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Dengue

Cause of the disease


Dengue

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Dengue is an infectious disease caused by the dengue virus (DENV). It belongs to the genus Flavivirus of the Flaviviridae family, which in turn, belongs to the group of Arboviruses (arthropod-borne viruses). The viral particles contain single-stranded RNA that are enwrapped and approximately 40-50 nm in diameter.

There are 4 serotypes called DENV-1, DENV-2, DENV-3 and DENV-4. Infection with one serotype produces lifelong immunity against that serotype reinfection. Successive infection with two different serotypes is a risk factor for developing the severe forms of the disease.

All serotypes have been isolated in the Americas. In several countries they circulate simultaneously, creating a serious risk for an epidemic.

 How is it transmitted?


Aedes aegypti

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The Aedes aegypti and Aedes albopictus mosquitoes are transmitters of dengue. The Aedes aegypti female mosquitos are the main source of dengue transmission. These species bite during the day, with the most active feeding period 2 hours before and after dawn and dusk. The mosquito bites an infected person and ingests blood with the dengue virus, which incubates in the mosquito for a period of 8 to 12 days, after which the mosquito begins to transmit the virus biting others. The newly infected person may have symptoms after 5-7 days of infection. Immediate mechanical transmission can also occur when the mosquito interrupts feeding on an infected person and immediately feeds on a susceptible host. This form of transmission does not require virus incubation.

Stages of the disease


Febrile Phase

Patients develop sudden high fever. This acute febrile phase lasts 2-7 days and is usually accompanied by skin flushing, erythema, generalized body pain, myalgia, arthralgia, headache, and retro-orbital pain. Minor hemorrhagic manifestations, such as petechiae and ecchymoses in the skin may occur. Patients, who improve after the initial fever, are considered dengue without warning signs.

Problems that may arise in the febrile phase: dehydration, high fever associated with neurological disorders, and seizures in young children.

Critical Phase

After the fever abates, the patient may experience within the first 3-7 days of illness an increase of capillary permeability parallel with increased hematocrit levels. This marks the beginning of the critical phase with the highest risk of developing plasma leakage with or without hemorrhage, known as severe dengue. Patients who clinically worsen after fever subsides should be monitor for warning signs and hemorrhagic manifestations.

Problems that can occur in the critical phase: shock by plasma extravasation, severe bleeding, and serious organ impairment.

Recovery Phase

Most patients survive the acute phase (which does not exceed 48 to 72 hours), with timely initiation of judicious fluid management and careful monitoring of patient during critical phase, and enter the recovery or convalescent phase. There is a general improvement in the patient: appetite recovers, gastrointestinal symptoms improve, hemodynamic status stabilizes and diuresis increases.

Problems that can occur in the recovery phase are overload (if intravenous fluid therapy has been excessive or has been extended in this period).

Revised Classification of Dengue


The classification recommended by the World Health Organization in 2009. Classification of dengue was revised after the results of the DENCO study, which included nearly 2,000 confirmed cases of dengue in eight countries and two continents. This revision provided two forms of the disease: dengue and severe dengue.

Diagram of revised dengue classification (Spanish available only). Under the revised classification, the level of severity has been separated into dengue, without warning signs and with warning signs, and severe dengue as a practical use during the clinical decision process as to where and how intensively the patient should be observed and treated.

  • Dengue without warning signs: The disease may manifest as a "nonspecific febrile syndrome." A confirmed dengue case in the community the patient belongs is a determinant to suspect the clinical diagnosis of dengue.

  • Dengue warning signs: The patient may present with persistent and severe abdominal pain, persistent vomiting, fluid accumulation, mucosal bleeding, altered mental status, hepatomegaly and progressive increase in hematocrit.

  • Dengue severe: Severe dengue is defined by one or more of the following: (i) shock from plasma leakage, fluid accumulation with respiratory distress, or both, (ii) severe bleeding as evaluated by clinician, or (iii) severe organ involvement; liver: AST or ALT ? 1000; CNS: impaired consciousness; and includes heart and other organs.

Differential Diagnosis


Upon making a diagnosis, clinicians should be aware that some signs and symptoms might be difficult to differentiate from those of other diseases such as malaria, rubella, measles, typhoid fever, meningitis and influenza. Rhinorrhea (runny nose) or nasal congestion does not occur in dengue cases.

Laboratory Diagnosis


The definitive diagnosis of dengue infection is made in the laboratory and is dependent on the detection of specific antibodies in the patient’s serum, detection of viral antigen or viral RNA in serum or tissue, or viral isolation. A blood sample in the acute phase should be taken as soon as possible after the onset of febrile sign. A blood sample from the convalescent phase ideally should be taken 2-3 weeks later.

1. Serological Test:

This can be done by immunoglobulin M (IgM) capture enzyme linked immunosorbent assay (MAC-ELISA), indirect immunoglobulin (G ELISA), hemagglutination -inhibition (HI), complement fixation (CF), neutralization test (NT), or non-structural protein 1 enzyme linked immunosorbent assay (NS1 ELISA). 

2. Viral Isolation

Four viral isolation systems have been used for dengue virus, intracerebral inoculation in mice 1-3 days of age, cultures of mammalian cells (LLC-MK2), intrathoracic inoculation of adult mosquitoes and using mosquito cell cultures.

