Arthropod-born Viral Diseases

 

• Background

  • Viral infections spread by arthropods, usually mosquitoes or ticks. The four described here are transmitted by the Aedes aegypti mosquito.
  • As with most viral infections, treatment is primarily supportive.
  • Other arborviruses, not discussed here, include Crimean-Congo Haemorrhagic fever, West nile virus, and tick-borne encephalitis.

• Dengue fever

  Geography and incubation

  • Southeast Asia, Central and South America.
  • 4-8 days incubation usually (but can be up to 2 weeks).

  Presentation

  • Fever
  • Arthralgia and myalgia ('breakbone fever').
  • Rash (flushing/petechial).
  • Headache, retroorbital pain, red eye.
  • Dengue haemorrhagic fever: haemorrhagic symptoms, PLT <100, and signs of plasma leak (e.g. ↑haematocrit, effusions).
  • Dengue shock syndrome: SPB <90 mmHg or pulse pressure <20 mmHg.

  Investigations

  • FBC: ↓PLT, ↓WBC.
  • Diagnose with serum PCR initially or IgM ELISA (>5 days).

  Management

  Supportive, but avoid NSAIDs as they may exacerbate haemorrhage.

• Chikungunya

  Geography and incubation

  • South Asia, Africa, and Americas.
  • 2-4 days incubation usually (but can be up to 2 weeks).

  Presentation

  • Sudden onset high fever, and usually sudden cessation after ~10 days.
  • Severe arthralgia and myalgia. In 25%, arthralgia may persist for months-years.
  • Rash
  • Uveitis

  Investigations

  Serum PCR initially or IgM ELISA (>5 days).

  Management

  Supportive.

• Zika virus

  Geography and incubation

  • Caribbean and Latin America.
  • 3-14 days incubation.
  • As well as mosquito bites, can be sexually transmitted.

  Presentation

  Viral syndrome (usually mild):

  • Maculopapular rash (98%), often itchy.
  • Systemic: fever and arthralgia (60%).
  • Conjunctivitis (40%).

  Complications:

  • Congenital: microcephaly (7%) and other abnormalities.
  • Guillain‐Barré syndrome.

  Investigations

  Serum PCR initially or IgM ELISA (>5 days).

  Prevention of congenital Zika

  • Women to postpone pregnancy for 2 months after last possible exposure.
  • Pregnant women to avoid travel to high risk areas.
  • Male partners of pregnant women who travel to high risk areas to use condoms for 6 months after return, even if no symptoms.

  Management

  Supportive.

• Yellow fever

  Geography and incubation

  • South America and Africa.
  • 3-6 days incubation.

  Presentation

  • Usually mild, non-specific syndrome of fever, headache, myalgia, and low back pain.
  • After 3-4 days, most patients go into remission.
  • 15% of patients will relapse after 2 days in remission, and enter a 'period of intoxication', featuring fever, vomiting, epigastric pain, jaundice, haemorrhage, and varying degree of multiorgan failure. This stage carries 25% mortality rate.

  Investigations

  • IgM ELISA for diagnosis.
  • Other bloods: ↓neutrophils, ↑LFTs (AST > ALT), clotting and platelet abnormalities in haemorrhagic fever.

  Management

  Supportive.