Dengue virus belongs to the family flaviviridae, a group of approximately 70 viruses, of which 30—6 commonly—have been associated with human disease. These are: dengue, yellow fever, West Nile encephalitis, St. Louis encephalitis, Japanese encephalitis, and tick-borne encephalitis. All are single-stranded RNA viruses that share common envelope proteins; which produces significant cross-reactivity.
Dengue virus has 4 subtypes, and infection with one subtype produces lifelong immunity to that subtype only. Subsequent reinfection with a second serotype has been implicated as a risk factor for increased disease severity and progression to dengue hemorrhagic fever and dengue shock syndrome. Serotype 3 is now the dominant strain currently circulating in Brazil.
Dengue fever is transmitted by mosquito vector, usually Aedes aegypti, although other Aedes species are potential vectors. A. aegypti has a worldwide distribution throughout most of the tropical and subtropical world, from 30° north to 20° south latitude. Dengue fever is largely a disease of urban centers, as the Aedes mosquito has adapted well to the city environment, with the dense human population providing stagnant fresh water supplies for mosquito breeding.
Humans are the reservoir of dengue fever. After biting an infected host, the mosquito remains infective for the rest of its life (average 2-8 weeks), potentially infecting multiple victims.(1, 2)
The World Health Organization estimates 50-100 million cases per year. The Pan American Health Organization reported 760,846 cases in 2007. Brazil alone had approximately 345,000 cases in 2006, and an average of 280,000 cases per year from 1981-2006. The rates of disease progression to dengue hemorrhagic fever range from 0.02% to 2%, with death rates of ∼10%.(3)
Dengue fever classically starts abruptly after a short 2-3 day incubation period, with fever, severe headache, malaise/fatigue, and severe arthralgia, that is, “break bone” fever. Headache and retro-orbital pain are characteristic, and fever is sometimes preceded by facial swelling. Fevers to 40.6°C (105°F) can occur for 5-7 days, accompanied by relative bradycardia. Patients then defervesce, only to have fever typically return days later (biphasic illness), that is, a “camelback fever” curve.(1, 2, 4, 5, 6, 7)
Bone marrow suppression is common, manifested by leukopenia and thrombocytopenia. Atypical lymphocytes are a constant feature of dengue fever. Serum transaminases are mildly elevated, and serum transaminases have a high negative predictive value arguing against the diagnosis of dengue fever.1, 2
Dengue fever can be diagnosed by demonstrating elevated dengue IgM (immunoglobulin M) enzyme-linked immunosorbent assay titers. Also diagnostic are convalescent titers demonstrating a 4-fold increase in IgG dengue titers.
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— Burke A. Cunha, MD, Diane Johnson, MD, Brian McDermott, DO
This article was originally published in the April 2009 issue of The American Journal of Medicine.
