The NIH says, "West Nile virus belongs to a group of disease-causing
viruses known as flaviviruses . . . Other flaviviruses include yellow
fever virus, Japanese encephalitis virus, dengue virus, and Saint
Louis encephalitis virus."

Why are they called flaviviruses?  What does the name mean, and where
did it come from?  (Does it have something to do with riboflavin, or
nothing to do with it?)

Hi Siggy,
Apparently the name comes from the Latin word "flavus" which means
"yellow".
"These viruses are known collectively as flaviviruses (from the Latin
flavus: yellow), because one of their most prominent members—the
yellow fever virus—produces jaundice in patients."
http://www.hfsp.org/pubs/brochures/Pub_Brochure.php?page=6
"The term Flavi, which comes from flavus meaning yellow, was adopted
from the type species, the Yellow Fever Virus."
http://web.centre.edu/bio/richey/bio455/flaviviruswebsite/
"Yellow Fever virus is the ptototype of this family (hence the name,
derived from flavus, Latin for « yellow »)."
http://edumed.unige.ch/apprentissage/virolab/bibliotheque/article.php3?id_article=23
I hope that helps!
regards,
Jackburton
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Search terms used: [ flaviviruses ], [ flaviviruses flavus ]

jackburton, that certainly answers it.  I suppose I was hoping for a
riboflavin connection in case more (or less) of that vitamin would
help.

arsenic, thanks for that too.

Also:  The name [Riboflavin] comes from Ribo (ribose) and flavin
(flavus-Latin for yellow)

http://www.mdschoice.com/elements/elements/other_elements/riboflavon.htm