An evaluation of the landscape structure and La Niña climatic anomalies associated with Japanese encephalitis virus outbreaks reported in Australian piggeries in 2022
The widespread activity of Japanese encephalitis virus (JEV) reported in previously unaffected regions of eastern and southern Australia in 2022 represents the most significant local arbovirus emergency in almost 50 years. Japanese encephalitis virus is transmitted by mosquitoes and maintained in wild ardeid birds and amplified in pigs, the latter of which suffer significant reproductive losses as a result of infection. The landscape epidemiology of JEV in mainland Australia is almost entirely unknown, particularly in the eastern and southern parts of the country where the virus has not been previously documented. Although other areas with endemic JEV circulation in the Indo-Pacific region have demonstrated the importance of wild waterbird-livestock interface in agricultural-wetland mosaics, no such investigation has yet determined the composition and configuration of pathogenic landscapes for Australia. Moreover, the recent emergence in Australia has followed substantial precipitation and temperature anomalies associated with the La Niña phase of the El Niño Southern Oscillation. This study investigated the landscape epidemiology of JEV outbreaks in Australian piggeries reported between January and April of 2022 to determine the influence of ardeid habitat suitability, hydrogeography, hydrology, land cover and La Niña-associated climate anomalies. Outbreaks of JEV in domestic pigs were associated with intermediate ardeid species richness, cultivated land and grassland fragmentation, waterway proximity, temporary wetlands, and hydrological flow accumulation. This study has identified the composition and configuration of landscape features that were associated with piggery outbreaks reported in 2022 in Australia. Although preliminary, these findings can inform actionable strategies for the development of new One Health JEV surveillance specific to the needs of Australia.
Michael G. Walsh, Cameron Webb, Victoria Brookes. An evaluation of the landscape structure and La Niña climatic anomalies associated with Japanese encephalitis virus outbreaks reported in Australian piggeries in 2022. One Health, 16, 2023. https://doi.org/10.1016/j.onehlt.2023.100566.
A biogeographical description of the wild waterbird species associated with high-risk landscapes of Japanese encephalitis virus in India
Wild reservoirs of Japanese encephalitis virus are under-studied globally, which presents critical knowledge gaps for JEV epidemiology and infection ecology despite decades of received wisdom regarding this high-impact mosquito-borne virus. As a result, ardeid birds, generally understood to be the primary reservoirs for JEV, as well as other waterbirds occupying landscapes at high risk for spillover to humans, are frequently ignored by current surveillance mechanisms and infrastructure. This is particularly true in India, which experiences a high annual burden of human outbreaks. Incorporating wild reservoirs into surveillance of human and livestock populations is therefore essential but will first require a data-driven approach to target individual host species. The current study sought to identify preliminary waterbird target species for JEV surveillance development based on species’ distributions in high-risk landscapes. Twenty-one target species were identified after adjusting species presence and abundance for the biotic constraints of sympatry. Furthermore, ardeid bird species richness demonstrated a strong non-linear association with the distribution of human JEV outbreaks, which suggested areas with the highest ardeid species richness corresponded to low JEV outbreak risk. No association was identified between JEV outbreaks and anatid or rallid richness. The lack of association between Anatidae and Rallidae family-level diversity and JEV outbreak risk notwithstanding, this study did identify several individual species among these two bird families in high-risk landscapes. The findings from this work provide the first data-driven evidence base to inform wildlife sampling for the monitoring of JEV circulation in outbreak hotspots in India and thus identify good preliminary targets for the development of One Health JEV surveillance.
A biogeographical description of the wild waterbird species associated with high-risk landscapes of Japanese encephalitis virus in India. Michael G. Walsh, Amrita Pattanaik, Navya Vyas, Deepak Saxena, Cameron Webb, Shailendra Sawleshwarkar, Chiranjay Mukhopadhyay. Transboundary and Emerging Diseases, 2022; https://doi.org/10.1111/tbed.14656
High-risk landscapes of Japanese encephalitis virus outbreaks in India converge on wetlands, rain-fed agriculture, wild Ardeidae, and domestic pigs and chickens
Background: Japanese encephalitis virus (JEV) is a zoonotic mosquito-borne virus that causes a significant burden of disease across Asia, particularly in India, with high mortality in children. JEV circulates in wild ardeid birds and domestic pig reservoirs, both of which generate sufficiently high viraemias 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 of JEV persist. This study sought to investigate the landscape epidemiology of JEV outbreaks in India over the period 2010–2020 to determine the influence of shared wetland and rain-fed agricultural landscapes and animal hosts on outbreak risk.
