Yellow fever is a viral disease that was first described in the mid-sixteenth century in Yucatan, Mexico. It is caused by the amaril virus, an arbovirus (a virus transmitted by an insect vector) isolated in 1927, simultaneously in Ghana and at the Institut Pasteur in Dakar, Senegal. The disease is currently endemic in Africa and has reemerged in South America. Some serious forms can be fatal. However, there is a safe, effective vaccine. A booster is recommended every ten years.
Symptoms and treatment
There is no specific treatment for yellow fever. Rest, drugs to lower temperature and relieve vomiting and pain, along with rehydration therapy, are the only methods of treatment for this disease.
Large-scale epidemics affected tropical America in the 17th, 18th and 19th centuries, and it became "the most dreaded disease in the Americas". Today, the disease is rife in the intertropical regions of America and Africa. For reasons unexplained, it has never spread to Asia.
The American continent
The spread of mosquito vectors
Different mosquito species – Aedes in Africa and Haemagogus janthinomys in South America – transmit the amaril virus to monkeys. In contrast to African monkeys, New World monkeys are very susceptible to infection, and show a high case fatality rate. The virus persists in mosquito-monkey-mosquito cycles – sylvatic forest cycles that do not naturally include humans. Yellow fever is a zoonosis, in all probability dating from ancient times, which was transmitted to humans when they ventured into tropical forests.
The mosquito responsible for urban epidemics is Aedes aegypti. This mosquito is also the vector for dengue, another arbovirus that is spreading rapidly throughout the world. Global warming may accelerate the introduction of mosquitoes that can transmit these diseases into the northern hemisphere, where international trade already provides opportunities for the disease to spread.
In 1937 a second vaccine (strain 17D), prepared from the attenuated virus, was developed at the Rockefeller Institute in the USA and rendered thermostable by a team at the Institut Pasteur in Paris. Its effectiveness and safety have progressively been improved, and make it one of the best viral vaccines currently available. This vaccine is now mainly produced at the Institut Pasteur in Dakar. The laboratory is approved by the World Health Organization to supply the yellow fever vaccine to Expanded Programs on Immunization in Africa. There are other manufacturers in Europe and America.
International regulations recommend yellow fever vaccinations (in a single injection) every ten years.
Yellow fever vaccination is the only mandatory vaccination for travelers to the endemic intertropical regions of Africa and South America.
At the Institut Pasteur
The Flavivirus-Host Molecular Interactions Unit is working to improve understanding of the molecular basis of yellow fever virus attenuation in the 17D vaccine strain, which is still in use today. The Dendritic Cell Immunobiology and Structural Virology units study the yellow fever virus from the angles of the pathophysiology of the viral infection and the structural biology of the virus.
The virus is also the subject of research work within the Institut Pasteur International Network, and in particular the Institut Pasteur in Dakar, Senegal.