3. Viral Identification

The method of choice for the detection of the dengue virus is indirect immunofluorescence (IFA): type-specific monoclonal antibodies produced in tissue cultures or ascites fluid of mice and IgG-fluorescein isothiocyanate conjugate.

4. RT-PCR (Reverse Transcription-Polymerase Chain Reaction)

RT-PCR is a rapid, sensitive, simple and reproducible method with appropriate controls. It is used to detect viral RNA in clinical samples from humans and mosquitoes autopsy tissue. RT-PCR is similar to viral isolation with the advantage that problems in the handling, storage and the presence of antibodies do not influence result. However, it should be emphasized that the PCR does not replace viral isolation techniques.

5. Immunohistochemistry

With immunohistochemical, it is possible to detect the virus antigen in a variety of tissues. This method conjugates polyclonal and monoclonal antibodies to an enzyme, such as phosphatases and peroxidases, that then catalyzes a color-producing reaction (stain) that can be analyze.

6. Rapid Tests

The clinical features of dengue are not very specific and therefore require laboratory confirmation.

Accurate and sophisticated methods such as isolation or polymerase chain reaction (RT-PCR) of virus require advanced equipment and infrastructure. Serological tests are widely available and can provide an alternative to support the diagnosis. Primary infections (new) of DENV typically have a stronger and more specific IgM response; subsequent infections (secondary) show a weaker IgM response but a strong IgG response.

These patterns of differentiation of IgM response to infection underscore the need to assess the sensitivity and specificity of tests commercially available, especially for the diagnosis of secondary DENV infections. WHO / TDR and the Pediatric Dengue Vaccine Initiative (PDVI) collaborated to evaluate IgM anti-DENV diagnostic tests commercially available. A network of seven laboratories in Asia and Latin America was established to carry out this collaboration.

The WHO 2009 report, Evaluation of Commercially Available Anti-Dengue Virus Immunoglobulin M Tests, describes the results of an evaluation of nine commercially available IgM anti-DENV tests using a panel of well-characterized specimens with serum from patients with confirmed infections DENV and other infections, and lists potentially confounding conditions.

The NS1 rapid test is a recent introduction on the market that has a high specificity for the diagnosis of dengue (90 to 100%) but low sensitivity (52-62%), indicating a negative result of this test does not rule dengue infection and necessitating an additional test for confirmation of dengue.

7. Clinical tests
  • The complete blood count: including leukocyte and platelet counts.

  • CSF examination provided there is no risk of bleeding.

  • In cases of shock: must determine arterial blood gases, electrolytes, liver and renal function.

  • Thoracic examination: ultrasound, chest radiography and computed tomography.

Treatment


For a disease that is complex in its manifestations, treatment is relatively simple, inexpensive and very effective in saving lives, as long as the correct and timely interventions are made. The key is early identification and understanding of the clinical problems during different stages of the disease, which results in a rational approach to addressing cases and a good clinical response.
 
Good primary care not only reduces the number of unnecessary hospitalizations, but also saves the lives of patients with dengue. Early notification of dengue cases seen in primary and secondary care is crucial for the identification of outbreaks and to initiate timely response.

What to do if you have symptoms of Dengue?

  • Consult your doctor.

  • Watch for signs of serious illness.

  • Do not self-treat; do not use aspirin because it can cause bleeding effect.

  • Do not use antibiotics because a virus causes dengue and antibiotics only attack bacteria.

  • Advances in dengue vaccine

    • 1944 - 1945: The first monovalent (single serotype) were presented in 1944 by Kimura and Hotta and in 1945 by Sabin and Schlesinger.

    • 1963: The first clinical study was conducted in Puerto Rico in 1963 during an outbreak of DEN-3. 1,100 volunteers were vaccinated with an attenuated vaccine strain of DEN-1, showing a 50% reduction of dengue cases in the vaccinated subjects versus controls.

    • 1971: The Armed Forces Epidemiological Board of the United States of America decided to create a cooperative program to develop an attenuated vaccine for the 4 serotypes.

    • The development of a tetravalent vaccine that provides lifelong protection and is affordable is crucial for the prevention and control of dengue.

    • To date, there is no antiviral vaccine for dengue. The attack rate is high and dengue epidemics are explosive. Therefore, once triggered, an epidemic is very difficult to control and the health system is overwhelmed. This highlights the need to develop a vaccine that has the ability to prevent epidemics of this disease.

    • From the efforts made in 1944 to the development of the first monovalent vaccines, we have several vaccine candidates produced by different research groups, government agencies and companies that are in various stages of clinical trials in several countries around the world.

    • The current development of an experimental vaccine appears to advance, however, there are still very complex issues to be clarified. It is necessary that the worldwide scientific community continue research to make a vaccine available, as soon as possible.

    • The introduction of a safe and effective vaccine that protects against dengue will significantly benefit endemic countries. In the next three or four years, a vaccine may be available in the immunization schedules of different countries.

    • A publication in November 2012 on the protection of a tetravalent dengue vaccine (Phase 2b clinical trial) in Thai school children showed an efficiency of 30.2%. Efficacy according to virus serotypes was 55.6% for DENV-1, 9.2% for DENV-2, 75.3% for DENV-3 and 100.0% for DENV-4.
    Last Updated on Monday, 31 March 2014 09:55

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