Arboviruses (dengue, Zika, chikungunya)

Arboviruses - Mosquito Mayhem

• RNA viruses transmitted by arthropods, primarily Aedes mosquitoes (A. aegypti, A. albopictus).
• Key diseases:
  • Dengue: "Breakbone fever," hemorrhagic complications, thrombocytopenia.
  • Chikungunya: Severe, debilitating polyarthralgia.
  • Zika: Congenital microcephaly, Guillain-Barré syndrome.

⭐ Antibody-Dependent Enhancement (ADE): Prior infection with one dengue serotype increases the risk of severe disease (e.g., Dengue Hemorrhagic Fever) upon infection with a different serotype.

Dengue Fever - The Breakbone Ache

• Virus: Flavivirus; 4 serotypes. Transmitted by Aedes aegypti mosquito.
• Classic Dengue (1st infection):
  • Triad: High fever, retro-orbital pain, severe myalgia/arthralgia.
  • 📌 Mnemonic: Breakbone fever.
• Hemorrhagic Fever (DHF)/Shock Syndrome (DSS):
  • Pathophysiology: Antibody-dependent enhancement (ADE) on 2nd infection with a different serotype.
  • Warning signs: Abdominal pain, mucosal bleeding, plasma leakage.
• Labs: ↓Thrombocytopenia, ↓leukopenia, ↑hemoconcentration.

⭐ Exam Favorite: ADE is key; non-neutralizing antibodies from a prior infection enhance viral uptake by macrophages, causing a cytokine storm.

Zika Virus - The Head Shrinker

• Virus: Flavivirus; enveloped, positive-sense ssRNA.
• Transmission: Primarily Aedes mosquito vector. Also transmitted vertically (transplacental) and through sexual contact.
• Clinical Presentation: Usually asymptomatic or a mild illness. Characterized by low-grade fever, maculopapular rash, and non-purulent conjunctivitis.
• Major Complications:
  • Congenital Zika Syndrome: Maternal infection causes severe fetal defects like microcephaly, thin cerebral cortices, and intracranial calcifications.
  • Guillain-Barré Syndrome: Autoimmune-mediated ascending paralysis post-infection in adults.

⭐ Non-purulent conjunctivitis is a key finding that helps distinguish Zika from Dengue and Chikungunya, where it is less common.

Chikungunya - The Bending Pain

• Virus: Togavirus (an Alphavirus).
• Vector: Aedes mosquitoes, same as Dengue and Zika.
• Hallmark Symptom: Severe, debilitating, symmetric polyarthralgia. The name means 'to become contorted'.
• Clinical: Acute high fever, maculopapular rash, and incapacitating joint pain.
  • Arthralgia can become chronic, lasting months to years.

⭐ Unlike Dengue, significant hemorrhage is rare in Chikungunya; however, severe, chronic arthritis is much more common, representing its primary morbidity.

Differential Dx - Arbovirus Showdown

High‑Yield Points - ⚡ Biggest Takeaways

• All three are RNA viruses transmitted by Aedes mosquitoes.
• Dengue ("break-bone fever") can cause hemorrhagic shock and thrombocytopenia. A key concern is antibody-dependent enhancement (ADE).
• Zika virus is linked to congenital microcephaly in newborns and Guillain-Barré syndrome in adults.
• Chikungunya is characterized by debilitating, often chronic, severe polyarthralgia.
• Clinical overlap is common, making serology or PCR essential for diagnosis.