Understanding Dengue: A Guide to the Mosquito-Borne Virus
Introduction
Dengue is an acute arthropod-borne viral infection that places a heavy socioeconomic and disease burden on many tropical and subtropical regions, and is the most frequent arboviral disease globally. Dengue is transmitted by the bite of an infected female mosquito. Non-vector transmission can also occur, for example, through blood transfusion, organ transplantation, needle stick injuries, and mucosal splashes.Transmitted by mosquitoes of the genus Aedes, dengue is found mainly in the tropics and subtropics, with over 3 billion people living in Aedes-infested areas. The annual incidence of dengue infections was estimated to be around 400 million per year.
Clinical Manifestations of the Three Dengue Phases
Febrile Phase
• High fever and chills. Typically persistent or unremitting, although a saddleback pattern can be observed. Children experience high fever and vomiting but are usually less symptomatic than adolescents and adults, except that febrile convulsions can occur.
• Fever lasts for 3–7 days from illness onset.
• Systemic symptoms such as headache, malaise, retro-orbital pain, arthralgia, myalgia, bone pain, nausea, vomiting, and altered taste sensation.
• Presence of upper respiratory symptoms helps to differentiate influenza from dengue.
• Examination findings can include rash, flush, conjunctival or pharyngeal injection, mild bleeding manifestations, generalised lymphadenopathy, and a palpable liver.
• A tourniquet test can be positive but is a non-specific finding.
Critical Phase
Vascular leak syndrome, bleeding, liver impairment, CNS impairment, cardiac impairment, eye impairment, impairment of other organs (Microscopic haematuria has been noted in 20 –30% of inpatients with dengue but AKI is rare generally. Renal failure is sometimes seen in profound DSS, or in association with rhabdomyolysis.)
Recovery Phase
• With good supportive care full recovery is usual within 1–2 weeks.
• Post-viral fatigue and depression are reported, but few studies have evaluated these outcomes prospectively.
• A florid convalescent rash can develop, resolving slowly over several weeks.
• Fever persisting for >10 days can indicate bacterial superinfection or development of rare complications, such as secondary haemophagocytic lymphohistiocytosis.
Diagnosis
* For Suspected Cases
Visit to a dengue-endemic area within 14 d prior to the onset of the disease, or the presence of dengue cases within 1 month around the place of residence or workplace, consistent with the clinical manifestations of dengue fever.
* For Clinical Diagnostic Cases
Serum specimens from suspected cases tested positive for dengue virus IgM antibodies or positive for NS1 antigen.
* For Confirmed Cases
Suspected cases or clinically diagnosed cases that meet one of the following: (1) Positive dengue virus nucleic acid test; (2) Culture isolation of dengue virus; (3) Positive seroconversion of dengue virus IgG antibodies in serum, or at least a fourfold rise in antibody titer during the convalescent phase as compared with the acute phase.
Laboratory Investigations
Etiological and Serological Examinations
Antigen Detection — Dengue virus NS1 antigen tests positive in blood during the acute febrile phase (By colloidal gold assay or ELISA)，NS1 is a glycoprotein that is common to all dengue serotypes and can be used to detect either primary or secondary infections in the earliest stages.
Nucleic Acid Detection — Dengue virus nucleic acid tests positive in specimens such as blood or cerebrospinal fluid (CSF).
Virus Isolation — Dengue virus is isolated via culture from specimens such as blood.
Serological Antibody Detection — Serology testing for dengue lgG and lgM can be useful in confirming primary or secondary diagnosis. IgM antibodies can be detected 3-5 days after symptom onset in primary infection patients, peak at 2 weeks, and persist for 2-3 months. A positive IgM test suggests recent dengue virus infection and is applicable for early diagnosis of dengue fever; however, cross-reactivity with other flaviviruses may occur. IgG antibodies can be detected approximately 1 week after symptom onset and may persist for years or even lifelong. Detection of high levels of IgG antibody within the first week of illness suggests a secondary infection.
General Examinations —Complete blood count (CBC), urinalysis, clinical chemistry tests, coagulation studies, ultrasonography, X-ray, CT, MRI, ECG and so on. All of the above can play a supportive role in diagnosis and treatment.
Getein’s Solutions
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