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Arboviruses (or arthropod-borne
viruses) are a heterogeneous group of viruses that share the same
usual route of entry into humans: via the bite of an infected mosquito,
tick, sandfly, or other arthropod.1,2 The life
cycle of most arboviruses is characterized by the ability of the
virus to replicate in both an arthropod vector and a vertebrate “natural” host
(usually birds or small mammals) and by transmission between these
two organisms at the time of the arthropod’s bite (eFig. 305.1).
This cycle leads to establishment or maintenance of the virus in
a given ecosystem. Humans or domestic animals are only “incidental” hosts
for many species of arboviruses, as infection in such hosts (although
capable of causing disease) is often a dead-end for the virus due
to viremia being too low or too transient to contribute to maintenance
of the cycle of transmission. Some viruses are specific to a single
genus or species of insect, while others are transmissible by multiple
vectors. In addition, some arthropods are capable of transovarial
transmission, wherein their eggs (which sometimes overwinter and
hatch in spring) are infected with the virus, allowing viral maintenance
in areas of colder climate.
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Arboviruses generally produce 1 of 4 clinical syndromes: (1)
central nervous system (CNS) disease, (2) febrile illness with rash, (3) arthropathy,
or (4) hemorrhagic fever syndrome.1 In North America,
encephalitis is the most commonly diagnosed manifestation of arboviral
infection, with several viruses producing sporadic disease as well
as outbreaks of infection each year. Table 305-1 provides
a list of arboviruses presenting with different symptom complexes,
and details the vector, reservoir, distribution, incubation period,
and the population most affected.
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