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The zoonotic viruses comprise of more than 400 viral 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 arthropod-borne or arboviruses are transmitted to humans by infected blood-sucking insects, such as mosquitoes, ticks, and Phlebotomus flies (sandflies). 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.


In most cases, the zoonotic viruses were first named after the place or region of initial isolation or reported infection (eg, St. Louis encephalitis virus, West Nile virus, Zika virus) or after the disease produced (eg, yellow fever). More recent studies have assigned the majority to families and genera on the basis of properties including morphologic and genetic features, geographic distribution, and disease spectrum summarized in Table 16–1. The major characteristics of these arboviruses families, including togaviruses, flaviviruses, bunyaviruses, and reoviruses are summarized in the following discussion.

TABLE 16–1Arboviruses of Major Importance to Humans

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