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Yellow fever is found only in parts of Central and South America and Sub-saharan Africa.
The cause is a virus that is spread through the bite of an infected Aedes aegypti mosquito which predominantly bites during daylight hours. It exists in three transmission cycles; Jungle, Urban and Intermediate yellow fever.
Jungle yellow fever – is transmitted among non-human hosts (mainly monkeys) by forest mosquitoes. Humans can become infected when they spend time in the forest and can become the source of urban yellow fever outbreaks.
Urban yellow fever – is spread to urban areas by mosquitoes, mainly Aedes aegypti, that have bitten monkeys or humans infected with yellow fever. Urban yellow fever can occur in populated areas in close proximity to forests where infected monkeys and the mosquitoes can be found.
Both jungle and urban cases occur in Africa (especially west Africa). Urban cases are rare in the Americas.
Intermediate yellow fever – occurs only in Africa in humid savannah regions where mosquitoes infected both monkeys and humans causing localised outbreaks.
The incubation period is usually short, 3-6 days. Symptoms of the disease include sudden onset of fever, backache, generalised muscle pain, nausea and vomiting. Jaundice can also be seen early in the disease and this intensifies as the disease progresses. Infection with yellow fever results in lifelong natural immunity in individuals who survive. Up to 60% of those infected with yellow fever will die from the disease.
There is no specific treatment for yellow fever virus.
Yellow fever vaccination is carried out for two different purposes:
- To prevent the international spread of the disease by protecting countries from the risk of importing or spreading yellow fever virus. These are mandatory requirements established by the country. The countries that require proof of vaccination are those where the disease may or may not occur and where the mosquito and potential non-human primate hosts of yellow fever are present. Any importation of the virus by an infected traveller could result in its propagation and establishment, leading to a permanent risk of infection for the human population. Proof of vaccination is often required for travellers coming from countries with risk of yellow fever transmission (including, sometimes, for travellers transiting through such countries).
- Some countries require proof of vaccination from all travellers.
- To protect individual travellers who may be exposed to yellow fever infection. As yellow fever is frequently fatal for those who have not been vaccinated, vaccination is recommended for all travellers (with a few exceptions) visiting areas where there is a risk of yellow fever transmission. An individual risk assessment is indicated for all travellers.
Areas with Risk of Yellow Fever Transmission
The following maps show the approximate areas which have a risk of yellow fever transmission. Below each map is a list of these countries.
|Burkina Faso||Sierra Leone|
|Central African Republic||Togo|
|Congo, Republic of|
|Democratic Republic of Congo||In the Americas|
|Niger||Trinidad and Tobago (Trinidad only)|
Some countries do not exactly follow these World Health Organisation guidelines:
India does not consider Argentina and Mauritania as areas with risk of yellow fever transmission. When a case of yellow fever is reported from any country, that country is regarded by the Government of India as a country with risk of yellow fever and is added to the list.