Biomedical Engineering Reference
In-Depth Information
encephalitis-producing viruses, that have specific geographic distributions:
Japanese encephalitis virus (mosquito-borne), Murray Valley encephalitis virus
(mosquito-borne), St. Louis encephalitis virus (mosquito-borne), West Nile
encephalitis virus (mosquito-borne), and a host of viruses collectively known as
tick-borne encephalitis viruses.
Yellow fever virus seems to have originated in Africa and spread
to other continents in the mid-seventeenth century. It is responsible for
hundreds of thousands of deaths in North America alone. The disease is
carried by primates, including humans, and transmitted from person to
person by the bite of a mosquito (Aedes aegypti). It produces hepatitis and
hemorrhaging (hence, it is included among the hepatitis viruses and the
hemorrhagic fever viruses).
Yellow fever virus is associated with an impressive number of medical
breakthroughs, being the first disease demonstrated to be transmitted by an
arthropod, among the first disease shown to be caused by a virus, and among
the first infections controlled by a live vaccine. Effective methods of yellow
fever prevention, through the eradication of the Aedes aegypti were developed
in the 1890s, and an effective vaccine was developed in the 1930s. Today,
there are about 200 000 cases of yellow fever, worldwide, with about 30 000
deaths [134]. Most infections occur in Africa.
While the incidence of yellow fever has diminished over the past century,
the incidence of dengue fever is increasing. Dengue, like yellow fever, is
transmitted primarily by the Aedes aegypti mosquito. More than 50 million
dengue virus infections occur each year, worldwide. Most infections are
asymptomatic or cause only mild disease, but a minority of infections are
severe and may cause death. Typical cases exhibit fever and intense pain in
muscles and joints (hence the alternate name of the disease, breakbone
fever). Fevers can come and go. Capillary permeability is a common feature
of the disease, and this may result in petechiae, the egress of fluid from
the vascular compartment, shock (so-called Dengue shock syndrome), and
hemorrhage (hemorrhagic syndrome). Severe cases of dengue, if untreated,
may have a fatality rate approaching 20%. Like yellow fever, dengue is
included in the group of hemorrhagic viruses.
The hepatitis G virus group, in Class Flaviviridae, contains only one
species, hepatitis G virus, which had been traditionally included among the
named hepatitis viruses. Hepatitis G is now considered to be an “orphan
virus” (i.e., a virus that has no associated disease). The hepatitis G virus is
found in a small percentage of donated blood units.
Group IV (
)ssRNA
Picornaviridae
Enterovirus
*Coxsackievirus
*Echovirus
1
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