Drivers for emerging issues in animal and plant health

Richardson, Jane; Lockhart, Caryl; Pongolini, Stefano; Karesh, William B.; Baylis, Matthew; Goldberg, Tony; Slingenbergh, Jan; Gale, Paul; Venturini, Tommaso; Catchpole, Mike; de Balogh, Katinka; Pautasso, Marco; Broglia, Alessandro; Berthe, Franck; Schans, Jan; Poppy, Guy

Emerging methods in epidemiology have the potential to inform a comprehensive assessment of how pathogens might move from natural settings into agricultural areas and human habitations and vice versa pathogen spill over from agricultural areas into natural or semi-natural environments (Freer-Smith and Webber, 2015) . The search for new disease transmission pathways could be independent of the pathogens themselves, which may be unknown, lurking undiscovered in reservoirs, or not yet even evolved. An organism in its native environment might not be pathogenic, but can become so when introduced into a new setting; as shown, for example, by Hymenoscyphus fraxineus, an Ascomycete fungus causing ash dieback, a chronic fungal disease of ash trees (Fraxinus excelsior) in Europe characterised by leaf loss and crown dieback in infected trees, subsequent to its introduction in Poland at the beginning of the 1990s. The fungus appears to live endophytically without causing symptoms on Fraxinus mandshurica commonly called Manchurian ash, a medium to large deciduous tree, native to wooded slopes and open valleys of northeast Asia and Japan. Moreover, multiple pathogens traverse common transmission pathways, such that disrupting these pathways would have wide-ranging health impacts beyond individual diseases. The expected benefit would be at a level not fully attainable by any other approaches. A caveat to this would be that these pathways could also be important for microorganisms conferring health benefits, such as improving nutrient/vitamin availability or beneficial immune modulatory effects. Taking the example of zoonotic risk, many undiscovered transmission pathways involve human cultural practices that bring people into contact with reservoirs or vectors at times in places that are especially suitable for subsequent human-to-human transmission. Some pathways may not presently be traversed by any known pathogens, making them invisible to traditional epidemiological approaches. To discover them would require a re-focusing of efforts by epidemiologists and social scientists working together to better understand pathways of transmission among plants, animals and humans.