Yellow Fever

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What is Yellow Fever?

Yellow fever is a disease caused by a virus that is transmitted by the bite of an infected mosquito.  It gets its name from the yellowing of the skin and eyes (jaundice) that occurs when the virus attacks the liver. Yellow fever can be prevented by a vaccine. 

Cause

A flavivirus, similar to West Nile and dengue fever viruses.

Risk to Travellers

Varies by season, destination, length of stay, and type of activities.

Low for most travellers, particularly those staying in highly developed major urban areas.

Greater for travellers who are:

  • visiting rural or jungle areas
  • staying for a long time
  • participating in outdoor activities such as camping, hiking, cycling or fieldwork

Severity            

Can range from asymptomatic to fatal.

Most people experience flu-like symptoms that disappear after three to four days.  About 15% of those who are infected then develop more serious symptoms, which can often lead to death. 

Prevention

For initial vaccine recipients, get vaccinated at least 10 days before you travel. This is a legal requirement for those countries requiring a yellow fever certificate (International Certificate of Vaccination).

Protect yourself from mosquito bites.

Treatment

There is no specific treatment for yellow fever.

Once symptoms develop, the only care is supportive.

Intensive supportive care may improve patient outcomes.

Symptoms

  • Can take three to six days to appear.
  • Usually include sudden onset of fever, headache, joint pain, loss of appetite, abdominal pain, vomiting and dehydration. Most patients recover after this stage.
  • In severe cases, the disease can lead to shock, internal bleeding, jaundice (yellowing of the skin and eyes) and organ failure. This occurs in about 15% of patients. The case-fatality rate for those who develop severe yellow fever disease is 15-50%.

Transmission

  • Yellow fever is spread through the bite of infected mosquitoes — mainly Aedes aegypti but other Aedes species in Africa and Haemagogus species in South America also play a role in transmission.
  • These mosquitoes can be domestic (they breed around houses), wild (they breed in the jungle), or semi-domestic types (they display a mixture of habits). Any region populated with these mosquitoes can potentially harbour the disease.
  • Non-human primates (e.g., monkeys) can also be infected with the yellow fever virus; this allows for the virus to remain present in rural or jungle areas without human hosts.
  • Yellow fever epidemics occur in urban areas when infected people carry the disease from rural or jungle areas into densely populated areas where there are mosquitoes capable of spreading the disease.

Where is Yellow Fever a Concern?

Yellow fever is endemic (always present) in many tropical areas of South America and Africa.

  • In South America, the countries considered to have the greatest risk of contracting yellow fever include Bolivia, Brazil, Colombia, Ecuador and Peru. Several Caribbean islands are at low risk for epidemics.
  • Countries at risk for yellow fever in Africa are typically situated on or around the equator.
  • Yellow fever is not endemic in Asia, however since both the mosquitoes and the non-human primates are present in different parts of Asia, there is potential for future epidemics.

A list of countries where yellow fever transmission occurs is available from the World Health Organization (WHO).

Recommendations

Consult a doctor, nurse or health care provider, or visit a travel health clinic preferably six weeks before you travel.

  1. Get vaccinated
    • It is recommended that you get the yellow fever vaccine before you travel if you are:
    • The single-dose vaccine against yellow fever is safe, effective and recommended for most people who are over nine months of age. 
    • The vaccine is generally not recommended for pregnant or breastfeeding women, children under the age of nine months, adults 60 years and older (especially those who have not previously received the vaccine) and people with weakened immune systems.
    • It takes 10 days before the vaccine takes effect so leaving vaccination to the last minute will leave you at risk. The vaccine provides immunity for 10 years or more. In Canada, the vaccine is available only at designated Yellow Fever Vaccination Centres.
  2. Protect yourself from mosquito bites , particularly two to three hours after dawn and during the early evening.

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