Yellow fever is a disease carried by mosquitoes. Yellow fever is caused by a virus. The virus damages many body tissues, but especially the liver. As a result of this damage, the liver cannot function properly. Yellow bile pigments build up in the skin. These pigments make the skin look yellow, a condition called jaundice. The build-up of yellow pigments gives the disease its name. Today, yellow fever occurs only in tropical areas of Africa and South America. In the past, however, the disease was more widespread. It occurred in Europe, the Caribbean, Central America, and North America.
In the wild, yellow fever is transmitted in what is known as a jungle cycle of infection. The cycle involves monkeys and various species of mosquitoes. People may become infected when they live or work in jungle areas and are bitten by infected mosquitoes. Infected people may then take the virus to urban areas. Mosquitoes of the species Aedes aegypti transmit the virus from person to person in an urban cycle of infection. This mosquito species prefers urban environments. The urban cycle is uncommon in South America due to mosquito control measures. Today, urban yellow fever occurs only in Africa.
Symptoms
of yellow fever typically appear three to six days after a bite from an infected mosquito. Symptoms include a sudden fever, headache, muscle pain, backache, weakness, nausea, and vomiting. Most patients have only a mild case of the disease and quickly recover. During this time, however, they have the virus in their blood. They can spread the virus to mosquitoes, which can then transmit it to other people. Some patients experience a short period when symptoms disappear followed by a second phase of illness called the toxic phase. Symptoms of the toxic phase include high fever, vomiting, jaundice, bleeding, and coma. About 20 to 50 percent of these patients die within 10 days. Patients who recover are then immune to the disease.
Prevention.
Mosquito control measures have eliminated yellow fever in many urban areas of South America and Africa. Yellow fever can be prevented by a vaccine, called 17D. The vaccine was developed in 1937 by Max Theiler, a South African research physician. In 1951, Theiler was awarded the Nobel Prize in medicine for the development of this vaccine. Vaccination with 17D provides immunity from yellow fever for at least 10 years. The World Health Organization (WHO) recommends that people get an additional booster dose of the vaccine after 10 years.
Physicians do not recommend the vaccine for certain people. They include children under 9 months of age, pregnant women, and people with weakened immune systems. A small number of people have developed vaccine-associated neurotropic disease after receiving yellow fever vaccine. This serious disease affects the brain and can be fatal. Most cases have occurred among children under 6 months of age who received the vaccine.
History.
The conquest of yellow fever was one of the great achievements of modern medicine. In 1881, Carlos Finlay, a Cuban physician, suggested that a mosquito transmitted the disease. A United States Army physician, William Gorgas, developed mosquito control measures. His measures eliminated the disease as a major health menace in the Panama Canal Zone. Walter Reed, a U.S. Army doctor, proved that yellow fever was carried by a mosquito. Reed suggested that the cause was a microorganism. In 1927, three research physicians proved that the microorganism was a virus.
