Mapping the H7N9 avian flu outbreaks
Where are the 104 human cases reported so far and where might the virus go next?
•Declan Butler 24 April 2013
There has been no evidence of sustained human-to-human spread of H7N9 so far. But what if it happened? In what Jeremy Farrar, director of the Oxford University Clinical Research Unit in Ho Chi Minh City, Vietnam, describes as an "extraordinary effort", he and other international researchers including those from China and the WHO, have worked together the past weeks to rapidly analyse airline passenger data for China. The resulting maps and data may give an idea of where the zones of immediate highest risk worldwide might be.
One map supplied to Nature by the researchers shows, they note, that Eastern China — the epicentre of the current the H7N9 outbreak — is one of the world's busiest hubs for airline traffic. "A quarter of the global population outside of China lives within two hours of an airport with a direct flight from the outbreak regions, and 70% if a single connecting flight is included," the researchers explained to Nature.
A flight risk?
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Flight routes from the outbreak regions would quickly carry any human-transmissible virus to huge population centres in Europe, North America, and Asia. (Estimated numbers of people residing within two hours travel time of each destination airport were calculated using gridded population density maps and a dataset of global travel times.) Map supplied by Tatem A, J. , Huang, Z. and Hay, S.I. (2013). Unpublished data.
Other virus vectors?
The novel H7N9 virus has mutations that make it easier for it to spread from birds to humans than it is for H5N1. Proximity between bird and mammal populations could also give the virus opportunities for further adaptation to mammals, including humans. An international team of researchers compiled maps for Nature showing the huge densities of chickens, pigs and humans in many parts of China and throughout Asia. They calculate that 131 million people, 241 million domestic chickens, 47 million domestic ducks, and 22 million pigs live within a 50 kilometre radius of each of the 60 H7N9 human cases that had occurred up to 16 April.
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H7N9 cases, and densities of humans, pigs, chickens and ducks in China and Asia. (Livestock densities are modelled numbers of animals per square kilometre standardised to 2006 national totals. Note different scale for pigs. H7N9 case locations are courtesy of EMPRES, FAO, Rome. Human population from ASIAPOP. Source: Map supplied by Robinson, T.P., Wint, G.R.W., Conchedda, G., Van Boeckel, T.P., Ercoli, V., Palamara, E., Cinardi, G., D’Aietti, L. and Gilbert, M. (2013) Unpublished data.
http://www.nature.com/news/mapping-the- ... ks-1.12863
