Your personal introduction to
With a total of 69 pathogens in its ranks, Flaviviridae contains a myriad of viruses that cause disease in humans. Foremost among these is Yellow Fever Virus, the type virus of the Flaviviridae, from which the family begets its name (flavus in Latin means "yellow").
Flaviviruses have been subdivided by the ICTV into three genera:
The Flavivirus genus contains several nasty critters including yellow fever virus, dengue fever virus, and Japanese encaphilitis (JE) virus. The Pestivirus genus is home to the three serotypes of bovine viral diarrhea, but no known human pathogens. Genus Hepacivirus consists of hepatitis C virus and its relatives. For an authoritative taxonomy visit the ICTV website.
Genus Flavivirus genomes consist of a monopartite (i.e., one piece of) linear, single-stranded, positive sense RNA. Because the RNA is positive sense, the nucleic acid itself is capable of instigating an infection in the appropriate host cells. The total genome can range from 10 to 11 kilobase pairs. The genome 3' terminus is not polyadenylated. The 5' end has a methylated nucleotide cap (allows for translation) or a genome-linked protein (VPg).
Genus Pestivirus genomes are reported to be 12.5 kb in length. Like the Flavivirus genus, no poly-A tail exists on the 3' end of the RNA, however, Pestivirus genus members lack a 5' cap. In both genera, structural genes are found towards the 5' end of the RNA.
Both the Pestivirus and theHepacivirus genus contain internal ribosomal entry sites (IRES) that provide a site of translation initiation for host ribosomes. This is in contrast to the Flavivirus genus that uses the technique of ribosomal scanning to commence protein synthesis.
Under the EM, virions appear roughly as spheres (some experts say they're "pleomorphic"), 40-65 nm in diameter. What can be seen under the microscope is the virus's lipid envelope, which it obtains from host cells during egress (leaving the cell). Underneath the envelope can be found an icosahedral capsid coat approximately 25-30 nm in diameter.
Click on image for a nifty picture of the morphology of flavivirus from the Universtat Wien.
All member's of the Flavivirus genus are transmitted by arthropods (ie, mosquitoes and ticks) while Hepatitis C is spread parenterally (ie, through contaminated bodily fluids). A key feature for viral transmission in Flaviviruses is that they are capable of reproducing in their vector. Without the ability to replicate in the vector, they would not remain viable to be passed from one host to the next. For further information I refer the surfer to last year's flavivirus page made by Valerie Oram. Further information about viral diseases you can only get from a bug, also known as "arboviruses", can be found at: http://fiona.umsmed.edu/~yar/arbo.html.
