Dengue Fever Overview

Dengue Fever

• Dengue is caused by a virus belonging to the Flaviviridae family, with four distinct serotypes (DENV-1, DENV-2, DENV-3, and DENV-4). A fifth variant, DENV-5, was discovered in 2013.
• All serotypes grant lifelong immunity to the specific serotype and short-term cross-immunity to other serotypes. However, some genetic variants within serotypes can be more virulent, leading to varying disease severity.
• The dengue virus is spread through the bite of an infected Aedes mosquito, primarily Aedes aegypti and Aedes albopictus.
• The virus undergoes a period of extrinsic incubation within the mosquito, lasting 8-10 days. Once infected, the mosquito remains infectious for life.
• Dengue is most common during the rainy seasons, with a peak incidence observed in July and August.
• In the Philippines, there were over 208,000 dengue cases reported in September 2024, with 7 deaths.
• Global estimates indicate over 200 million dengue cases and 500 dengue-related deaths annually.

Dengue Virus Transmission and Pathogenesis:

• The mosquito's saliva contains anticoagulants, preventing blood clotting and facilitating efficient blood feeding.
• The incubation period for dengue in a human is typically 4-7 days after the bite of an infected mosquito.
• The Antibody-Dependent Enhancement (ADE) phenomenon is a key factor in severe dengue, characterized by pre-existing antibodies from a previous infection failing to neutralize the virus. This results in an increased viral load, potentially leading to dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS).
• ADE occurs when antibodies from a previous infection bind to a different serotype but fail to neutralize it. This complex can attach to Fc receptors on monocytes, leading to more efficient viral entry into monocytes and macrophages.

Dengue Signs and Symptoms:

• Classic Dengue:

  • Fever, often biphasic in nature, lasting 2-7 days.
  • Severe headache.
  • Retro-orbital pain (pain behind the eyes).
  • Nausea and vomiting.
  • Maculopapular or macular rash, often appearing during the convalescent phase and often described as "white islands in a sea of red."
  • Positive Tourniquet test, indicating capillary fragility and potential for bleeding (≥10 petechiae per 2.5 cm²).

• Severe Dengue: Presence of warning signs is crucial for diagnosis and treatment.

  • Plasma Leakage: Increased hematocrit, pleural effusions, ascites, circulatory compromise, and shock.
  • Bleeding: Epistaxis, gingival bleeding, bleeding from injection sites.
  • Organ Involvement: Liver impairment (elevated AST/ALT >/= 1000), acute renal failure, encephalopathy, CNS impairment, and cardiomyopathy.

Dengue Classification and Diagnosis:

• WHO Dengue Case Classification:
  • Probable Dengue: Fever plus two of the following: nausea/vomiting, rash, aches/pains, positive tourniquet test, leukopenia, or any warning signs.
  • Warning Signs: Abdominal pain/tenderness, persistent vomiting, fluid accumulation, mucosal bleeding, lethargy/restlessness, liver enlargement >2 cm, rapid decrease in platelet count with increasing hematocrit.
  • Severe Dengue: Severe plasma leakage, bleeding, organ involvement.
• Specimen Collection: Blood samples are essential for laboratory confirmation, detecting dengue virus RNA, and monitoring platelet and hematocrit levels.

Key Diagnostic Tools:

• Tourniquet Test (Capillary Fragility Test):
  • Evaluates hemorrhagic tendencies.
  • A positive result indicates thrombocytopenia and increased capillary fragility.
  • More likely to be positive during the defervescence phase.

Dengue Hemorrhagic Fever:

• Also known as "Dengue Viral Illness with Warning Signs."
• Characterized by biphasic fever, hemorrhagic manifestations, and warning signs mentioned above.

Management and Prevention:

• Management:
  • Supportive care, fluid replacement, and close monitoring.
  • Early recognition and management of warning signs are essential for preventing complications.
• Prevention:
  • Mosquito control measures: eliminating mosquito breeding grounds, wearing protective clothing, using mosquito repellents.
  • Vaccination: Several dengue vaccines are available, offering protection against various serotypes.

Epidemiology:

• Dengue is a major public health problem, particularly in tropical and subtropical regions.
• Global incidence, morbidity, and mortality are increasing.
• Outbreaks occur seasonally, especially during monsoon or rainy seasons.

This quiz explores the key aspects of dengue fever, including its causes, transmission, and global statistics. Learn about the dengue virus serotypes and their implications for immunity. It also highlights the impact of seasonal changes on dengue incidence and provides insight into its spread through mosquito vectors.