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Pathology => Human Diseases => Yellow Fever
Yellow Fever
INTRODUCTION
Yellow Fever, noncontagious, infectious disease, caused by a virus, and characterized in severe cases by high fever and jaundice. Originally yellow fever was believed to be exclusively a disease of humans, but research has revealed that it also affects monkeys and other animals. It is believed that diseased monkeys of Africa and tropical America are the primary source of infection and that carrier mosquitoes transmit the infection to humans. This type of the disease, which occurs only sporadically in human beings, is known as jungle yellow fever. If infected individuals move into a populated area, they may be bitten by a semidomestic species of mosquito, such as Aëdes aegypti, which lives close to human habitations. These feed on the blood of humans and are the chief transmitting agents in epidemics of urban yellow fever.
HISTORY
It is probable that the disease initially appeared in Africa and that it was brought to America at the time of the slave trade. The disease was first described in medical terms during the 17th century, when an outbreak was observed in the Yucatán Peninsula, Mexico. Ultimately yellow fever spread to the U.S., Spain, and other countries.
In 1881 the Cuban physician Carlos Finlay advanced the hypothesis that yellow fever is transmitted by mosquito bites. Finlay's theory was verified in 1901 by the work of several investigators, notably the American bacteriologist Walter Reed, who also proved the agent to be a virus. The disease was brought under control by advanced methods of sanitation, including drainage of mosquito breeding grounds and quarantine of ships arriving from infected areas.
SYMPTOMS
The incubation period of yellow fever is three to six days. In severe cases the onset is sudden, with typical symptoms of headache, backache, and fever. The first stage is also characterized by nausea, vomiting, and presence of albumin in the urine. After the initial fever, the temperature usually returns to normal, but on the fourth or fifth day the temperature again rises. This second stage is marked by jaundice, hemorrhage from mucous membranes, vomiting of blood (the characteristic, so-called black vomit of yellow fever), and fatty degeneration of the liver, kidneys, and heart. The destruction of liver cells results in the accumulation of yellow bile pigments in the skin, giving the disease its name. Death usually occurs between the fourth and eighth day after the onset. In cases of spontaneous recovery, convalescence is rapid, although jaundice may persist for some time. The disease never recurs, one attack providing immunity for life.
PREVENTION
No treatment is known for yellow fever. In 1939 the South African physician Max Theiler developed a vaccine that confers immunity to the disease. Vaccination is today required for all persons traveling between endemic regions and other parts of the world.
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