Yellow fever was the first illness shown to be transmissible by filtered human serum and transmitted by mosquitoes, by Walter Reed around 1900. The positive-sense, single-stranded RNA is around 11,000 nucleotides long and has a single open reading frame encoding a polyprotein. Host proteases cut this polyprotein into three structural (C, prM, E) and seven nonstructural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, NS5); the enumeration corresponds to the arrangement of the protein coding genes in the genome. Minimal yellow fever virus (YFV) 3'UTR region is required for stalling of the host 5'-3' exonuclease XRN1. The UTR contains PKS3 pseudoknot structure which
Yellow fever titer (compared to an earlier sample) can confirm yellow fever. Together with clinical symptoms, the detection of IgM or a four-fold increase in IgG titer is considered sufficient indication for yellow fever. Since these tests can cross-react with other flaviviruses, such as dengue virus, these indirect methods cannot conclusively prove yellow fever infection. Liver biopsy can verify inflammation and necrosis of hepatocytes and detect viral antigens. Because of the bleeding tendency of yellow fever patients, a biopsy is only advisable "post mortem" to confirm the cause of death. In a differential diagnosis, infections with yellow fever must be distinguished from