Yellow fever is an infection caused by an arbovirus (arthropod-
borne virus -- a virus carried by insects). There are over 300
known arboviruses, over 150 of which are known to infect humans;
other arboviral diseases include several types of equine
encephalitis and other kinds of encephalitis including dengue
fever, St. Louis encephalitis, and West Nile virus, The latter
three diseases, and yellow fever, are caused by viruses
belonging to the "Flaviviridae" family of arboviruses. Most
arboviruses are usually found in nature in birds and small
animals, and people are infected accidentally when bitten by
carrier insects, or when transfused with blood from an infected
donor. Yellow fever and dengue fever are exceptions: these
viruses only infect humans, and are carried from person to
person by insects. Yellow fever has three stages. Stage I
consists of fever, malaise (feeling lousy), headaches, weakness,
nausea, and vomiting (sounds like the flu, doesn't it?). In
stage II most of the symptoms go away, or at least