The yellow fever virus is related to dengue and Zika, transmitted by mosquitoes from monkeys to humans and between humans.


Yellow Fever is endemic in Africa, where Angola is facing its worst outbreak in 30 years ( several thousand suspected cases and a few hundred deaths ). Democratic Republic of Congo, Kenya, and China have reported cases arising from infected travellers from Angola.


It can be difficult to diagnose. After 3-6 days’ incubation, there is fever with headache, muscle pains, nausea, perhaps vomiting - usually improving in a week. ~ 1/7 patients develop jaundice ( hence " yellow fever " ), bleeding and kidney damage - about half of these die.


Confirmation is by lab tests for viruses and antibodies in the blood. There is NO specific antiviral drug or immune treatment.


A licensed, cheap and safe vaccine has been available for 80 years. One dose can give lifelong immunity within 10 days of vaccination for most people, and for almost all within 30 days.


World Health Organization responded much more quickly to this epidemic than with either Ebola or Zika. It does need a permanent emergency committee to respond to each new disease threat - infectious or otherwise.


Already millions of Angolans have been vaccinated ; Democratic Republic of Congo has also started vaccination. The world has an " emergency stockpile " of 11 million doses, held on top of normal supply - already becoming depleted. Production of vaccines must be stepped up, anticipating outbreaks elsewhere in Africa, Latin America or even Asia.


Yellow fever is an " old disease " - in the 19th century it was notorious in the Americas and there were also outbreaks in Europe. More recent outbreaks in Africa have resulted from migration to cities, with mosquitoes adapted to urban life and out of control.


One blessing, and mystery, is that ( so far ) Asia has remained FREE of yellow fever. Maybe Asian strains of Aedes aegypti ( mosquito spreading yellow fever ) are poor transmitters - even though they pass on dengue with ease. Since A. Aegypti is especially rife in India, Myanmar , Cambodia and Thailand, they must be alert to the threat. This mosquito has recent form in spreading disease to new places. Another challenge for WHO .