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Aedes aegypti carries Dengue virus, Yellow fever and Chikungunya. There are two forms - Dengue fever in first exposure and the more serious Dengue haemorrhagic fever in a second exposure to a different serotype

About

• Dengue fever is due to viral infection (flavivirus)
• Spread by either the Ae. aegypti or Ae. albopictus mosquitos
• Predominantly affects children in endemic areas

Spread

• Viral haemorrhagic fever spread by the mosquito (Aedes aegypti)
• DHF/DSS is endemic in Asia and Pacific and Cuba and the Americas
• Aedes aegypti mosquitos bite just after dawn and just before sunset.
• The incubation period of less than 5-6 days is useful.

Aetiology

• Severe disease requires the presence of dengue antibodies to previous infection
• There are several serotypes Dengue virus 1,2,3,4 which are important with a second infection
• For this reason, a person can be infected with a dengue virus as many as four times in his or her lifetime.
• Cross reactivity at the T cell level leads to the release of cytokines, TNF and interferon-gamma
• There is an increased vascular permeability and shock

Clinical Assessment: Presumptive diagnosis

• Live in or travel to endemic area + Acute febrile illness
• Plus two out of
  • Nausea and vomiting
  • Rash often erythematous
  • Aches and pains (Retro-orbital pain worsened by eye movement, joint pains, headache)
  • Warning signs
    • Severe abdominal pain or tenderness
    • Persistent vomiting
    • Mucosal bleed
    • Liver enlargement > 2 cm
    • Clinical fluid accumulation
    • Lethargy restlessness
    • Increase in HCT with fall in platelets
  • Positive tourniquet test
  • Leucopenia
• Symptoms most severe from day 1-5 then they settle down however in a small number the critical period begins with the resolution of the fever and lasts for 24–48 hours. During this period, some patients may rapidly deteriorate

Dengue haemorrhagic fever/Dengue shock syndrome - Reinfection

• Reinfection by a different serotype causes Dengue Haemorrhagic shock
• Bleeding - petechiae, gastrointestinal, shock
• Restlessness, lethargy, platelets < 100 x10⁹/L
• Severe - hypotension, low pulse pressure, cyanosis
• Mortality in a good centre is 1%

Those at risks of DHF/DSS

• Young white, females, well fed
• Mainly affects children under 12 years old
• Females > Males
• Whites > Blacks
• Well-fed > Malnourished
• Serotype 1 > Serotype 2 worse than Serotype 4 > Serotype 2
• Serotype 2 most dangerous

Differential

• Always consider malaria in the differential, though there is classically no rash with malaria.

Investigations

• FBC : Low WCC Low platelets
• Haematocrit high with DHF as haemoconcentrated
• Serology : ↑ x4 IgG antibody titre
• Dengue virus RNA PCR

Prevention

• A Dengue vaccine is now available for U.S. territories and freely associated states.
• The vaccine is approved for use in children aged 9 to 16 years with laboratory-confirmed previous dengue virus infection and living in areas where dengue is endemic (common).

Management (There is no specific treatment for dengue.)

• Who to admit
  • No need to admit those with no warning signs: manage as outpatient. However, do tell them when to return. Teach them about warning signs and their timing, and the critical period that follows the resolution of fever. Once seen and assessed advise rest as much as possible.
  • Take Acetaminophen/Paracetamol to control fever and relieve pain. Avoid aspirin or ibuprofen. Drink plenty of fluids to stay hydrated. Drink water or drinks with added electrolytes. Educate that Symptoms of dengue can become severe within a few hours.
  • Severe dengue is a medical emergency. Symptoms suggesting immediate healthcare assessment are abdominal pain, tenderness, Vomiting (> 3/24 hours), bleeding from the nose or gums, vomiting blood, or blood in the stool, Feeling tired, restless, or irritable
  • Admit those with presumptive diagnosis and warning signs
  • Admit those with presumptive diagnosis and Pregnancy, Infancy, Diabetes, Old age, social issues, renal failure
  • Admit those with Severe plasma leakage, fluid accumulation, respiratory distress, Severe bleeding, severe organ impairment
• Treatment
  • IV fluids (N-Saline) are not always necessary. First, check if the patient can take fluids orally. Use only the minimum amount of IV fluid to keep the patient well-perfused. Decrease IV fluid rate as haemodynamic status improves or urine output increases
  • Platelet transfusion if any active bleeding or if platelets drop to < 10 x 10⁹/L. Avoid any antiplatelet drugs.
  • Monitor I/O and NEWS and haematocrit levels closely. I/O should be measured every 8-12 hrs and NEWS every 4 hours. Haematocrit every 6–12 hours at minimum during the critical period.
  • Look for and manage early shock. Early shock (also known ascompensated or normotensive shock) is characterized by narrowingpulse pressure (systolic minus diastolic BP approaching 20 mmHg),increasing heart rate, and delayed capillary refill or cool extremities.
  • Administer colloids (Albumin) for refractory shock. Those who do not respond to 2–3 boluses of isotonic saline should be given colloids instead of more saline.
  • Give Packed RBC's or whole blood for clinically significant bleeding. If haematocrit is dropping with unstable vital signs or significant bleeding is apparent, immediately transfuse blood
  • Capillary leak syndrome: can happen even with normal platelets with third space shift of fluid causing pleural and pericardial effusion, mild ascites, gallbladder wall oedema with pain, mild generalized oedema. All effusions and gall bladder oedema resolve spontaneously after day 7
  • Generally supportive for most as mortality less than 1%. Avoid antiplatelet due to bleeding risk with thrombocytopenia. No role for antivirals or steroids
  • Eradication of mosquito breeding areas indoors and outdoors measures and vaccination

References

• Dengue CDC Cheat Sheet
• Dengue CDC