Methods: Using surveillance data from India’s National Centre for Disease Control Integrated Disease Surveillance Programme, JEV outbreaks were modelled as an inhomogeneous Poisson point process and externally validated against independently sourced data.
Results: Outbreak risk was strongly associated with the habitat suitability of ardeid birds, both pig and chicken density, and the shared landscapes between fragmented rain-fed agriculture and both river and freshwater marsh wetlands.
Conclusion: The results from this work provide the most complete understanding of the landscape epidemiology of JEV in India to date and suggest important One Health priorities for control and prevention across fragmented terrain comprising a wildlife–livestock interface that favours spillover to humans.
High-risk landscapes of Japanese encephalitis virus outbreaks in India converge on wetlands, rain-fed agriculture, wild Ardeidae, and domestic pigs and chickens. Michael G Walsh, Amrita Pattanaik, Navya Vyas, Deepak Saxena, Cameron Webb, Shailendra Sawleshwarkar, Chiranjay Mukhopadhyay. International Journal of Epidemiology, 2022; https://doi.org/10.1093/ije/dyac050
Low mammalian species richness is associated with Kyasanur Forest disease outbreak risk in deforested landscapes in the Western Ghats, India
Kyasanur forest disease virus (KFDV) is a rapidly expanding tick-borne zoonotic virus with natural foci in the forested region of the Western Ghats of South India. The Western Ghats is one of the world's most important biodiversity hotspots and, like many such areas of high biodiversity, is under significant pressure from anthropogenic landscape change. The current study sought to quantify mammalian species richness using ensemble models of the distributions of a sample of species extant in the Western Ghats and to explore its association with KFDV outbreaks, as well as the modifying effects of deforestation on this association. Species richness was quantified as a composite of individual species' distributions, as derived from ensembles of boosted regression tree, random forest, and generalised additive models. Species richness was further adjusted for the potential biotic constraints of sympatric species. Both species richness and forest loss demonstrated strong positive associations with KFDV outbreaks, however forest loss substantially modified the association between species richness and outbreaks. High species richness was associated with increased KFDV risk but only in areas of low forest loss. In contrast, lower species richness was associated with increased KFDV risk in areas of greater forest loss. This relationship persisted when species richness was adjusted for biotic constraints at the taluk-level. In addition, the taluk-level species abundances of three monkey species (Macaca radiata, Semnopithecus hypoleucus, and Semnopithecus priam) were also associated with outbreaks. These results suggest that increased monitoring of wildlife in areas of significant habitat fragmentation may add considerably to critical knowledge gaps in KFDV epidemiology and infection ecology and should be incorporated into novel One Health surveillance development for the region. In addition, the inclusion of some primate species as sentinels of KFDV circulation into general wildlife surveillance architecture may add further value.
Low mammalian species richness is associated with Kyasanur Forest disease outbreak risk in deforested landscapes in the Western Ghats, India. Michael G. Walsh, Rashmi Bhat, Venkatesh Nagarajan-Radha, Prakash Narayanan, Navya Vyas, Shailendra Sawleshwarkar, Chiranjay Mukhopadhyay. One Health, Volume 13, 2021, https://doi.org/10.1016/j.onehlt.2021.100299
Highly Pathogenic Avian Influenza (H5N1) Landscape Suitability Varies by Wetland Habitats and the Degree of Interface between Wild Waterfowl and Poultry in India
Highly pathogenic avian influenza (HPAI) virus, subtype H5N1, constitutes one of the world’s most important health and economic concerns given the catastrophic impact of epizootics on the poultry industry, the high mortality attending spillover in humans, and its potential as a source subtype for a future pandemic. Nevertheless, we still lack an adequate understanding of HPAI H5N1 epidemiology and infection ecology. The nature of the wild waterfowl–poultry interface, and the sharing of diverse wetland habitat among these birds, currently underscore important knowledge gaps. India has emerged as a global hotspot for HPAI H5N1, while also providing critical wintering habitat for many species of migratory waterfowl and year-round habitat for several resident waterfowl species. The current study sought to examine the extent to which the wild waterfowl–poultry interface, varied wetland habitat, and climate influence HPAI H5N1 epizootics in poultry in India. Using World Organisation for Animal Health reported outbreaks, this study showed that the wild waterfowl–poultry interface and lacustrine, riparian, and coastal marsh wetland systems were strongly associated with landscape suitability, and these relationships varied by scale. Although increasing poultry density was associated with increasing risk, this was only the case in the absence of wild waterfowl habitat, and only at a local scale. In landscapes increasingly shared between wild waterfowl and poultry, suitability was greater among lower density poultry, again at a local scale only. These findings provide further insight into the occurrence of HPAI H5N1 in India and suggest important landscape targets for blocking the waterfowl–poultry interface to interrupt virus transmission and prevent future outbreaks.
