Factors associated with resurgence of
Dengue epidemics:

1. Unprecedented growth of human population
2. Unplanned and uncontrolled urbanization
3. Inadequate waste management and water supply.
4. Increased distribution and densities of vector mosquitoes Lack of effective mosquito control measures
5. Increased movement and spread of dengue virus.

Transmission:
Female aedes mosquito gets infected with Dengue virus after sucking blood from a person during viremic (acute febrile illness) phase. After an extrinsic incubation period of 8-10 days, infected mosquito transmits infection by biting and injecting infected salivary fluid into the wound of another person. After an incubation period of 3-14 days (4-6 days average), there is sudden onset of disease with fever, anorexia, malaise, headache, nausea, vomiting and rash etc. Viremia starts just before the onset of symptoms and persists for 5-6 days after the onset of illness. Infected female mosquito is capable of vertical transmission of Dengue virus to its next generation, important for virus maintenance but not for epidemics.

Pathogenesis:
It is not fully understood. It is hypothesized that there is enhancement of virus multiplication in macrophages by heterotypic antibodies which were formed during previous dengue infection.


Two pathophysiologic changes occur predominantly:

1. Increased vascular permeability causing selective plasma leakage (pleural, peritoneal) and hypovolemia.
2. Abnormal hemostasis resulting from vasculopathy and coagulopathy with thrombocytopenia causing hemorrhagic manifestations.

One study from Vietnam proposed that endothelial size dependent sieving mechanism for plasma proteins is at least primarily retained whereas selective restriction based on negative charge is impaired. Role of anion glycosaminoglycan (GAG) in pathogenesis of vascular leak was suggested. Study from Germany proposed that there may be turbulence of antioxidant system in response and / or consequence of viral inflammatory process. A study from Vietnam suggested that over production of both proinflammatory cytokines (Interferon and Tumor necrosis factor - a) and anti-inflammatory cytokines (IL-10, 6) may play a role in pathogenesis of DHF/DHS.

Pathogenesis of Dengue: table 1


Clinical presentation: Table 2



Undifferentiated fever:
When there is dengue infection for the first time (primary Dengue infection). It presents like a simple viral fever especially in infants, children or in some adults. Maculopapular rash may or may not be present. Dengue fever: Most commonly seen in older children and adults. Presents as acute biphasic fever with myalgia, arthralgia (Break bone fever), headache, rash, leukopenia and occasionally with unusual hemorrhage.

Dengue hemorrhagic fever:
Children less than 15 years are the most common victims. It presents with acute onset of fever with nonspecific constitutional symptoms and signs of hemorrhagic diathesis, which may progress to fatal shock (Dengue shock syndrome, DSS).