Syn: Arbovirus Encephalitis
Arthropod-borne viruses (arboviruses)
are a large heterogeneous group of viruses transmitted between
vertebrates by blood sucking arthropod vectors, such as mosquitoes
and ticks.
Replication of the virus in vertebrates
causes severe illness, but in the arthropod it is harmless.
Most virus infection are zoonoses among
wild and domestic animals, especially birds and mammals.
Man becomes accidentally infected if
bitten by an infected arthropod.
There are a number of arboviruses that
cause meningoencephalitis in man, and each of the arthropod-borne
viral encephalitis is confined to a particular geographic area and a
specific vector.
Visit:
Amebic Meningoencephalitis
;
Viral hemorrhagic fevers
In temperate zones, the climatic
effects the breeding of arthropods and the abundance of vertebrate
hosts, thus resulting in seasonal variation in each disease.
In tropical areas seasonal variation is
less pronounced.
The arthropod transmits the virus to a
person from one of the reservoir animals but not from another person.
People of all ages are susceptible to
these diseases.
Clinical symptoms range from a mild
grippe-like illness to fulminating and fatal encephalitis.
The encephalitis usually begins
abruptly, with fever, headache, disturbed consciousness and sometimes
signs of meningitis, convulsions, or paralysis.
The clinical course is usually short,
not chronic as in some other viral infections.
The diseases share many common
features, but each type has a different course.
For example, Eastern equine
encephalitis is commonly a severe fulminant encephalitis that kills in
a few days, where as Venezuelan equine encephalitis is a mild disease.
Histologic findings in these
encephalitides are usually confined to the central nervous system and
are similar for all types.
The lesions range from a mild
meningitis with scattered lymphocytes to more severe inflammation of
the gray matter, mainly around neurons, to prominent necrosis.
Perivascular cuffing appears in the
acute phase.
In contrast to the other infections,
Eastern equine encephalitis exhibits neutrophilic rather than
lymphocytic inflammation and extensive meningitis, resembling a
pyogenic infection.
Vasculitis and thrombosis lead to
numerous foci of necrosis, which extend into the white matter.
Some of the necrotic foci
resemble microabscesses.
Some important
arboviruses include:
Alphaviruses (Eastern Equine encephalitis ; Western
Equine encepahlitis ; Venezuelan equine encephalitis) ;
Flaviviruses
(
St.Louis Encephalitis ;
Japanese Encephalitis
;
Yellow Fever
;
Dengue
;
West Nile Virus
) ;
Bunyaviruses (LaCrosse encephalitis; Reoviruses;
Colorado tick fever).
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