Walsh, M.G.; Mor, S.M.; Hossain, S. Highly Pathogenic Avian Influenza (H5N1) Landscape Suitability Varies by Wetland Habitats and the Degree of Interface between Wild Waterfowl and Poultry in India. Viruses 2020, 12, 1290. https://doi.org/10.3390/v12111290
Population structure and diet generalism define a preliminary ecological profile of zoonotic virus hosts in the Western Ghats, India
The rainforests of the Western Ghats exhibit some of the highest biodiversity on the planet, and yet are undergoing rapid land use change due to the expansion of agriculture and other industries. As the landscape of the region is transformed, more people are coming into conflict with wildlife and becoming exposed to pathogens that previously circulated beyond the boundaries of human incursion. Despite an ecological knowledge imperative, this emerging landscape is ill-defined with respect to the ecology of zoonotic viruses and their mammalian wildlife hosts. Without a better understanding of the underlying infection ecology, the epidemiology of viral spillover will remain elusive and unsuited to the task of predicting and preventing outbreaks. The current investigation explored the association between mammalian zoonotic virus richness and species-level landscape, life-history, and dietary traits to describe an initial ecological profile of zoonotic virus hosts in the Western Ghats. Social group composition and dietary forage were both non-linearly associated with greater zoonotic viral richness among these species, whereby species active in smaller social groups, albeit in higher population densities, and exhibiting a tendency toward a generalist diet hosted more zoonotic viruses. While these findings provide no definitive ecological demarcation of zoonotic virus hosts or their contribution to viral maintenance or amplification, it is expected that this preliminary profile can help to develop targeted wildlife pathogen surveillance programs and to expand the current approach to epidemiological modelling of emerging zoonoses in the region, which typically do not account for the macroecological parameters of infection transmission. https://doi.org/10.1016/j.epidem.2020.100416
Whence the next pandemic? The intersecting global geography of the animal-human interface, poor health systems and air transit centrality reveals conduits for high-impact spillover
The health and economic impacts of infectious disease pandemics are catastrophic as most recently manifested by coronavirus disease 2019 (COVID-19). The emerging infections that lead to substantive epidemics or pandemics are typically zoonoses that cross species boundaries at vulnerable points of animal-human interface. The sharing of space between wildlife and humans, and their domesticated animals, has dramatically increased in recent decades and is a key driver of pathogen spillover. Increasing animal-human interface has also occurred in concert with both increasing globalisation and failing health systems, resulting in a trifecta with dire implications for human and animal health. Nevertheless, to date we lack a geographical description of this trifecta that can be applied strategically to pandemic prevention. This investigation provides the first geographical quantification of the intersection of animal-human interfaces, poor human health system performance and global connectivity via the network of air travel. In so doing, this work provides a systematic, data-driven approach to classifying spillover hazard based on the distribution of animal-human interfaces while simultaneously identifying globally connected cities that are adjacent to these interfaces and which may facilitate global pathogen dissemination. We present this geography of high-impact spillover as a tool for developing targeted surveillance systems and improved health infrastructure in vulnerable areas that may present conduits for future pandemics. https://doi.org/10.1016/j.onehlt.2020.100177
A preliminary ecological profile of Kyasanur Forest disease virus hosts among the mammalian wildlife of the Western Ghats, India
Kyasanur Forest disease (KFD) is one of India’s severe arboviruses capable of causing prolonged debilitating disease. It has been expanding beyond its historical endemic locus at an alarming rate over the last two decades. The natural nidus of this zoonosis is located in the monsoon rainforest of the Western Ghats, India, which is one of the world’s most important biodiversity hotspots. Definitive reservoir hosts for KFD virus (KFDV) have yet to be delineated, and thus much of the infection ecology of this virus, and its consequent transmission dynamics, remains uncertain. Given its unique biogeographical context, identifying ecological parameters of KFDV relevant to the virus’ epidemiology has been complex and challenging. The challenge has been exacerbated by diminished research efforts in wildlife surveillance over the last two decades, coinciding with the expansion of the range of KFD across the region. The current investigation sought to define a preliminary ecological profile of KFDV hosts based on their life history and feeding traits to aid in