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Health Centre

Dengue Fever

  • Introduction
  • Cause and Pathogenesis
  • Symptoms and Signs
  • Investigations and Diagnosis
  • Treatment and Prognosis
  • Prevention

  • Introduction

    Dengue fever is a disease caused by infection with a type of virus called Flavivirus. There are four different subtypes of this virus producing varying manifestations of the disease. The disease is spread through the bites of mosquitoes belonging to the Aedes egypti species. The disease is essentially a tropical one and is endemic in large parts of Latin and South America. Of late, its incidence has been on the increase in Asian countries such as India.

    Cause and Pathogenesis

    Dengue fever is transmitted to humans by the bite of the infected Aedes egypti mosquito. The Aedes mosquito breeds in relatively fresh water, lives close to human habitations and bites during the day. The incubation period between the bite and the onset of symptoms is usually two to seven days. The Aedes mosquito is also responsible for the spread of diseases such as yellow fever and Chikungunya virus fever.

    Symptoms and Signs

    A large number of infections may be sub-clinical, that is, the patients may not even be aware that they have had the disease. The infection usually manifests itself as fever with severe body pain or myalgia. There may be an associated rash over parts of the body. The body pain is so intense that this disease has been called break-bone fever. Quite often, the disease makes no further progress and the patients recover. However, some patients may develop involvement of either of the two dreaded syndromes in Dengue - bleeding (called DHF or Dengue Hemorraghic Fever) or involvement of the brain with altered consciousness (encephalitis). Fatalities are higher among patients in whom these complications are present. Joint pain is another symptom though there may not be true arthritis. Associated symptoms include severe headache, vomiting, and photophobia. Examination of the patient may reveal few findings such as a rash and pain on palpation of the muscles. These symptoms usually last for a period of two to five days and most patients who do not have complications recover completely.

    The risk of complications appears to be greater in children, particularly the risk of bleeding and DHF with its high fatality rate. Some patients may also go into shock, a condition known as Dengue Shock Syndrome (DSS). This too carries a higher risk of mortality.

    Investigations and Diagnosis

    The diagnosis of dengue is based on the clinical presentation, knowledge of the area in which the person lives, and laboratory investigations. Blood tests may show a low white blood cell count, a low platelet count, and elevation of certain enzymes.

    The definitive diagnosis is, however, made by isolating the virus in the blood of the individual during the acute phase of the disease or by detecting antibodies to the virus in the blood. Antigen detection is also possible. A rise in the antibody titre is a useful method of diagnosis. Investigations also need to be done to rule out other likely causes of fever such as malaria, and leptospirosis.

    Treatment and Prognosis

    Treatment is usually supportive and symptomatic. Analgesics, anti-pyretics, and broad-spectrum antibiotics are used during the acute phase to minimise the risk of secondary infection. In cases of bleeding, blood transfusions are required. Shock, if present, needs to be aggressively treated with fluids, oxygen, and close monitoring. Most patients will recover without any sequel. The overall mortality rate with effective treatment is close to 1% but this may be higher in children.


    Control and elimination of mosquito population is the best method of prevention. A vaccine is in the late stages of development but is still not available for commercial use on a large scale. Control of the mosquito population reduces the incidence of dengue, yellow fever, and certain other rare fevers that are also transmitted by the same species of mosquito.


    Dr. V.Ramasubramaniam MBBS, MD, MRCP.

    Dr.V.Ramasubramaniam is an Assistant Professor of Medicine and heads the Division of Infectious Diseases at the Sri Ramachandra Medical College and Research Institute

    More about Dr Ramasubramaniam.

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