Infectious Diseases in an Age of Change The Impact of Human Ecology and Behavior on Disease Transmission (1995) / Chapter Skim
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Dengue: The Risk to Developed and Developing Countries
Dengue: The Risk to Developed and Developing Countries
Pages 43-58
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From page 43... ...
During this period the frequency of dengue fever epidemics has increased dramatically, hyperendemic transmission has been established over a geographically expanding range (Figure 1) , and DHF has occurred in new areas and at higher incidence.
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From page 44... ...
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From page 45... ...
TRANSMISSION CYCLE, DISEASE, AND PA11IOGENESIS Dengue is caused by four antigenically distinct single-strand positivepolarity RNA viruses, designated dengue types 1=, belonging to the family Flaviviridae (5~. Virus transmission in its simplest form involves the ingestion of viremic blood by mosquitoes and passage to a second susceptible human host.
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From page 46... ...
An important question for future research is whether the virus strains that circulate in the forest cycle are biologically distinct. Nonhuman primates challenged with strains of dengue virus isolated from humans generally develop abbreviated and significantly lower viremias than humans (7~.
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From page 47... ...
These antibodies are the result of prior infection with a heterologous dengue virus serotype, or, in the case of infants born to immune mothers, the result of waning passive maternal antibody. The infectious immune complexes gain access to Fc-receptor-bearing monocytes more readily than dengue virus alone, with the result that the host has a larger number of infected cells containing quantitatively higher amounts of dengue virus, a phenomenon known as immune enhancement.
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From page 48... ...
During the 1960s, dengue virus types 2 and 3 became established in the region, and in 1977, dengue type 1 was introduced, rapidly spread, and became endemic. The pattern of intermittent epidemics at long intervals and transient circulation of one serotype changed to one of annual outbreaks in multiple locations and persistent cocirculation of multiple dengue serotypes.
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From page 49... ...
Arrows indicate island nations affected in the Caribbean region. DENGUE IN THE DEVELOPED WORLD Every year 3~100 cases of dengue are reported in the United States in persons who have traveled to tropical countries.
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However, a subspecies A aegypti aegypti, evolved in Africa to become a highly domesticated animal, following humankind on its journeys and migrations to the corners of the globe, breeding in the artificial containers used for storing clean water, resting between blood meals in human habitations away from predators and harsh weather, flying rarely more than 50 yards from these convenient locations, and adopting wary biting habits around its observant and dexterous human prey.
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From page 51... ...
In those countries that had achieved eradication, mosquito control efforts sagged under the competition with other priorities for scarce health resources and with the increasing demands imposed by the conditions in bursting megacities such as Sao Paulo and Rio de Janeiro. Lack of funding, leadership, and morale eroded the once-proud mosquito control agencies (18~.
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From page 52... ...
. It was predicted that this aggressive and adaptable species would become implicated in the transmission of indigenous viruses, and this has in fact occurred; five different agents, including two human pathogens (eastern equine encephalitis and dengue viruses)
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From page 53... ...
Since variants with similar genetic structure are found within a specific geographic location, such studies have elucidated movements of dengue viruses and the source of epidemics. The results also suggest that genetic variation in virus strains may determine virulence and explain the changing patterns of disease.
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From page 54... ...
Thus, it appeared that the epidemics arose by introduction of dengue 2 virus from afar and were not the result of spill-over from the forest transmission cycle. The molecular analysis confirmed the role of humans in the dissemination of dengue viruses.
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From page 55... ...
demonstrating variation in the ability of dengue virus strains to replicate in human peripheral blood monocytes and higher replication of isolates from DHF patients than from dengue fever patients requires further evaluation and confirmation in prospective studies. FLAVIVIRUS AND DENGUE EVOLUTION: A BIOLOGICAL PERSPECTIVE AND SOME SPECULATIONS ON FUTURE CHANGES IN DENGUE EPIDEMIOLOGY The 68 recognized flaviviruses are classified into serological complexes, and these in turn correspond closely to their mode of transmission.
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From page 56... ...
The remarkable ability of dengue viruses to replicate to high titers in human tissues raises the possibility that, should a variant emerge with altered tropism—e.g., for epithelial tissues permitting shedding in respiratory secretions, or conversely for nervous tissues, permitting neuroinvasion the result could fundamentally change the route of transmission or the expression of disease in the host. While this may appear to be a remote possibility, we should remember that other flaviviruses, including the bat- and rodent-associated flaviviruses and simian hemorrhagic fever virus, have evolved in these directions.
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From page 57... ...
The emergence of a new serotype of dengue virus differing at one or more critical neutralization epitopes will thus undoubtedly occur at some time in the future. Dual infections of humans and vectors with different dengue serotypes may be an increasingly frequent event (35)
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From page 58... ...
(1989) in Dengue Hemorrhagic Fever: Diagnosis, Treatment and Control, ed.
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