Yellow fever

Yellow fever is an infectious disease caused by the yellow fever virus. The disease is only present in tropical regions of Africa and South America. The virus is transmitted to humans by the yellow fever mosquito (Aedes aegypti), by other mosquitoes of the genus Aedes and by mosquitoes of the genus Haemagogus. Mosquitoes can transmit the virus to humans after themselves having been infected by a person or a monkey


Mosquitoes can transmit the yellow fever virus to humans after themselves having been infected by a viraemic person or monkey. Infection through blood transfusion, organ transplant, during pregnancy or breastfeeding is also possible. 


  • About 1 in 10 people infected become ill. Symptoms can vary from a mild flu-like illness to a serious infection that can be fatal.
  • After an incubation period of 2 to 9 days, the first symptoms appear, such a high fever, headaches and muscle pain. 
  • Most patients recover after 3 or 4 days. However, around 15-25% of them fall ill again after a short recovery period, with severe symptoms, such as jaundice, bleeding and a state of shock. 
  • Young children are more susceptible to severe forms of yellow fever (affecting the brain). Among people, who develop jaundice, the mortality rate is high, i.e. up to half of patients. 

Diagnosis, treatment and prevention

  • If the doctor suspects yellow fever, the diagnosis can be made by way of a blood test or lumbar puncture (in the case of severe illness). Depending on the stage of the disease, different tests can be used, such as a PCR test and serology.  
  • There is no specific treatment for yellow fever, only symptomatic treatment.
  • There is a very effective vaccine against yellow fever. In some countries, vaccination is mandatory for all travellers. Prevention is also done by avoiding mosquito bites. 

Sciensano is responsible for the epidemiological surveillance of yellow fever in humans in Belgium. As well as the monitoring of exotic mosquitoes of the genus Aedes (through the MEMO+ project).

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