Evol. endemic and epidemic Dengue

Evol. endemic and epidemic Dengue - JOURNAL OF VIROLOGY,...

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J OURNAL OF VIROLOGY, 0022-538X/00/$04.00 1 0 Apr. 2000, p. 3227–3234 Vol. 74, No. 7 Copyright © 2000, American Society for Microbiology. All Rights Reserved. Evolutionary Relationships of Endemic/Epidemic and Sylvatic Dengue Viruses ERYU WANG, 1 HAOLIN NI, 1 RENLING XU, 1 ALAN D. T. BARRETT, 1 STANLEY J. WATOWICH, 2 DUANE J. GUBLER, 3 AND SCOTT C. WEAVER 1 * Department of Pathology and Center for Tropical Diseases, University of Texas Medical Branch, Galveston, Texas 77555-0609 1 ; Department of Human Biological Chemistry and Genetics and Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, Texas 77555-0645 2 ; and Division of Vector-Borne Infectious Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado 80522 3 Received 28 October 1999/Accepted 4 January 2000 Endemic/epidemic dengue viruses (DEN) that are transmitted among humans by the mosquito vectors Aedes aegypti and Aedes albopictus are hypothesized to have evolved from sylvatic DEN strains that are transmitted among nonhuman primates in West Africa and Malaysia by other Aedes mosquitoes. We tested this hypothesis with phylogenetic studies using envelope protein gene sequences of both endemic/epidemic and sylvatic strains. The basal position of sylvatic lineages of DEN-1, -2, and -4 suggested that the endemic/epidemic lineages of these three DEN serotypes evolved independently from sylvatic progenitors. Time estimates for evolution of the endemic/epidemic forms ranged from 100 to 1,500 years ago, and the evolution of endemic/epidemic forms represents relatively recent events in the history of DEN evolution. Analysis of envelope protein amino acid changes predicted to have accompanied endemic/epidemic emergence suggested a role for domain III in adaptation to new mosquito and/or human hosts. Dengue viruses (DEN) ( Flaviviridae : Flavivirus ) are serious human pathogens that occur nearly throughout the tropics, with ca. 100 million cases annually (16). DEN comprise four serotypes (DEN-1 to DEN-4); although epidemiologically sim- ilar, they are genetically and antigenically distinct. Infection with one serotype leads to lifelong protection against homol- ogous reinfection but only brief protection against heterolo- gous challenge (21, 38). DEN cause dengue fever, a self-limited febrile illness lasting 2 to 10 days that has been known in the medical literature for over 200 years. Infrequent epidemics of dengue fever occurred in tropical areas until the 1950s. After War World II, this pattern of disease was disrupted by the emergence of dengue hemorrhagic fever and dengue shock syndrome, more severe diseases characterized by thrombocytopenia, hemorrhage, and excessive plasma leakage (16, 28). Two principal hypotheses have been proposed to explain the hemorrhagic form of dis- ease: (i) the immune enhancement theory maintains that hem- orrhage occurs in secondary infections when DEN-specific an- tibodies and memory T cells resulting from primary infection
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Evol. endemic and epidemic Dengue - JOURNAL OF VIROLOGY,...

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