Fact – Dengue is a fever that occurs in monsoon months and lasts for one or two months post-monsoon.
Clinical Relevance – If a patient comes with an acute fever in say February or March, one should not think of dengue as a likely cause.
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Fact – Dengue is caused by a virus.
Clinical Relevance – Antibiotics are contraindicated in dengue. Dengue, like most acute viral illnesses, has a self-limiting course.
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Fact – There are four subtypes of dengue virus.
Clinical Relevance – One person can get dengue fever a maximum of four times in her/his lifetime. Immunity for the subtype that causes fever is lifelong.
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Fact – Serum antibodies that rise in response to one subtype protect against other subtypes for a few months.
Clinical Relevance – In any one monsoon, a person will rarely get dengue twice even if more than one subtype is doing the rounds.
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Fact – Severe dengue, a term that has encompasses dengue haemorrhagic fever and dengue shock syndrome occurs mostly in children below 15 years of age who were previously infected and now get infected with a different dengue subtype. This occurs in children who have low antibody titers related to the previous infection. They develop ADE – antibody-dependent enhancement – during the acute second infection. These antibodies cause capillary leak.
Clinical Relevance – When a child presents with dengue it is important to do the dengue IgG test which diagnoses past infection. If IgG is positive in a patient with acute dengue, closer monitoring is mandated.
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Fact – Dengue occurs through bites of infected mosquitoes of the Aedes genus which bite from dawn to dusk.
Clinical Relevance – Bites from the two principal species, Aedes aegypti and Aedes albopictus, can be prevented by suitable long clothing and mosquito repellents. Mosquito nets which are principally used at night are of less relevance, except in infants.
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Fact – Aedes mosquitoes breed in clean water unlike Anopheles mosquitoes that breed in muddy/brackish water.
Clinical Relevance – While malaria incidence goes significantly down with pesticide spraying and cleaning of nallahs and gutters, dengue incidence is less influenced.
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Fact – Aedes mosquitoes typically bite around ankles and neck.
Clinical Relevance – Socks and stoles/mufflers are good clothing to prevent dengue.
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Fact – The Aedes mosquitoes are extremely agile and restless and flit quickly from person to person to complete a meal.
Clinical Relevance – One infected mosquito can cause dengue in multiple persons of a family especially if the family stays in a small area. Thus slum-dwelling families can have multiple persons infected.
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Fact – The incubation period – time from bite to fever – for dengue is 3 to10 days whereas for malaria it is 7 to 30 days.
Clinical Relevance – If a traveller to a mosquito-infested region during Indian monsoons presents with fever within 7 days of entering, you should think of dengue but not malaria.
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Fact – Fever of dengue generally lasts not more than 7 days with a range of 2 to 9 days.
Clinical Relevance – Dengue fever does not feature in the differential diagnosis of prolonged pyrexia.
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Fact – Dengue affects muscles.
Clinical Relevance – Rise in SGOT, which is a muscle enzyme too, is greater than the rise in SGPT, which is a liver enzyme.
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Fact – Extravasation occurs due to antibody-mediated damage to small vessels.
Clinical Relevance – Since significant antibody levels occur after 4th day of fever, signs of leak will only appear 5th day onwards. This is the time we need to check closely for rise in haematocrit, peripheral oedema, tachypnoea due to small pleural effusions, crepitations, and rebound tenderness in lower abdomen caused by ascites. An ultrasound usually confirms extravasation.
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Fact – Extravasation increases if intravascular hydrostatic pressure increases.
Clinical Relevance – A common error made in managing haemodynamically stable patients is giving large amounts of intravenous fluids when Hb and PCV rise. This can easily push patient in florid pulmonary oedema. Remember that this is not the haemoconcentration of dehydration. In fact, if the BP is stable and oral intake is fair, one should stop intravenous fluids at this juncture.
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Fact – Platelet counts continue to fall for one or two days after fever disappears.
Clinical Relevance – Many patients are unnecessarily admitted and given transfusions because of this. If fever has gone and patient is consuming enough orally, assure the patient that even a count of 20000 is not an indication for admission.