and in vertebrates. The arthropod may become infected
Many others are associated with wildlife and spread is often
when it takes a blood meal from a viremic vertebrate.
from animal to man (e.g., most of the arboviruses, rabies
After replication of the virus in the arthropod, it can
virus, the hantaviruses, and the arenaviruses). The hanta-
be transmitted to a vertebrate when the arthropod takes
viruses (family Bunyaviridae) and arenaviruses (family
another blood meal. Although arboviruses tend to have
Arenaviridae) are associated with small rodents, in which
broad host ranges, a virus is usually maintained in only
they cause little disease. Humans, in which these viruses
one or a few vertebrate hosts and vectored by a limited
(e.g., Lassa fever virus; Junin virus, the causative agent of
set of arthropods.
Argentine hemorrhagic fever; and Sin Nombre virus, the
Therapeutic blood transfusion, use of hypodermic
causative agent of hantavirus pulmonary syndrome) cause
injections, and intravenous drug use are methods of spread
serious illness, can become infected by inhaling aerosols
of many blood-borne viruses. HIV, hepatitis B virus
containing excreta from infected rodents. Rabies virus
(family Hepadnaviridae), and hepatitis C virus (genus
(family Rhabdoviridae) is associated with unvaccinated
Hepacivirus, family Flaviviridae), for example, are com-
domestic dogs and with many species of wildlife, includ-
monly spread among drug users through sharing of con-
ing foxes, coyotes, skunks, raccoons, and bats. It is spread
taminated needles. Transfusion with contaminated blood
by the bites of infected animals. The virus is present in sali-
is still possible despite diagnostic tests to identify infected
vary fluid of the infected animal, and the disease induces
blood products. In developed countries, the blood supply
an infected animal to become aggressive and bite potential
is screened for HIV and hepatitis B and C viruses, as well
hosts. Interestingly, although many humans die worldwide
as other viral agents for which tests exist, but in devel-
of rabies each year contracted from the bites of rabid ani-
oping countries contaminated blood is often still a major
mals, human-to-human transmission does not occur. Some
problem. Blood-borne viruses that are not arboviruses are
other human infections have been contracted from wildlife
often spread sexually as well as by the methods stated ear-
only indirectly. Nipah virus (family Paramyxoviridae) is
lier, but in some cases it is not clear how the viruses were
associated with flying foxes, large fruit-eating bats. The
spread before the introduction of blood transfusion and
virus recently caused an epidemic of disease in pigs in
hypodermic needles.
Malayasia and Singapore, and pig farmers contracted the
Because of the need to establish a significant viremia,
disease from the pigs. Before the epidemic died out, 258
which requires extensive viral production in organs that can
humans developed encephalitis, of which 40% died.
shed virus into the bloodstream, blood-borne viruses often
cause serious disease. Furthermore, because spread is direct,
these viruses need not be stable outside the body and usually
have a short half-life outside an organism.
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