re-establishing targeted wildlife surveillance and to discern those ecological traits of wildlife hosts that may improve our understanding of KFD epidemiology. The importance of fast-living among KFDV hosts was of special interest with respect to the latter aim. We compared mammalian traits between host and non-host species using general additive models and phylogenetic generalised linear models. This study found that both body mass and forest forage were strongly associated with mammalian host infection status, but that reproductive life history traits were not. These findings will help in structuring ecologically based wildlife surveillance and field investigations, while also helping to parameterise novel epidemiological models of zoonotic infection risk that incorporate species functional traits in a region where biogeography, landscape ecology, and community ecology manifest extraordinary complexity, particularly under growing anthropogenic pressure. https://www.sciencedirect.com/science/article/abs/pii/S1877959X19304169?via%3Dihub#upi0005 https://doi.org/10.1016/j.ttbdis.2020.101419
Forest loss shapes the landscape suitability of Kyasanur Forest disease in the biodiversity hotspots of the Western Ghats, India
Anthropogenic pressure in biodiversity hotspots is increasingly recognized as a major driver of the spillover and expansion of zoonotic disease. In the Western Ghats region of India, a devastating tick-borne zoonosis, Kyasanur Forest disease (KFD), has been expanding rapidly beyond its endemic range in recent decades. It has been suggested that anthropogenic pressure in the form of land use changes that lead to the loss of native forest may be directly contributing to the expanding range of KFD, but clear evidence has not yet established the association between forest loss and KFD risk. The current study sought to investigate the relationship between KFD landscape suitability and both forest loss and mammalian species richness, to inform its epidemiology and infection ecology. A total of 47 outbreaks of KFD between 1 January 2012 and 30 June 2019 were modelled as an inhomogeneous Poisson process. Both forest loss [relative risk (RR) = 1.83; 95% confidence interval (CI) 1.33–2.51] and mammalian species richness (RR = 1.29; 95% CI 1.16–1.42) were strongly associated with increased risk of KFD and dominated its landscape suitability. These results provide the first evidence of a clear association between increasing forest loss and risk for KFD. Moreover, the findings also highlight the importance of forest loss in areas of high biodiversity. Therefore, this evidence provides strong support for integrative approaches to public health which incorporate conservation strategies simultaneously protective of humans, animals and the environment.
Michael G Walsh, Siobhan M Mor, Hindol Maity, Shah Hossain, Forest loss shapes the landscape suitability of Kyasanur Forest disease in the biodiversity hotspots of the Western Ghats, India, International Journal of Epidemiology, , dyz232, https://doi.org/10.1093/ije/dyz232
The elephant–livestock interface modulates anthrax suitability in India
Anthrax is a potentially life-threatening bacterial disease that can spread between wild and livestock animals and humans. Transmission typically occurs indirectly via environmental exposure, with devastating consequences for human and animal health, as well as pastoralist economies. India has a high annual occurrence of anthrax in some regions, but a country-wide delineation of risk has not yet been undertaken. The current study modelled the geographical suitability of anthrax across India and its associated environmental features using a biogeographic application of machine learning. Both biotic and abiotic features contributed to risk across multiple scales of influence. The elephant–livestock interface was the dominant feature in delineating anthrax suitability. In addition, water–soil balance, soil chemistry and historical forest loss were also influential. These findings suggest that the elephant–livestock interface plays an important role in the cycling of anthrax in India. Livestock prevention efforts targeting this interface, particularly within anthropogenic ecotones, may yield successes in reducing ongoing transmission between animal hosts and subsequent zoonotic transmission to humans.
Michael G. Walsh, Siobhan M. Mor, Shah Hossain. The elephant–livestock interface modulates anthrax suitability in India. 286. Proceedings of the Royal Society B: Biological Sciences http://doi.org/10.1098/rspb.2019.0179
Ecological and life history traits are associated with Ross River virus infection among sylvatic mammals in Australia
Background: Ross River virus (RRV) is Australia’s most important arbovirus given its annual burden of disease and the relatively large number of Australians at risk for infection. This mosquito-borne arbovirus is also a zoonosis, making its epidemiology and infection ecology complex and cryptic. Our grasp of enzootic, epizootic, and zoonotic RRV transmission dynamics is imprecise largely due to a poor understanding of the role of wild mammalian hosts in the RRV system.
