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Epidemiology eassy on Yellow Fever
Pages 12 (3012 words)
Yellow fever is a viral hemorrhagic fever with high mortality that is transmitted by mosquitoes. The disease occurs now only in Africa and Central and South America, although historically, large outbreaks occurred in Europe and North America. Mosquitoes capable of transmitting yellow fever have never occurred.
The family Flaviviridae contains only one genus, Flavivirus. They are somewhat smaller than alphaviruses, being 40 nm in diameter. The name flavivirus refers to the type species, the yellow fever virus ( Flavus, L = Yellow).
The yellow fever virus was first isolated in 1927 by inoculating rhesus monkeys with the blood of an African patient named Asibi. The virus was shown by Theiler (1930) to grow well following intracerebral innoculation in mice. The infected mouse brain was used as a vaccine in former French West Africa (Dakar vaccine) though this was encephalitogenic. It was later replaced by a non-neurotropic (17D) vaccine (Panicker 2007, p.527-30).
Cases are classified as inapparent (< 48 h of fever and headache), mild, moderately severe and malignant. Incubation lasts 3 to 6 days. Prodromal symptoms are usually absent. Onset is sudden, with fever of 39 to 40C (102-104 F). The pulse, usually rapid initially, by the second day becomes slow for the degree of fever present (Faget's Sign). The face is flushed and the eyes are injected; tongue margins are red and the center is furred. Nausea, vomiting, constipation, headache, muscle pain (especially in the neck, back and legs), severe prostration, restlessness and irritability are common symptoms. ...
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