Communicable Diseases

Dengue Fever

Identification

An acute febrile viral disease characterized by sudden onset, fever for 2–7 days (sometimes biphasic), intense headache, myalgia, arthralgia, retro-orbital pain, anorexia, nausea, vomiting and rash. Early generalized erythema occurs in some cases. A generalized maculopapular rash may appear about the time of defervescence. Rash is frequently not visible in dark-skinned patients. Minor bleeding phenomena, such as petechiae, epistaxis or gum bleeding, may occur at any time during the febrile phase. With underlying conditions, adults may have major bleeding phenomena, such as GI hemorrhage in peptic ulcer cases or menorrhagia. Dengue fever with unusual hemorrhage should be differentiated from DHF with increased vascular permeability, bleeding manifestations and involvement of specific organs. Recovery may be associated with prolonged fatigue and depression. Lymphadenopathy and leukopenia with relative lymphocytosis are usual; mild thrombocytopenia (less than 100 × 103 cells per mm3; or 100 SI units × 109 per L) and elevated transaminases occur less frequently. Epidemics are explosive, but fatalities, usually rare, can be minimized by timely medical intervention.

Differential diagnosis includes chikungunya and other epidemiologically relevant diseases listed under arthropod-borne viral fevers; influenza; measles; rubella; malaria; leptospirosis; typhoid; scrub typhus; and other systemic febrile illnesses, especially those accompanied by rash.

Laboratory confirmation of dengue infection is through detection either of virus in acute phase blood/serum within 5 days of onset of illness, or of specific antibodies in convalescent phase serum obtained 6 days or more after onset of illness. Virus identification in blood is by reverse transcriptase polymerase chain reaction (RT-PCR), culture in mosquito cell lines, or inoculation to mosquitoes then identified through immunofluorescence with serotype-specific monoclonal antibodies. These procedures provide a definitive diagnosis, but practical considerations limit their use in endemic countries. The IgM capture ELISA is the most commonly used serological procedure for diagnosis, and is particularly suitable for high-volume testing. IgM antibody, indicating current or recent infection, is usually detectable 6–7 days after onset of illness. A positive test result in a single serum indicates presumptive recent infection; a definitive diagnosis requires increased antibody levels in paired sera. New immunoassays that detect dengue non-structural protein-1 (NS1) show some promise in diagnosis early in the febrile phase, prior to IgM rise. RT-PCR amplification protocols using dengue oligonucleotide primers can also detect dengue virus RNA in tissue from fatal cases. PCR with specific primers can distinguish among the dengue virus serotypes; PCR with nucleotide sequencing can characterize dengue strains and genotypes. Since these genome-based assays are costly, demand meticulous technique, and are highly prone to false-positives through contamination, they are not yet applicable for wide use in all settings.

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