Dr  Sampurna Roy  MD

Dengue the most prevalent arthropod-borne viral (Arborvirus) disease of humans caused by  four  serotypes of dengue virus (DENV 1-4) of the genus Flavivirus.

It is transmitted to man by mosquito  Aedes aegypti. It is common in tropical and subtropical countries, especially in coastal areas. (World distribution of dengue viruses and their mosquito vector, Aedes aegypti : CDC)

Source: Man is infective to mosquito and mosquito transmits the disease to man.

Clinical presentation:

Clinically, symptoms start 6 days after of infection as malaise and headache, followed by sudden onset of fever, intense backache and generalized pains, mainly in the orbital and periarticular areas. After an afebrile interval of 24 to 48 hours, there is recurrence of fever for a day or two (‘saddleback fever’). There may be skin rash and lymphadenopathy.

In persons, previously exposed to Dengue virus, antiviral antibodies may enhance the uptake of virus into host cells and cause disseminated intravascular coagulation, shock and death (hemorrhagic dengue).

Pathological features:

Biopsy studies of the rash seen in nonfatal dengue fever show a lymphocytic vasculitis in the dermis.

In cases of fatal dengue hemorrhagic fever the gross findings are petechial hemorrhages in the skin and hemorrhagic effusions in the pleural, pericardial and abdominal cavities. Hemorrhage and congestion are seen in many organs. Histopathological examination show hemorrhage, perivascular edema and focal necrosis but no vasculitic or endothelial lesions. It is believed that most of the morphologic abnormalities seen result from disseminated intravascular coagulation and shock.

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Differential diagnosis : Includes malaria , typhoid fever, leptospirosis,  West Nile virus infection, measles , rubella, acute human immunodeficiency virus conversion disease, Epstein–Barr virus infection, viral hemorrhagic fevers, rickettsial diseases, early severe acute respiratory syndrome (SARS), and any other disease that can manifest in the acute phase as an undifferentiated febrile syndrome.

Diagnosis:  A confirmed diagnosis is established by culture of the virus, polymerase-chain-reaction (PCR) tests, or serologic assays.

The diagnosis of dengue hemorrhagic fever is made on the basis of the following triad of symptoms and signs:  Hemorrhagic manifestations; a platelet count of less than 100,000 per cubic millimeter; and objective evidence of plasma leakage, shown either by fluctuation of packed-cell volume (greater than 20 percent during the course of the illness) or by clinical signs of plasma leakage, such as pleural effusion, ascites, or hypoproteinemia. Hemorrhagic manifestations without capillary leakage do not constitute dengue hemorrhagic fever.