High risk landscapes of Japanese encephalitis virus outbreaks in India converge on wetlands, rainfed agriculture, wild Ardeidae, and domestic pigs

Japanese encephalitis constitutes a significant burden of disease across Asia, particularly in India, with high mortality in children. This zoonotic mosquito-borne disease is caused by the Flavivirus, Japanese encephalitis virus (JEV), and circulates in wild ardeid bird and domestic pig reservoirs both of which generate sufficiently high viremias to infect vector mosquitoes, which can then subsequently infect humans. The landscapes of these hosts, particularly in the context of anthropogenic ecotones and resulting wildlife-livestock interfaces, are poorly understood and thus significant knowledge gaps in the epidemiology and infection ecology of JEV persist, which impede optimal control and prevention of outbreaks. The current study investigated the landscape epidemiology of JEV outbreaks in India over the period 2010 to 2020 based on national human disease surveillance data. Outbreaks were modelled as an inhomogeneous Poisson point process. Outbreak risk was strongly associated with the habitat suitability of ardeid birds and pig density, and shared landscapes between fragmented rainfed agriculture and both river and freshwater marsh wetlands. Moreover, risk scaled with Ardeidae habitat suitability, but was consistent across scale with respect to pig density and rainfed agriculture-wetland mosaics. The results from this work provide a more complete understanding of the landscape epidemiology and infection ecology of JEV in India and suggest important priorities for control and prevention across fragmented terrain comprised of wildlife-livestock interface that favours spillover to humans.

Landscape epidemiology of ash dieback

Ash dieback caused by Hymenoscyphus fraxineus, an invasive alien pathogen, has been severely damaging European ash populations. Nevertheless, a large range of disease severities was observed at the landscape scale in the field. Several studies suggested that environment, such as climate, site conditions or local tree cover strongly affects ash dieback. We characterized the landscape epidemiology of the disease at two stages of the invasion process with spatio-temporal models using Bayesian models fitted by Integrated Nested Laplace Approximation (INLA). We first analyzed the effect of landscape features on the disease arrival and establishment stage at the scale of a village in NE France in 2012, 2 years after first report of the disease in the area and then, on the disease development stage in 2016-18. Landscape features had little impact on the disease at the establishment stage but strongly determined it further development. The local fragmentation of the tree cover was the most important factor with trees isolated or in hedges in agricultural settings far less affected then trees in forest environment. We showed that they were subjected to different microclimate with higher crown temperatures unfavorable to the pathogen development. Furthermore, host density was important for disease development with ash at low density far less affected by ash dieback. Presence of ashes in the vicinity affected local disease severity up to several hundred meters. These results may help to develop management strategy for the disease.

Mysterious and Mortiferous Clouds: The Climate Cooling and Disease Burden of Late Antiquity

What influence did climate have on disease in Late Antiquity? Natural archives of pre-instrumental temperature indicate significant summer cooling throughout the period. The coolest stretch spanned the 6th and 7th c., and corresponds startlingly to the appearance of the Justinianic Plague in the Mediterranean region. Drawing on principles from landscape epidemiology, this paper marries textual evidence for disease with palaeoclimatic data, in order to understand how gradual and dramatic climatic change, the 535–50 downturn especially, may have altered the pathogenic burden carried in Late Antiquity. Particular attention is paid to the Justinianic Plague, but the potential impacts of a changing climate on malaria and non-yersinial, non-plague, epidemics are not overlooked.