Yellow fever epidemiology and demographics: Difference between revisions
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==Epidemiology and Demographics== | ==Epidemiology and Demographics== | ||
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|[[File:Areas with Risk of Yellow Fever Virus Transmission in Africa.jpg|thumb|400px|Areas with Risk of Yellow Fever Virus Transmission in Africa<br><small>Image obtained from CDC<ref>{{cite web|url=http://www.cdc.gov/yellowfever/maps/africa.html| title=CDC - Areas with Risk of Yellow Fever Virus Transmission in Africa}}</ref></small> | |||
Yellow fever occurs only in Africa, South and Central America, and the Caribbean.<ref>{{cite web|url=http://www.who.int/csr/disease/yellowfev/impact1/en/index.html |title= Yellow fever: a current threat |accessmonthday= June 25 |accessyear=2006 |publisher=WHO |}}</ref> Most outbreaks in South America are to people who work within the tropical rain forests and have direct contact with the organisms within the rainforest. | Yellow fever occurs only in Africa, South and Central America, and the Caribbean.<ref>{{cite web|url=http://www.who.int/csr/disease/yellowfev/impact1/en/index.html |title= Yellow fever: a current threat |accessmonthday= June 25 |accessyear=2006 |publisher=WHO |}}</ref> Most outbreaks in South America are to people who work within the tropical rain forests and have direct contact with the organisms within the rainforest. | ||
The disease can remain locally unknown in humans for long periods of time and then suddenly break out in an epidemic fashion. In Central America and Trinidad, such epidemics have been due to a form of the disease (''jungle yellow fever'') that is kept alive in Red Howler monkey populations and transmitted by ''[[Haemagogus]]'' [[mosquito]] species which live only in the canopy of rain forests. The virus is passed to humans when the tall rainforest trees are cut down. Infected woodcutters can then pass on the disease to others via species of ''Aedes'' mosquitoes that typically live at low altitudes, thus triggering an epidemic.<ref name=Theiler_1973>{{cite book | author = Theiler, Max and Downs, W. G. | title = The Arthropod-Borne Viruses of Vertebrates: An Account of The Rockefeller Foundation Virus Program 1951-1970 | edition = | publisher = Yale University Press | year = 1973 | id = ISBN 0-300-01508-9 }}</ref> | The disease can remain locally unknown in humans for long periods of time and then suddenly break out in an epidemic fashion. In Central America and Trinidad, such epidemics have been due to a form of the disease (''jungle yellow fever'') that is kept alive in Red Howler monkey populations and transmitted by ''[[Haemagogus]]'' [[mosquito]] species which live only in the canopy of rain forests. The virus is passed to humans when the tall rainforest trees are cut down. Infected woodcutters can then pass on the disease to others via species of ''Aedes'' mosquitoes that typically live at low altitudes, thus triggering an epidemic.<ref name=Theiler_1973>{{cite book | author = Theiler, Max and Downs, W. G. | title = The Arthropod-Borne Viruses of Vertebrates: An Account of The Rockefeller Foundation Virus Program 1951-1970 | edition = | publisher = Yale University Press | year = 1973 | id = ISBN 0-300-01508-9 }}</ref> | ||
Revision as of 14:39, 19 December 2014
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Yellow fever Microchapters |
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Diagnosis |
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Treatment |
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Treatment |
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Yellow fever epidemiology and demographics On the Web |
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American Roentgen Ray Society Images of Yellow fever epidemiology and demographics |
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Risk calculators and risk factors for Yellow fever epidemiology and demographics |
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Epidemiology and Demographics
| [[File:Areas with Risk of Yellow Fever Virus Transmission in Africa.jpg|thumb|400px|Areas with Risk of Yellow Fever Virus Transmission in Africa Image obtained from CDC[1]
IncidenceDuring interepidemic periods, low-level transmission may not be detected by public health surveillance. Such interepidemic conditions may last years or even decades in certain countries or regions. This “epidemiologic silence” does not equate to absence of risk and should not lead to travel without the protection provided by vaccination. Surveys in rural West Africa during “silent” periods have estimated an annual incidence of yellow fever of 1.1-2.4 cases per 1,000 persons and 0.2-0.5 deaths per 1,000 persons. YFV transmission in rural West Africa is seasonal, with elevated risk during the 2-4 months that the rainy season ends and the dry season begins (usually July-October); therefore, the annual incidence reflects incidence during a transmission season of 2-4 months. The incidence of yellow fever in South America is lower than that in Africa because the mosquitoes that transmit the virus between monkeys in the forest canopy do not often come in contact with humans and because immunity in the indigenous human population is high. Urban epidemic transmission has not occurred in South America for many years, although the risk of introduction of the virus into towns and cities is ever present. For travelers, the risks of illness and death due to yellow fever are probably 10 times greater in rural West Africa than in South America; the risk varies greatly according to specific location and season. In West Africa, virus transmission is highest during the late rainy and early dry seasons (July-October). In Brazil, the risk of infection is highest during the rainy season (January-March) . The low incidence of yellow fever in South America, generally a few hundred reported cases per year, could lead to complacency among travelers. However, it is important to note that four of the six cases of yellow fever reported among travelers from the United States and Europe in 1996-2002 acquired yellow fever in South America . All six cases were fatal and occurred among unvaccinated travelers. An increase in enzootic and epizootic yellow fever transmission in South America during the 1990s and the potential for epidemiologic change in the Americas remains a concern The risk of acquiring yellow fever is difficult to predict because of variations in ecologic determinants of virus transmission. As a rough guideline, the risks of illness and death due to yellow fever in an unvaccinated traveler in endemic areas in West Africa during the highest risk season from July to October have been estimated at 100 per 100,000 and 20 per 100,000 per month, respectively; for a 2-week stay, the estimated risks of illness and death were 50 per 100,000 and 10 per 100,000, respectively . The risks of illness and death in South America are probably 10 times lower (5 per 100,000 and 1 per 100,000, respectively for a 2-week trip) . These estimates are based on risk to indigenous populations and may not accurately reflect the true risk to travelers, who may have a different immunity profile, take precautions against getting bitten by mosquitoes, and have less outdoor exposure. Based on data for U.S. travelers during 1996-2004, the overall risk for serious illness and death due to yellow fever in travelers has been roughly estimated to be 0.05 -0.5 per 100,000 travelers to yellow fever-endemic areas. This range reflects an unvaccinated population of 10-90% and assumes that all travelers visiting holo-endemic countries are at risk and 10% of travelers to non holo-endemic countries are visiting risk areas. References
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