Methods: The current study applied a piecewise structural equation model (PSEM) toward an interspecific comparison of sylvatic Australian mammals to characterize the ecological and life history profile of species with a history of RRV infection relative to those species with no such history among all wild mammalian species surveyed for RRV infection. The effects of species traits were assessed through multiple causal pathways within the PSEM framework.
Results: Sylvatic mammalian species with a history of RRV infection tended to express dietary specialization and smaller population density. These species were also characterized by a longer gestation length.
Conclusions: This study provides the first interspecific comparison of wild mammals for RRV infection and identifies some potential targets for future wildlife surveys into the infection ecology of this important arbovirus. An applied RRV macroecology may prove invaluable to the epidemiological modeling of RRV epidemics across diverse sylvatic landscapes, as well as to the development of human and animal health surveillance systems.
Michael G. Walsh BMC Ecology201919:2 https://doi.org/10.1186/s12898-019-0220-5.
Climatic influence on anthrax suitability in warming northern latitudes
Climate change is impacting ecosystem structure and function, with potentially drastic downstream effects on human and animal health. Emerging zoonotic diseases are expected to be particularly vulnerable to climate and biodiversity disturbance. Anthrax is an archetypal zoonosis that manifests its most significant burden on vulnerable pastoralist communities. The current study sought to investigate the influence of temperature increases on geographic anthrax suitability in the temperate, boreal, and arctic North, where observed climate impact has been rapid. This study also explored the influence of climate relative to more traditional factors, such as livestock distribution, ungulate biodiversity, and soil-water balance, in demarcating risk. Machine learning was used to model anthrax suitability in northern latitudes. The model identified climate, livestock density and wild ungulate species richness as the most influential features in predicting suitability. These findings highlight the significance of warming temperatures for anthrax ecology in northern latitudes, and suggest potential mitigating effects of interventions targeting megafauna biodiversity conservation in grassland ecosystems, and animal health promotion among small to midsize livestock herds. Michael G. Walsh, Allard W. de Smalen & Siobhan M. Mor. Scientific Reports volume 8, Article number: 9269 (2018). https://rdcu.be/Z8Vg
Interspecific network centrality, host range and early‐life development are associated with wildlife hosts of Rift Valley fever virus
Rift Valley fever virus (RVFV) is responsible for a substantive disease burden in pastoralist communities and the agricultural sector in the African continent and Arabian Peninsula. Enzootic, epizootic and zoonotic RVFV transmission dynamics remain ill‐defined, particularly due to a poor understanding of the role of mammalian hosts in the epidemiology and infection ecology of this arbovirus. Using a piecewise structural equation model, this study sought to identify associations between biological and ecological characteristics of mammalian species and documented RVFV infection to highlight species‐level traits that may influence wildlife host status. Interspecific network centrality, size of species home range and reproductive life‐history traits were all associated with being an RVFV host. The identification of these species‐level characteristics may help to provide ecological context for the role of wildlife amplification hosts in the epidemiology of spillover to livestock and humans and may also help to identify specific points of vulnerability at the wildlife–livestock interface. Walsh and Mor. Transboundary and Emerging Diseases. 2018 May 13. doi: 10.1111/tbed.12903
Hydrological features and the ecological niches of mammalian hosts delineate elevated risk for Ross River virus epidemics in anthropogenic landscapes in Australia
The current understanding of the landscape epidemiology of Ross River virus (RRV), Australia’s most common arthropod-borne pathogen, is fragmented due to gaps in surveillance programs and the relatively narrow focus of the research conducted to date. This leaves public health agencies with an incomplete understanding of the spectrum of infection risk across the diverse geography of the Australian continent. The current investigation sought to assess the risk of RRV epidemics based on abiotic and biotic landscape features in anthropogenic landscapes, with a particular focus on the influence of water and wildlife hosts.
Abiotic features, including hydrology, land cover and altitude, and biotic features, including the distribution of wild mammalian hosts, were interrogated using a Maxent model to discern the landscape suitability to RRV epidemics in anthropogenically impacted environments across Australia.
