By Anne Gulland, 23 AUGUST 2018.
The 2016-17 yellow fever outbreak was the largest in Brazil for more than 100 years, spreading across 10 states. Official figures put the number of those infected at 700 but the figure is likely to be much larger.
Yellow fever is transmitted is transmitted in two ways: either through forest dwelling or city dwelling mosquitoes and primates, which are thought to be the animal reservoir of the disease.
Most outbreaks of yellow fever in Brazil have been traced back to the forests but there were fears that the scale of the most recent outbreak meant that it was down to urban transmission, increasing the likelihood of dangerous outbreaks in the megacities of Sao Paulo and Rio de Janeiro, where vaccination coverage is lower.
However, a team of researchers from Oxford University and Brazilian research institute Fiocruz in collaboration with KRISP and other academic organizations, used genomic data and geospatial mapping to work out where the disease came from and traced it back to forest-dwelling primates.
This transmission cycle grew unnoticed during 2016, before spilling over into human populations in early 2017, researchers say.
Further analyses confirmed that 85 per cent of both human and primate yellow fever cases were male and aged between 35-54 years old – researchers says that this is a tell-tale sign of forest transmission.
An effective yellow fever vaccine has been developed but it is in short supply around the world. Knowing exactly who needs vaccinations would help manage the disease better, researchers say.
Oliver Pybus, professor of evolution and infectious disease in Oxford’s department of zoology, said: "Yellow fever virus has affected humanity for hundreds of years. It comes in waves from an animal reservoir, so we may never completely eliminate it."
"The problem is that we don’t understand enough yet about the complex behaviour of the virus in animal populations. We need this information to control future outbreaks –to vaccinate the right people, in the right place, at the right time."
Dr Nuno Faria, research fellow in the department of zoology at Oxford, called for more funding for research.
He said: "Despite being one of the most important pathogens in human history, yellow fever research has been under-funded compared to other pathogens so new techniques could bring fresh insights.
Crucially, using a combination of genomic and epidemiological approaches we are now starting to understand the hidden dynamics of how the virus jumped from animal populations to people over space and time."
News date: 2018-08-23
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