Yellow fever is a viral hemorrhagic disease that is mosquito borne. The virus belongs to the family of flavi virus and is a positive sense single stranded RNA virus which is about 50-60 nm in diameter. Infected mosquitoes transmit the virus through its saliva and the viral replication happens in regional lymph nodes and skin.Entering through receptor-mediated endocytosis the virus synthesizes RNA in the cytoplasm and protein in the endoplasmic reticulum and virions released trough membrane of the cell. Interaction of virulence factor proteins with cellular receptors results in the dentritic cells endocytose the virions and subsequently disseminating them.Yellow fever case-mortality rate is reported to be around 20% among patients with jaundice and up to 50% of patients severely affected die in case of no treatment (eMedicine).History of Yellow Fever.Yellow fever has been a cause of life threatening epidemics throughout the last few hundreds of years of human civilization. It is believed to have originated in Africa and transported to the western hemisphere through the slave trade with the first reported outbreak being in Yucatan in 1648 (Carter). The ensuing years reported a number of outbreaks in the Americas and Europe (Strode et al). The disease remained an enigma though Cuban Carlos Finlay suggested the mosquito Culex cubensis which is now called Aedes aegypti to be responsible for the spread of the disease (Bryan 275-292).