Water-soil balance, proximity to controlled water reservoirs, and the ecological niches of four species (Perameles nasuta, Wallabia bicolor, Pseudomys novaehollandiae and Trichosurus vulpecula) were important features identifying high risk landscapes suitable for the occurrence of RRV epidemics.
These results help to delineate human infection risk and thus provide an important perspective for geographically targeted vector, wildlife, and syndromic surveillance within and across the boundaries of local health authorities. Importantly, our analysis highlights the importance of the hydrology, and the potential role of mammalian host species in shaping RRV epidemic risk in peri-urban space. This study offers novel insight into wildlife hosts and RRV infection ecology and identifies those species that may be beneficial to future targeted field surveillance particularly in ecosystems undergoing rapid change. Walsh and Webb Parasites & Vectors (2018) 11:192. https://doi.org/10.1186/s13071-018-2776-x
The impact of human population pressure on flying fox niches and the potential consequences for Hendra virus spillover
Hendra virus (HeV) is an emerging pathogen of concern in Australia given its ability to spillover from its reservoir host, pteropid bats, to horses and further on to humans, and the severe clinical presentation typical in these latter incidental hosts. Specific human pressures over recent decades, such as expanding human populations, urbanization, and forest fragmentation, may have altered the ecological niche of Pteropus species acting as natural HeV reservoirs and may modulate spillover risk. This study explored the influence of inter-decadal net human local migration between 1970 and 2000 on changes in the habitat suitability to P. alecto and P. conspicillatus from 1980 to 2015 in eastern Australia. These ecological niches were modeled using boosted regression trees and subsequently fitted, along with additional landscape factors, to HeV spillovers to explore the spatial dependency of this zoonosis. The spatial model showed that the ecological niche of these two flying fox species, the human footprint, and proximity to woody savanna were each strongly associated with HeV spillover and together explained most of the spatial dependency exhibited by this zoonosis. These findings reinforce the potential for anthropogenic pressures to shape the landscape epidemiology of HeV spillover. Scientific Reports 7, Article number: 8226 (2017) doi:10.1038/s41598-017-08065-z
Wetlands, wild Bovidae species richness and sheep density delineate risk of Rift Valley fever outbreaks in the African continent and Arabian Peninsula
Rift Valley fever (RVF) is an emerging, vector-borne viral zoonosis that has significantly impacted public health, livestock health and production, and food security over the last three decades across large regions of the African continent and the Arabian Peninsula. The potential for expansion of RVF outbreaks within and beyond the range of previous occurrence is unknown. Despite many large national and international epidemics, the landscape epidemiology of RVF remains obscure, particularly with respect to the ecological roles of wildlife reservoirs and surface water features. The current investigation modeled RVF risk throughout Africa and the Arabian Peninsula as a function of a suite of biotic and abiotic landscape features using machine learning methods. Intermittent wetland, wild Bovidae species richness and sheep density were associated with increased landscape suitability to RVF outbreaks. These results suggest the role of wildlife hosts and distinct hydrogeographic landscapes in RVF virus circulation and subsequent outbreaks may be underestimated. These results await validation by studies employing a deeper, field-based interrogation of potential wildlife hosts within high risk taxa.
Walsh MG, Willem de Smalen A, Mor SM (2017) Wetlands, wild Bovidae species richness and sheep density delineate risk of Rift Valley fever outbreaks in the African continent and Arabian Peninsula. PLoS Negl Trop Dis 11(7): e0005756. https://doi.org/10.1371/journal.pntd.0005756
Global Seasonal Clustering of H5N1 Avian Influenza
Highly pathogenic avian influenza subtype H5N1 (H5N1) has contributed to substantial economic loss for backyard and large scale poultry farmers each year since 1997. While the distribution of domestic H5N1 outbreaks across Africa, Europe and Asia is extensive, those features of the landscape conferring greatest risk remain uncertain. Furthermore, the extent to which influential landscape features may vary by season has been inadequately described. The current investigation used World Organization for Animal Health surveillance data to 1) delineate areas at greatest risk for H5N1 epizootics among domestic poultry, 2) identify those abiotic and biotic features of the landscape associated with outbreak risk, and 3) examine patterns of epizootic clustering by season. Inhomogeneous point process models were used to predict the intensity of H5N1 outbreaks and describe the spatial dependencies between them. During October through March, decreasing precipitation, increasing isothermality, and the presence of H5N1 in wild birds were significantly associated with increased risk of domestic H5N1 epizootics. Conversely, increasing precipitation and decreasing isothermality were associated with increased risk during April through September. Increasing temperature during the coldest quarter, domestic poultry density, and proximity to surface water were associated with increased risk of domestic outbreaks throughout the year. Spatial dependencies between outbreaks appeared to vary seasonally, with substantial clustering at small and large scale identified during October through March even after accounting for inhomogeneity due to landscape factors. In contrast, during April to September, H5N1 outbreaks exhibited no clustering at small scale once accounting for landscape factors. This investigation has identified seasonal differences in risk and clustering patterns of H5N1 outbreaks in domestic poultry, and may suggest strategies in high risk areas with features amenable to intervention such as controlling domestic bird movement in areas of high poultry density or preventing contact between poultry and wild birds and/or surface water features.
