Yellow Fever

What is Yellow Fever?

Yellow fever is a serious infectious disease that varies in the severity of illness. It is caused by the yellow fever virus.  There are three types of yellow fever.  One involves mosquitoes and non-human primates (monkeys) and is called jungle yellow fever since it occurs in forested rural areas.  An intermediate type involves humans, primates and various types of mosquitoes in savannah regions of Africa.  The third type is called urban yellow fever and involves humans and mosquitoes that are adapted to urban areas. In all three types, infected mosquitoes are the agents that transmit the disease to humans.

It is difficult to assess the risk of contracting yellow fever in the traveller since it depends on many different factors such as the traveller's destination, the season, the work and recreational activities, as well as the local activity of the virus.

How do you get Yellow Fever?

Yellow fever is transmitted to humans through the bite of an infected mosquito.

Susceptibility and Resistance

Any unvaccinated person is susceptible.

Recovery from yellow fever is followed by lasting life-long immunity. Immunity in nursing infants born to immune mothers may persist for up to 6 months. In natural infections, antibodies appear in the blood within the first week.  Yellow fever vaccination provides immunity for 10 years or more.

Incubation Period

The incubation period for Yellow Fever is 3-6 days.

What are the Symptoms?

Yellow fever is usually characterized by sudden onset of fever, chills, headache, backache, generalized muscle pain, prostration, nausea and vomiting. Jaundice (yellow skin) can occur early in the disease and progressively worsens later (20 to 50 percent of jaundiced cases are fatal). Most of the illness goes away following the early stage. Some cases progress, after a brief remission of hours to a day, to a stage that includes haemorrhagic symptoms including nose bleeds, bleeding from the gums, vomiting blood, black excrement, and liver and kidney failure. Around 5 percent of infected local populations will die, but that rate can reach 20 to 40 percent in individual outbreaks.

Preventative Measures

Yellow fever can be prevented by vaccination. A vaccination certificate is required for travel to certain countries. This certificate is also required if the traveller is going to or staying in a region where yellow fever occurs.

Avoiding mosquito bites will also reduce the risk of exposure to yellow fever.


Other than treatment of the symptoms, there is no specific treatment for yellow fever.


Where Does It Commonly Occur?

Jungle yellow fever occurs in Africa in the areas extending from the Sahara Desert south through northern Angola, Zaire,Nigeria and Tanzania. Recently, cases have been reported from Cameroon, Democratic Republic of the Congo, Guinea, and Senegal.

In forested areas of tropical Latin America, cases of the intermediate type of yellow fever have been reported from Bolivia, Brasil, Colombia, Ecuador, Peru, and Venezuela. There is no evidence that urban yellow fever has occurred in the Americas since 1942.

There is no evidence that yellow fever has ever been present in Asia or the easternmost coast of Africa.