Yellow fever is a serious viral illness with no cure. It is contracted through the bite of female mosquitoes found in areas in the South American rainforest, and throughout Africa. The mosquitoes pick up the virus when they bite a monkey or person who has it, then pass it by biting and infecting someone else.
In South America, the disease is usually only contracted in dense rain forests where monkeys are present, so it is sometimes called jungle yellow fever. People are most at risk for getting a bite from an infected mosquito during the day, and everyone going into jungle areas of South America are warned to wear insect repellent and spray their sleeping quarters.
Yellow fever contracted in Africa is usually passed from person to person via mosquito bite and is called urban yellow fever. Occasional outbreaks occur in various parts of the continent, and people are just as likely to become infected in a city or town as in jungle areas. Standard precautions should be taken to avoid getting bitten by a mosquito and infected. In particular, people should be wary of bites during the day, use insect repellent with DEET, and spray beds, bed nets, and clothing with insecticide.
In the past, this disease caused great problems in other areas of the world. Epidemics during the Spanish American War, and particularly the epidemic in Philadelphia in the 19th century, killed thousands of people. Early in the 20th century, scientists discovered the cause of yellow fever, and soon afterward, a vaccine was developed that has essentially eradicated the disease in the US and other parts of the world. Vaccines are less available to people in poorer areas. Thus parts of Africa and South America are prime targets for contracting the disease because people do not have the vaccine available.
Anyone traveling to an area where yellow fever is a problem should receive a vaccination that protects the person for up to ten years. People traveling from areas where the disease is found may also need to be cleared of being contagious with the disease, and may require a vaccination before they are admitted to countries free of the virus to avoid spreading it.