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Vaccination Targeting

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    Posted: August 24 2018 at 1:32am
Yellow fever virus detective work could help target vaccination campaigns

Genomic sequencing of a recent yellow fever outbreak in Brazil has traced it back to its source.

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, 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.”

Key facts | Yellow fever
Color enhanced transmission electron micrograph (TEM) of Yellow Fever Viruses
Colour-enhanced transmission electron micrograph of Yellow Fever Viruses credit: Rex

Yellow fever is an acute viral haemorrhagic disease transmitted by infected mosquitoes. The "yellow" in the name refers to the jaundice that affects some patients

Symptoms include fever, headache, jaundice, muscle pain, nausea, vomiting and fatigue

A small proportion of patients who contract the virus develop severe symptoms and approximately half of those die within seven to ten days

Since the launch of the Yellow Fever Initiative in 2006, significant progress in combating the disease has been made in West Africa and more than 105 million people have been vaccinated in mass campaigns

Yellow fever is prevented by an extremely effective vaccine, which is safe and affordable. A single dose of yellow fever vaccine which gives life-long protection against the disease

Good supportive treatment in hospitals improves survival rates. There is currently no specific anti-viral drug for yellow fever

Absence of proof is not proof of absence.
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