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Diseases & Vaccines / More Vaccine Preventable Diseases / Yellow Fever / Clinical Disease
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CLINICAL DISEASE: YELLOW FEVER
acute phase; remission phase; toxic phase
Yellow fever is a mosquito-borne haemorrhagic disease endemic to the tropical regions of Africa and South America. The incubation period following a bite by an infectious Aedes aegypti mosquito vector is 3 – 6 days before the onset of symptoms. The classical disease progression has three phases.
1. Acute Phase
This is the first phase of the disease lasting for 3 to 4 days and is characterised by non-specific symptoms:
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fever
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malaise
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anorexia
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nausea
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headache
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generalised myalgia
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dizziness
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and vomiting.
Young children may experience febrile seizures. A major physical finding during this phase is congestion of the conjunctivae, gums and face; laboratory findings are leucopoenia and elevated serum transaminase levels which precede the onset of jaundice.
2. Remission Phase
Most patients enter a phase of remission lasting for 48 hours where the fever and symptoms abate and the patient recovers. However, 15% of cases enter a third stage of the disease which can be fatal.
3. Toxic Phase
Where recovery is incomplete, patients enter the toxic phase which is characterised by high fever, severe nausea and vomiting, relative bradycardia, jaundice and haemorrhagic diathesis. There is multiple organ system dysfunction, including the liver, kidneys and cardiovascular system and death usually follows with 7 to 10 days.
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