Walsh, MG, Amstislavski P, Andrea Greene, Haseeb, MA. The landscape epidemiology of seasonal clustering of highly pathogenic avian influenza (H5N1) in domestic poultry in Africa, Europe and Asia. Transboundary and Emerging Diseases 2016 Jun 16. doi: 10.1111/tbed.12537. Epub ahead of print.
The Ecologic Niche of Plague in the Western US
Plague has been established in the western United States (US) since 1900 following the west coast introduction of commensal rodents infected with Yersinia pestis via early industrial shipping. Over the last century, plague ecology has transitioned through cycles of widespread human transmission, urban domestic transmission among commensal rodents, and ultimately settled into the predominantly sylvan foci that remain today where it is maintained alternatively by enzootic and epizootic transmission. While zoonotic transmission to humans is much less common in modern times, significant plague risk remains in parts of the western US. Moreover, risk to some threatened species that are part of the epizootic cycle can be quite substantive. This investigation attempted to predict the risk of plague across the western US by modeling the ecologic niche of plague in sylvan and domestic animals identified between 2000 and 2015. A Maxent machine learning algorithm was used to predict this niche based on climate, altitude, land cover, and the presence of an important enzootic species, Peromyscus maniculatus. This model demonstrated good predictive ability (AUC = 86%) and identified areas of high risk in central Colorado, north-central New Mexico, and southwestern and northeastern California. The presence of P. maniculatus, altitude, precipitation during the driest and wettest quarters, and distance to artificial surfaces, all contributed substantively to maximizing the gain function. These findings add to the known landscape epidemiology and infection ecology of plague in the western US and may suggest locations of particular risk to be targeted for wild and domestic animal intervention.
Walsh, MG and Haseeb, MA. Modeling the ecologic niche of plague in sylvan and domestic animal hosts to delineate sources of human exposure in the western United States. PeerJ. 2015 Dec 14;3:e1493. doi: 10.7717/peerj.1493.
Nipah Virus Spillover
Nipah virus (NiV) is a significant emerging zoonotic pathogen given its wide geographic distribution, and the severe morbidity and high mortality that accompanies infection. Moreover, the layered landscape epidemiology surrounding spillover from reservoir host species to humans is ill-defined. Identifying landscape features that contribute to NiV spillover would likely prove helpful in preventing emergence in human populations. Using an inhomogeneous Poisson model, this study investigated the role of vegetation cover, the human footprint (HFP), and reservoir Pteropus bat distribution to identify the spatial dependence of spillover and map risk across South and Southeast Asia. The spatial model identified HFP (RR = 1.08, 95% C.I. 1.05 – 1.11) and bat distribution (RR = 19.44, 95% C.I 1.92 – 196.7) as significant predictors of NiV risk, while vegetation cover was not significant after accounting for HFP and the presence of Pteropus bats. These findings further inform the landscape epidemiology of NiV and suggest specific conduits for spillover in the landscape. However, more detailed field studies will be required to validate these results.
Walsh, MG. Mapping the risk of Nipah virus spillover into human populations in South and Southeast Asia. Trans R Soc Trop Med Hyg. 2015 Sep;109(9):563-71. doi: 10.1093/trstmh/trv055.
