Disease Fact Sheet - Yellow Fever

Updated: January 2008

Yellow fever is a vaccine-preventable illness caused by the bite of an infected mosquito. Symptoms can range from flu-like symptoms to gastrointestinal bleeding, organ failure and death. The disease gets its name from the yellowing of the skin and eyes (jaundice) that occurs when the virus attacks a patient’s liver. The death rate from yellow fever can be as high as 30 per cent.

Transmission

Yellow fever is transmitted to humans through daytime-biting mosquitoes—mainly the Aedes aegypti and Haemagogus species—that are infected with the yellow fever virus. In the jungle or tropical rainforest, these mosquitoes feed on monkeys that are infected with the disease, and then bite humans working or traveling within the forest.

Occasionally, infected travelers from rural areas introduce the virus to cities, where the dense population makes it easy for mosquitoes to carry the disease from person-to-person. This urban cycle of transmission can cause large and explosive yellow fever epidemics.

Geographic distribution

Yellow fever is constantly present, or endemic, in many tropical areas of South America and Africa. On occasion, the number of yellow fever cases can increase dramatically to the epidemic level (greater number of cases than usually expected within a specific given time). For the most part, yellow fever transmission is restricted to rural and jungle areas.  Small-scale rural epidemics are however becoming increasingly common in the humid and semi-humid savannahs of Africa.

For a list of countries with risk of yellow fever transmission, visit the World Health Organization (WHO) website: http://www.who.int/ith/Annex1_ITH%202008.pdf and http://www.who.int/ith/countries/en/index.html

Symptoms

Symptoms of yellow fever take three to six days to appear after being infected and include sudden onset of fever, headache, joint pain, loss of appetite, abdominal pain and vomiting. In severe cases, yellow fever can lead to shock, bleeding, organ failure, jaundice—yellowing of skin and eyes—and death.

Treatment

There is no specific treatment for yellow fever, so prevention of the disease through vaccination is the main form of protection. Once symptoms develop, the only care is supportive and despite advanced interventions, people may still die. The overall death rate during a single outbreak may reach as high as 30 per cent.

Vaccine

The single-dose vaccine against yellow fever is safe, effective and recommended for individuals nine months of age and older. The vaccine becomes protective 10 days after vaccination, or immediately after revaccination.  It provides immunity to a vaccinated individual for 10 years or more.

In Canada, the vaccination is available at designated Yellow Fever Vaccination Centres.  Individuals who receive the yellow fever vaccine are provided with an International Certificate of Vaccination or Prophylaxis as proof that they have been vaccinated against yellow fever. Some destinations require travelers to present this certificate before they are allowed to enter the country. (see International Health Regulations below).

Depending on their travel itinerary, the yellow fever vaccine may not be recommended for the following groups:

• pregnant and nursing mothers;
• people with depressed immune systems (e.g. from chemotherapy, HIV or steroid use);
• adults older than 60;
• children younger than nine months;
• people with a history of thymic disorders; and
• those with a severe allergy to eggs or chicken protein.

Travelers, who fit within one of these categories and are planning to visit a country where yellow fever is known to occur, are encouraged to visit a designated Yellow Fever Vaccination Centre for a personal risk assessment, and, if necessary, documentation from a health care professional explaining why they cannot receive the yellow fever vaccine. Travelers should be aware that this documentation will not guarantee them entry into a country where a certificate of vaccination is required. In some cases, unvaccinated individuals may have to wait in quarantine for up to six days before being allowed to enter a country requiring yellow fever vaccination.

International Health Regulations

Under the International Health Regulations, an International Certificate of Vaccination or Prophylaxis may be required at foreign border crossings. Some countries require all arriving travelers to show proof of yellow fever vaccination, while other countries require proof of vaccination only of travelers arriving or in transit from countries where yellow fever occurs.  Many countries that do not have yellow fever within their boarders may have all the right conditions (mosquitoes and primates) for an outbreak to occur. These countries may require proof of vaccination to prevent the spread of yellow fever.

The International Certificate of Vaccination or Prophylaxis is valid starting 10 days after the date of vaccination, or immediately after revaccination if the vaccine was given within 10 years of the previous yellow fever vaccination.  The certificate expires 10 years from the start date of validity.

For specific country requirements regarding yellow fever vaccination, visit the World Health Organization (WHO) website: http://www.who.int/ith/countries/en/index.html

Prevention & personal precautions

Vaccination is the single most important measure for preventing yellow fever. Mosquito-control precautions will decrease the risk of exposure to the yellow fever virus.

Vaccination
The Public Health Agency of Canada strongly recommends that travelers go to a travel health clinic or see their doctor at least six to eight weeks before departure to determine their risk of exposure to yellow fever, the risks and benefits of vaccination, and their need for official internationally accepted proof of vaccination as determined by their travel itinerary.

Mosquito-control precautions
Taking the following personal precautions may reduce the risk of exposure to day-time biting mosquitoes:

• when indoors, remain in well-screened or completely enclosed, air-conditioned areas;
• wear light-colored clothing with full-length pant legs and sleeves; and
• use mosquito netting treated with insecticide (especially to protect babies under six months while in playpens, cribs or strollers; and,
• use insect repellent on exposed skin.
1. do not apply to cuts, abrasions or irritated skin
2. do not spray directly on the face and wash hands after application to avoid contact with lips and eyes
3. DEET and sunscreen combination products are not generally recommended.  If application of both is required, apply the sunscreen first and let it soak into the skin for about 20 minutes before applying DEET.

For more detailed information on protecting yourself and your family against mosquito bites, refer to Statement on Personal Protective Measures to Prevent Arthropod Bites.

Know before you go!

Infectious diseases not necessarily common in Canada can occur and may even be widespread in other countries. Standards of hygiene and medical care may differ from those at home. Before departure, you should learn about the health conditions in the country or countries you plan to visit, your own risk of disease and the steps you can take to prevent illness.

The risk is yours
Your risk of acquiring a disease depends on several factors. They include: your age, gender, immunization status and current state of health; your itinerary, duration and style of travel (e.g., first class, adventure) and anticipated travel activities (e.g., animal contact, insect exposure, bathing in  fresh water, sexual contact); as well as the local disease situation.

Risk assessment consultation
The Public Health Agency of Canada strongly recommends that your travel plans include contacting a travel health clinic or your doctor six to eight weeks before departure. You’ll learn about health issues – ranging from minor inconveniences to serious illnesses – specifically related to your own health, destination and intended activities.  Based on such factors, a health care provider can determine your need for immunizations, preventive medications and precautions you should take to avoid illness and injury.

Some things to think about...

While yellow fever is rare in travelers, some unvaccinated travelers have died from this disease. Serious delays–and serious health risks–can result if a traveler arrives in some countries without official proof of vaccination. Remember: the International Certificate of Vaccination or Prophylaxis isvalid starting 10 days after the date of vaccination, or immediately after revaccination if the vaccine was given within 10 years of the previous yellow fever vaccination.  The certificate expires 10 years from the start date of validity.

For more information...

• For more information about yellow fever, visit the World Health Organization’s website.
• Visit the general information about other immunizations recommended for travel outside of Canada.
• For more information on how to prevent mosquito bites, please read the Statement on  Personal Protective Measures to Prevent Anthropod Bites.
• For more, Know before you go! information.