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Yellow fever is caused by Yellow fever virus (YFV), an enveloped RNA virus 40–50 nm in width, the type species and namesake of the family Flaviviridae. It was the first illness shown to be transmissible by filtered human serum and transmitted by mosquitoes, by American doctor Walter Reed around 1900.
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Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. The illness can cause bleeding problems. It is called yellow because it makes the skin and the eyes yellow in color, like jaundice . There is a vaccine which can stop the disease, but many people in Africa and South America are not vaccinated against it.
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- Overview
- History
- The course of the disease
- Diagnosis, treatment, and control
yellow fever, acute infectious disease, one of the great epidemic diseases of the tropical world, though it sometimes has occurred in temperate zones as well. The disease, caused by a flavivirus, infects humans, all species of monkeys, and certain other small mammals. The virus is transmitted from animals to humans and among humans by several speci...
Western Africa has long been regarded as the home of yellow fever, although the first recorded outbreaks of the disease were in central and coastal South America after the Spanish conquest in the 16th century. For the next 300 years, yellow fever, given various names such as Yellow Jack and “the saffron scourge,” was one of the great plagues of the New World. The tropical and subtropical regions of the Americas were subjected to devastating epidemics, and serious outbreaks occurred as far north as Philadelphia, New York, and Boston but also as far away from the endemic centres as Spain, France, England, and Italy.
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By the late 19th century there were several theories about the cause and transmission of yellow fever. The Scottish medical historian Charles Creighton, writing in the ninth edition of the Encyclopædia Britannica (1885), pointed out that “yellow fever, in time and place, has dogged the steps of the African slave trade.” Dismissing as “altogether wide of the mark” recent suggestions that the disease might be passed by a microorganism, Dr. Creighton summarized the standard view that yellow fever was “a virulent filth-disease” brought to the New World in ships fouled by the excrement of African slaves:
To establish an epidemic in a distant port, it has been necessary that there should be carried thither a material quantity of the specifically poisonous harbour-filth in a ship’s bilges, and that the conditions favourable to its increase and diffusion by fermentation should exist in the new soil.
Treatment consisted of “vigorous measures” to purge the infection: doses of ipecacuanha to induce vomiting, castor oil to loosen the bowels, and enemas of cold water with turpentine to expel gas.
There are three substantially different patterns of transmission of the yellow fever virus: (1) urban, or classical, yellow fever, in which transmission is from person to person via the “domestic” (i.e., urban-dwelling) Aedes aegypti mosquito; (2) jungle, or sylvatic, yellow fever, in which transmission is from a mammalian host (usually a monkey) to humans via any one of a number of forest-living mosquitoes (e.g., Haemagogus in South America, A. africanus in Africa); and (3) intermediate, or savannah, yellow fever, in which transmission is from animal to person and from person to person via a number of “semidomestic” mosquitoes (e.g., A. furcifer, A. taylori).
The course of yellow fever is rapid. After the bite of the infecting mosquito, there is an incubation period of several days while the virus multiplies within the body. The onset of symptoms is then abrupt, with headache, backache, rapidly rising fever, nausea, and vomiting. This acute stage lasts two or three days, after which the patient either begins to recover or proceeds to a deeper toxic state marked by high fever, slow pulse rate, and the vomiting of dark blood. Death may occur six or seven days after the onset of symptoms. Because the virus destroys liver cells, jaundice (yellowing of the skin and eyes by deposition of bile pigment) is a common sign in persons with yellow fever.
In the early stages of yellow fever, its symptoms are similar to those of other tropical fevers such as malaria, leptospirosis, or dengue. Diagnosis is usually established by blood tests showing the presence of antibodies to the virus and by the patient’s history of having been in an area where the disease is endemic. Treatment is supportive and is designed to correct the acid–base imbalance and electrolyte abnormalities caused by vomiting, heart failure, and kidney derangements. Good nursing and supportive care, particularly in reducing fever, are important both in maintaining comfort and in reducing mortality.
Before the introduction of yellow fever vaccine, the control of Aedes aegypti mosquitoes was the only procedure for preventing occurrence of the disease. Immunization is now the most practical and reliable way to prevent yellow fever in people who live in and travel to areas where it is endemic. Still, control of mosquito populations is an essential component of any program designed to prevent the spread of yellow fever, particularly in urban areas. When people must travel or live in regions where the jungle transmission cycle is maintained, individual immunization is necessary. In these regions, human cases will continue as long as there remain unimmunized persons, for there is no known practical way of eliminating the virus of yellow fever from the animal and mosquito populations of the vast tropical forests in South America and Africa.
- The Editors of Encyclopaedia Britannica
The yellow fever epidemic of 1793 struck during the summer in Philadelphia, Pennsylvania, where the highest fatalities in the United States were recorded. The disease probably was brought by refugees and mosquitoes on ships from Saint-Domingue. It rapidly spread in the port city, in the crowded blocks along the Delaware River.
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