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INTRODUCTION

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The zoonotic viruses comprise more than 400 agents, one or more of which occur in most parts of the world. Members of the group have their ultimate reservoirs in insects or lower vertebrates. They are from diverse RNA virus families that primarily include the togaviruses, flaviviruses, bunyaviruses, reoviruses, arenaviruses, and filoviruses. The zoonotic viruses discussed here are divided into two groups: Arthropod-borne (arboviruses) and nonarthropod-borne zoonotic viruses. The arboviruses are transmitted to humans by infected blood-sucking insects, such as mosquitoes, ticks, and Phlebotomus flies (sandflies). Their major morphologic and genetic features are summarized in Table 16–1. The other zoonotic RNA viruses are generally believed to be transmitted by inhalation of infected animal excretions, by the conjunctival route, or occasionally by direct contact with infected animals (nonarthropod zoonotic viruses). Rabies virus, which is commonly transmitted by animal bites, is discussed separately in Chapter 17. Certain DNA viruses (poxviruses) are also transmissible from animals to humans, which are described in Chapter 11.

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TABLE 16–1Selected Arboviruses of Major Importance to Humans
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ARTHROPOD-BORNE ZOONOTIC ARBOVIRUSES

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VIROLOGY
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In most cases, the zoonotic viruses were first named after the place of initial isolation (eg, St. Louis encephalitis) or after the disease produced (eg, yellow fever). More recent studies have assigned the majority to families and genera on the basis of properties indicated in Table 16–1. The major characteristics of these arbovirus families, including togaviruses, flaviviruses, bunyaviruses, and reoviruses are summarized below.

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Often named after place of initial isolation

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TOGAVIRUSES

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Togaviruses are from Togaviridae family and Alphavirus genus includes arboviruses within this family that infect humans. The other genus, Rubivirus that includes rubella virus is discussed in Chapter 10. Alphaviruses have enveloped virions containing single-stranded, positive-sense RNA genome measuring 70 nm in external ...

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