection transmitted by mosquitoes, Aedes and Haemagogus spp.  It should be noted that the mosquito vectors of yellow fever bite mostly during daylight hours. It cannot be spread person to person by direct contact. If a person is bitten by an infected mosquito, symptoms usually develop 3 - 6 days later. Humans infected with this virus experience the highest levels of viremia and can transmit the virus to mosquitoes shortly before onset of fever and for the first 3–5 days of illness.

This disease is common in tropical South America and in sub-Saharan Africa (between 15º southern - 15º northern latitude). Yellow fever virus transmission in rural West Africa is seasonal, with an elevated risk during the end of the rainy season and the beginning of the dry season (usually July–October). However, yellow fever virus may be episodically transmitted by A. aegypti even during the dry season in both rural and densely settled urban areas. The risk for infection in South America is highest during the rainy season (January–May, with a peak incidence in February and March).

Yellow fever has three stages:
• Early stage: Headache, muscle and joint aches, fever, flushing, loss of appetite, vomiting, and jaundice are common. After approximately 3 - 4 days, often symptoms go away briefly (remission).
• Period of remission: After 3 - 4 days, fever and other symptoms go away. Most people will recover at this stage, but others may move onto the third, most dangerous stage (intoxication stage) within 24 hours.
• Period of intoxication: Multi-organ dysfunction occurs. This may include heart, liver, and kidney failure, bleeding disorders, hemorrhage, and brain dysfunction including delirium, seizures, coma, shock, and death.

• Arrhythmias, heart dysfunction
• Bleeding (may progress to hemorrhage)
• Coma
• Decreased urination
• Delirium
• Fever
• Headache
• Jaundice
• Muscle aches (myalgia)
• Red eyes, face, tongue
• Seizures
• Vomiting
• Vomiting blood

Yellow fever varies in severity. Severe infections with internal bleeding and fever (hemorrhagic fever) are deadly in up to half of cases. A person with advanced yellow fever may show signs of liver failure, renal failure, and shock. There is no specific treatment for yellow fever. Treatment for symptoms can include:
• Blood products for severe bleeding
• Dialysis for kidney failure
• Fluids through a vein (intravenous fluids)

If you will be traveling to an area where yellow fever is common:
• Sleep in screened housing
• Use mosquito repellents
• Wear clothing that fully covers your body

There is an effective vaccine against yellow fever. Ask your doctor at least 10 - 14 days before traveling if you should be vaccinated against yellow fever. Yellow fever vaccine is a live, weakened virus. It is given as a single shot. For people who remain at risk, a booster dose is recommended every 10 years. Yellow fever vaccine may be given at the same time as most other vaccines. After getting the vaccine, you should be given a stamped and signed “International Certificate of Vaccination or Prophylaxis” (yellow card). This certificate becomes valid 10 days after vaccination and is good for 10 years.

(Source:  WHO, U.S. Centers for Disease Control and Prevention & U.S. National Library of Medicine - National Institute of Health)