Dengue and other emerging arbovirus diseases

About 177 pathogens are recognized as re-emerging or emerging, of which 73 percent are estimated to be zoonotic (Woolhouse and Gowtage-Sequeria, 2005) -that is, they are maintained in transmission cycles that involve domestic and/or wild animals, but can infect humans. Many, like dengue, are arboviral diseases, a term that describes a virus that requires a blood-sucking (hematophagous) arthropod, like a mosquito or tick, to complete its lifecycle. Except for dengue, which has fully adapted to an A. aegypti-human-A. aegypti cycle in tropical urban settings, all arboviruses have a non-human reservoir host, like a bird, rodent, or monkey. Of the more than 534 registered zoonotic and arboviruses, about 130 have been documented to cause illness in humans. Those of public health significance belong to three families: Flaviviridae (e.g. dengue fever, yellow fever, West Nile Virus), Togaviridae (e.g. Chikungunya fever, Ross River virus), and Bunyaviradae (Rift Valley fever, California encephalitis) (Gubler, 2002). The past few decades have seen a significant increase in the frequency, geographic spread, and virulence of a number of arboviral diseases. Table 4.2 provides a selective list of urban arbo-viral diseases that have public health importance. As vector-borne diseases require warm climates and moisture to thrive, they emerge more readily in tropical climates. However, many arthropod vectors are active during the summer but can "over-winter" in temperate climates.

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