The subtropical areas near the borders between Argentina, Brazil and Paraguay have recently witnessed an important increase in the number of yellow fever cases. We hereby provide some useful information regarding transmission, symptoms, treatments and prevention of this dangerous disease.

Scientists throughout the region have expressed their concerns regarding the increase in the number of cases of yellow fever reported in Brazil and Paraguay. This adds up to the fact that there has also been an important increase in the death rate of monkeys in wild populations that live in the Natural Reserves of Piñalito and Guirá Ogá, near Puerto Iguazú, in the province of Misiones, Argentina. The risks of yellow fever transmission in the region have also increased dramatically in urban areas, mostly due to changes in the socio-economic conditions of their populations, and to the fact that at this time of the year the climatic and environmental conditions are particularly favourable for the vector mosquito to spread the virus.

Recently Mundo Sano Foundation has been monitoring the presence of the vectors Aedes aegypti and A. albopictus in the Argentine province of Misiones. The former was already detected in the area during the month of February 2007 not only in wild areas near Puerto Iguazú, but also in some urban neighbourhoods of the city. This fact has made clear that some of the most important issues to be addressed in the future are to keep the levels of urban infestation as low as possible, and to detect potential new cases of yellow fever amongst the population in the early stages of the illness.

YELLOW FEVER Q&A

What is yellow fever?
Yellow fever is an acute infectious disease caused by a virus that belongs to the Flaviviridae family. The disease can persist for a period of up to 10 days, showing different levels of seriousness.

How is yellow fever transmitted?
Transmission of yellow fever occurs through mosquito bites, mostly individuals of Aedes aegypti and A. albopictus that carry the virus.

What are the symptoms of yellow fever?
Sudden high fever, general discomfort, loss of appetite, nausea, headache and body ache, shivers, and jaundice. Occasionally, spontaneous bleeding of mucosa and gums can also be observed.

What should I do if I feel any of these symptoms?
Immediate medical care should be sought

How should yellow fever be treated?
At present there is no specific treatment for yellow fever. Patients are advised to keep rest. Liquid reposition by intravenous methods is also suggested. Blood transfusions are recommended in cases of severe bleeding.

How can yellow fever be prevented?
Vaccination is the primary and most important method of prevention, providing a ten years protection period. Vaccination, however, is contraindicated in cases of pregnancy and for children under 9 months old. In urban areas, vector control of A. aegypti and A. albopictus mosquitoes is also strongly recommended.


Transmission cycle and risk in urban areas

So far two transmission cycles have been described for yellow fever: one cycle is known as the "sylvatic or forest cycle" which occurs between primates, and whose main vectors are mosquitoes from the genus Haemagogus and Sabethes. These mosquitoes feed on non-human primates infected with the virus. The infected mosquitoes then feed on humans travelling through or working in the forest, spreading in this way the virus. The second cycle is also known as the "urban cycle" in which the virus is transmitted from man to man by means of the mosquito vector A. aegypti.

The latter cycle can also feed from the former by means of humans that move from forest or rural areas into urban areas with presence of A. aegypti (a), or by means of mosquitoes that are capable of developing their full biological cycle either in forest or urban environments (b). These latter mosquitoes can be infected by the virus in the forest, and then transmit it to humans in the cities. In this sense, villages that are located near forests or endemic areas usually show a high epidemiological risk, mostly due to the fact that the presence of A. albopictus is higher in the interface of both environments.



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