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dengue_fever

dengue fever

introduction

  • flaviviral mosquito-borne (Aedes albopictus and A. aegypti) illness of the tropics including northern Queensland
  • these mosquitoes usually live between the latitudes of 35° North and 35° South below an elevation of 1,000 metres (although in Mexico and Sth American tropics have been found up 2200m but the mosquitoes are rare higher than 1700m) where average winter isotherms are above 10degC
  • 50–100 million people infected yearly globally and this is increasing
  • virus has four different types
  • infection with one type usually gives lifelong immunity to that type, but only short-term immunity to the others.
  • there is no vaccine or treatment but most resolve spontaneously
  • dengue can also be transmitted via infected blood products and through organ donation
  • mortality of symptomatic cases overall is 1-6% untreated, and < 1% if treated

clinical features of uncomplicated dengue

  • short incubation period 4-7 days
  • 80% are asymptomatic
  • children may have a URTI-like illness or a gastro-like illness but then are more at risk of complications
  • fever often over 40degC, classically biphasic but is variable
  • headache - typically retro-orbital
  • muscle and joint pains hence its other name “break-bone fever”
  • characteristic maculopapular rash in 50-80% of those with symptoms
    • initially just flushed skin appearance on day 1-2
    • then on days 4-7 similar to measles rash +/- petechiae +/- mild bleeding from mouth/nose
  • metabolic acidosis

host risk factors for severe disease

  • severe disease is more common in babies and young children, and in contrast to many other infections it is more common in children that are relatively well nourished
  • can be life-threatening in people with chronic diseases such as diabetes and asthma.
  • G6PD deficiency
  • certain gene polymorphisms involving genes coding for TNFα, mannan-binding lectin, CTLA4, TGFβ, DC-SIGN, and particular forms of human leukocyte antigen.
  • subsequent infection with a different type increases the risk of severe complications

severe disease

critical phase

  • occurs in 5% of symptomatic patients and follows resolution of high fever and typically lasts 1-2 days
  • severe disease is marked by two problems:
    • dysfunction of endothelium
    • disordered blood clotting
  • dengue shock syndrome and dengue haemorrhagic fever
  • severe bleeding from GIT
  • pleural effusions and ascites may develop from capillary leakage
  • organ failure and death in up to 26% who develop severe disease
  • this is followed by a recovery phase lasting 2-3 days:
    • fluid is resorbed
    • striking recovery
    • severe pruritis
    • slow heart rate
    • risk of fluid overload, cerebral oedema with seizures and reduced conscious state

other rare complications

  • encephalitis
  • liver failure
  • transverse myelitis
  • Guillain-Barré syndrome
  • myocarditis

DDx

Dx

  • clinical
  • tourniquet test - count number of petechiae distally after 5 minutes application of BP cuff
  • PCR from blood
  • serology

Rx

dengue_fever.txt · Last modified: 2016/01/14 10:48 by gary1