Nile Virus Home > Ecology
and Virology > Entomology
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.
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 (circulating
virus), and thus do not contribute to the transmission cycle.
the United States, West Nile virus is transmitted by
infected mosquitoes, primarily members of the Culex
Arboviral encephalitis can be prevented in two major ways:
protective measures to reduce contact with mosquitoes and
health measures to reduce the population of infected mosquitoes
in the environment.
protection measures include reducing time outdoors, particularly
in early morning and evening hours, wearing long pants and long
sleeved shirts, and applying mosquito repellent to exposed skin
areas and clothing.
health measures include elimination of larval habitats or spraying
of insecticides to kill juvenile (larvae) and adult mosquitoes.
The combination of mosquito control methods selected for use in
a control program depends on the time of year, the type of mosquitoes
to be controlled, and the habitat structure. In emergency situations,
wide area aerial spraying is used to quickly reduce the number
of adult mosquitoes. In many states, aerial spraying may be available
as a means to control nuisance mosquitoes. Such resources can
be redirected to areas of virus activity when necessary.
of aerial spraying costs during disease outbreaks is often provided
by state or local emergency funds. Federal funding of emergency
spraying is rare and almost always is associated with a natural
disaster such as flood or hurricane.