25 March 2013

YELLOW FEVER: Still with us after all these years


Most of us associate yellow fever with the nuisance of requiring the vaccine in order to enter and work in certain countries.  I personally have never seen a case (at least one that I recognized).  Yet the disease remains.  Once world-wide in distribution, yellow fever is now confined to tropical South America and Sub-Saharan Africa.  In late 2012 a small epidemic occurred in the Darfur region of Sudan, resulting in 849 cases and 171 deaths.  WHO estimates that some 200,000 cases occur each year in endemic countries, causing 30,000 deaths.  90% of these cases occur in Sub-Saharan Africa. 
Yellow fever is the most virulent virus in the flavivirus group, which includes dengue, West Nile and Japanese encephalitis.  All flaviviruses are arthropod borne.  Yellow fever is transmitted by Aedes mosquitos.  The initial symptoms of disease are non-specific, and very similar to those of dengue fever.  They include fever, severe muscle pain, headache, abdominal pain and nausea and vomiting.  Most patients recover uneventfully after 3-6 days.  However 15 to 25 percent enter a more toxic second phase with acute, fulminant hepatitis, jaundice (the yellow in yellow fever), generalized bleeding, shock, and death in approximately 50% of cases. Diagnosis is confirmed by virus specific antigen (ELISA), or antibody (PCR) testing. Treatment is supportive, restricted to management of the severe shock and bleeding disorder. 
The currently used vaccine is very effective.  WHO requires revaccination every 10 years, however the protective effect of a single does is probably life-long.  Side reactions, though very uncommon, can be severe. Vaccination should therefore be considered only for those who travel to countries where the disease is endemic.   Be aware that up to date vaccination (within 10 years) is a requirement for entry into all countries where yellow fever is endemic, including tropical South America and Sub-Saharan Africa.  See the CDC recommendations for details.
Ref:  Markoff, L.: Yellow Fever Outbreak in Sudan.  NEJM 2013: 368: 689-691
Submitted by Roger Boe MD.

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