Clinical features

After an incubation period of three to six days, presentation may vary in severity from non-specific, self-limited symptoms of fever, malaise, photophobia and headache to an illness of sudden onset with fever, vomiting and prostration which may progress to jaundice and haemorrhage (1).

The presentation may be divided into two phases:

• first or acute phase:
• viremia is present (2)
• acute onset of high fever (39 to 40 degrees C) which returns to normal in four to five days
• other clinical features may include arthralgia, myalgia headache, retrobulbar pain, epigastric discomfort, vomiting, suffused conjunctivae and facial flushing
• from the second day there may be relative bradycardia
• most patients improve and their symptoms disappear after 3 to 4 days
• second or toxic phase:
• seen within 24 hours of the initial remission in around 15% of cases
• the patient's condition deteriorates and may develop increasing fever, increasing jaundice and hepatomegaly
• the patient may also develop ecchymoses, haematemesis, melaena and have bleeding mucous membranes
• the patient may become comatose (either as a result of the uraemia or haemorrhagic shock) a few hours before death
• mortality may be as high as 50% with death occurring within 10 to 14 days (3)

For local populations in endemic areas, the overall fatality ratio is about 5%, rising to 20–30% once jaundice and severe symptoms occur.

In nonimmune travellers and migrants, and during epidemics in areas that have low levels of yellow fever activity, the case fatality rate can exceed 50%

Reference:

• (1) Immunisation Against Infectious Disease - "The Green Book". Chapter 35. Yellow fever (July 2013)
• (2) European Centre for Disease Prevention and Control (ECDC). Yellow fever. Factsheet for health professionals
• (3) Markoff L. Yellow fever outbreak in Sudan. N Engl J Med. 2013;368(8):689-91.
• (4) World Health Organization (WHO) 2013. Fact sheet. Yellow fever