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Dengue Fever

Dengue fever, Dengue haemorrhagic fever ( Break bone fever ), Dengue shock syndrome


There is a range of disease according to the severity

Introduction

Dengue Haemorrhagic Fever is a mosquito-borne viral infection endemic in the tropical and sub-tropical regions. The female Ae.aegypti (the most important vector) mosquito is semi-domesticated, preferring to lay its eggs in man-made water containers, resting indoors and feeding in the early morning or late afternoon. There are 4 serotypes of Dengue virus. Dengue usually occurs as epidemics in Sri Lanka following monsoon seasons.

According to data from epidemiology unit of Sri Lanka, the number of total cases recorded for year 2009 is 32713. Most affected district was Kandy. Colombo, Gampaha and Kaluthara districts which have been susceptible in the past have also recorded a high rate of infection and deaths.

Causative agents

Dengue virus; There are 4 serotypes of the single-stranded RNA virus (flaviviridae).

Pathogenesis / Action in the body

Patients become infected once bitten by mosquitos. The virus passes to lymph nodes and replicates which is followed by spread to the circulation and other tissues. It is thought that infection with a secondary serotype is what leads to severe haemorrhagic disease.4

Symptoms and signs

Disease varies in severity

  • Incubation period is 2-7 days.
  • All haemorrhagic fever syndromes begin with abrupt onset of fever (39.5–41ºC) and myalgia.
  • Fever is often biphasic with two peaks.
  • Fever is associated with frontal or retro-orbital headache lasting 1–7 days, accompanied by generalised macular, blanching rash.
  • Initial rash usually fades after 1–2 days.
  • Symptoms regress for a day or two then rash reappears in maculopapular, morbilliform pattern, sparing palms and soles of feet. Fever recurs but not as high. There may be desquamation.
  • DF cases experience severe bony and myalgic pain in legs, joints and lower back which may last for weeks (hence breakbone fever).
  • Nausea, vomiting, cutaneous hyperaesthesia, taste disturbance and anorexia are common.
  • Abdominal pain may occur and if severe suggests DHF pattern.

The signs of dengue fever/ Dengue haemorrhagic fever are

  • High fever, rash, hypotension and narrow pulse pressure, poor capillary refill.
  • There may be hepatomegaly and lymphadenopathy.
  • A tourniquet placed on an arm may induce petechiae in early DHF cases. DHF sufferers exhibit a bleeding tendency as evidenced by petechiae, purpura, epistaxis, gum bleeding, GI haemorrhage and menorrhagia. There may be pleural effusion, ascites and pericarditis due to plasma leakage.
  • Petechiae are best visualised in the axillae.
  • Flushing of head and neck.
  • Tender muscles on palpation.
  • Periorbital oedema and proteinuria may be present.
  • Maculopathy and retinal haemorrhages may also occur.5
  • DSS pattern cases progress through DHF until profound shock due to severe hypotension is present.
  • CNS involvement e.g. encephalopathy, coma, convulsions.

Complications

Dengue can cause death

Investigations

  • FBC - low platelets and high packed cell volume if haemoconcentrated. Usually white cell count will fall
  • Infection may be confirmed by isolation of virus in serum and detection of IgM and IgG antibodies for Dengue by ELISA, monoclonal antibody or haemagglutination.7
  • Molecular diagnostic methods such as reverse-transcriptase-PCR are increasingly being used.
  • Chest X-ray may show pleural effusion.8

Management

  • Bed rest
  • Nutritious diet and lot of liquids, But avoid red and brown foods and drinks like coffee, chocolate, grapes etc  as it may misinterpret vomiting as blood stained vomitus.
  • Fever control with paracetamol, tepid sponging and fans. Aspirin should be avoided.
  • Need to seek advice from a qualified medical practitioner if fever lasts for more than 2 days
  • Hospital managemnt includes intravenous fluid resuscitation with close monitoring. Haemorrhage and shock will require Fresh Frozen Plasma, platelets and blood. Intensive management with inotropes of the shock syndrome may be required in severe DHF/DSS cases.

Prevention and Promotion

  • Vaccines are being researched
  • Anti-mosquito public health measures such as reducing breeding sites ( flower pots, fish tanks,tires, coconut shells, tins, water collecting plants, gutters which can collect water) and good sewage management
  • Insecticides to destroy the larvae
  • Mosquito nets can be used during day time as the Aedes mosquitoes is day-biting.
  • Mosquita repellents
  • There is a bacteria called Bacillus thuringiensis which destroy the mosquito larvea
 

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