Arthropod-borne
viruses (termed "arboviruses") are viruses that are maintained
in nature through biological transmission between susceptible vertebrate
hosts by blood-feeding arthropods (mosquitoes, sand flies, ceratopogonids
"no-see-ums", and ticks). Vertebrates can become infected
when an infected arthropod bites them to take a blood meal. The
term 'arbovirus' has no taxonomic significance.
The arboviral encephalitides are zoonotic, being maintained in complex
life cycles involving a nonhuman primary vertebrate host and a primary
arthropod vector. These cycles usually remain undetected until humans
encroach on a natural focus, or the virus escapes this focus via
a secondary vector or vertebrate host as the result of some ecologic
change. Humans and domestic animals can develop clinical illness
but usually are incidental or "dead-end" hosts because
they do not produce significant viremia, and do not contribute to
the transmission cycle.
Nomenclature
·
Family: Flaviviridae
· Genus: Flavivirus Japanese Encephalitis Antigenic Complex
· Complex includes: Alfuy, Cacipacore, Japanese encephalitis,
Koutango, Kunjin, Murray Valley encephalitis, St. Louis encephalitis,
Rocio, Stratford, Usutu, West Nile, and Yaounde viruses.
· Flaviviruses: share a common size (40-60nm), symmetry (enveloped,
icosahedral nucleocapsid), nucleic acid (positive-sense, single stranded
RNA approximately 10,000-11,000 bases), and appearance in the electron
microscope. Therefore, images of West Nile virus are representative
for this group of viruses.
