Pathogen and transmission
Yellow fever is an infectious disease caused by a virus which is spread by mosquitoes of the Aedes and Haemagogus genera. The mosquitoes can acquire the virus by biting an infected person or animal (bird or ape) and can then pass it on to humans.
Pathology
Three to six days after virus infection, the individual will experience a sudden high fever, chills, headache and joint pains, nausea and vomiting. These symptoms will persist for three to four days. In mild cases, the illness will then be over. In some 15 per cent of cases, however, after one or two days of being symptom-free, the individual will experience a renewed fever. This will be accompanied by stomach pains, a swelling of the liver, jaundice, kidney failure and bleeding of the skin, the mucus membranes and the gastrointestinal tract. Between 20 and over 50 per cent of such severe cases are fatal. Travellers and immigrants to yellow fever regions are more likely to develop the severe form of the disease than persons who are native to the regions concerned.
Distribution and frequency of occurrence
The virus is found in tropical areas of Africa and of Central and South America. In Switzerland, the disease has only been diagnosed once in past years, in a person who had returned from travel.
Prevention
A very effective yellow fever vaccine is available. The vaccine provides protection from ten days after vaccination and, unless the recipient has an immunodeficiency, will remain effective for life. Yellow fever vaccinations can only be administered by a doctor who is officially authorised to do so or at a medical centre with the same official authorisation.
Some countries have stricter immigration requirements, however, regarding yellow fever protection: they may, for instance, require that such vaccination is renewed every ten years, and demand documentary proof of such current vaccination protection. Needless to say, all such immigration provisions must be duly observed. Thus, it is very important to clarify any such requirements in good time in advance of any travel to the regions concerned.
For further information on the global distribution of yellow fever and ways and means to avoid yellow fever virus infection, consult your GP or a doctor specialising in travel medicine (see also the links below).