Ebola Virus Disease
Ebola virus disease (EVD) is an emerging infectious disease of zoonotic origin that has been responsible for high mortality and significant social disruption in West and Central Africa. Zoonotic transmission of EVD requires contact between susceptible human hosts and the reservoir species for Ebolaviruses, which are believed to be fruit bats. Nevertheless, features of the landscape that may facilitate such points of contact have not yet been adequately identified. Nor have spatial dependencies between zoonotic EVD transmission and landscape structures been delineated. This investigation sought to describe the spatial relationship between zoonotic EVD transmission events, or spillovers, and population density and vegetation cover. An inhomogeneous Poisson process model was fitted to all precisely geolocated zoonotic transmissions of EVD in West and Central Africa. Population density was strongly associated with spillover; however, there was significant interaction between population density and green vegetation cover. In areas of very low population density, increasing vegetation cover was associated with a decrease in risk of zoonotic transmission, but as population density increased in a given area, increasing vegetation cover was associated with increased risk of zoonotic transmission. This study showed that the spatial dependencies of Ebolavirus spillover were associated with the distribution of population density and vegetation cover in the landscape, even after controlling for climate and altitude. While this is an observational study, and thus precludes direct causal inference, the findings do highlight areas that may be at risk for zoonotic EVD transmission based on the spatial configuration of important features of the landscape.
Walsh MG, Haseeb M. (2015) The landscape configuration of zoonotic transmission of Ebola virus disease in West and Central Africa: interaction between population density and vegetation cover. PeerJ 3:e735https://dx.doi.org/10.7717/peerj.735
Rats in New York City
Rats are ubiquitous in urban environments and, as established reservoirs for infectious pathogens, present a control priority for public health agencies. New York City (NYC) harbors one of the largest rat populations in the United States, but surprising little study has been undertaken to define rat ecology across varied features of this urban landscape. More importantly, factors that may contribute to increased encounters between rats and humans have rarely been explored. Using city-wide records of rat sightings reported to the NYC Department of Health and Mental Hygiene, this investigation sought to identify sociodemographic, housing, and physical landscape characteristics that are associated with increased rat sightings across NYC census tracts. A hierarchical Bayesian conditional autoregressive Poisson model was used to assess these associations while accounting for spatial heterogeneity in the variance. Closer proximity to both subway lines and recreational public spaces was associated with a higher concentration of rat sightings, as was a greater presence of older housing, vacant housing units, and low education among the population. Moreover, these aspects of the physical and social landscape accurately predicted rat sightings across the city. These findings have identified specific features of the NYC urban environment that may help to provide direct control targets for reducing human–rat encounters.
Walsh MG. (2014) Rat sightings in New York City are associated with neighborhood sociodemographics, housing characteristics, and proximity to open public space. PeerJ 2:e533 https://dx.doi.org/10.7717/peerj.533
Predicting toxocariasis in New York City
Toxocariasis is increasingly recognized as an important neglected infection of poverty (NIP) in developed countries, and may constitute the most important NIP in the United States (US) given its association with chronic sequelae such as asthma and poor cognitive development. Its potential public health burden notwithstanding, toxocariasis surveillance is minimal throughout the US and so the true burden of disease remains uncertain in many areas. The Third National Health and Nutrition Examination Survey conducted a representative serologic survey of toxocariasis to estimate the prevalence of infection in diverse US subpopulations across different regions of the country. Using the NHANES III surveillance data, the current study applied the predicted probabilities of toxocariasis to the sociodemographic composition of New York census tracts to estimate the local probability of infection across the city. The predicted probability of toxocariasis ranged from 6% among US-born Latino women with a university education to 57% among immigrant men with less than a high school education. The predicted probability of toxocariasis exhibited marked spatial variation across the city, with particularly high infection probabilities in large sections of Queens, and smaller, more concentrated areas of Brooklyn and northern Manhattan. This investigation is the first attempt at small-area estimation of the probability surface of toxocariasis in a major US city. While this study does not define toxocariasis risk directly, it does provide a much needed tool to aid the development of toxocariasis surveillance in New York City.
Walsh MG, Haseeb MA (2014) Small-Area Estimation of the Probability of Toxocariasis in New York City Based on Sociodemographic Neighborhood Composition. PLoS ONE 9(6): e99303. doi:10.1371/journal.pone.0099303
Forest Fragmentation and Babesiosis in New York State
Babesiosis is an emerging arthropod-borne infection that has been increasing in incidence for the last decade in the northeastern United States. Babesiosis may share features of its landscape epidemiology with other arthropod-borne infections transmitted by the same tick vectors in similar geographic spaces. This study examined 11 years of surveillance data in New York State to measure the relationship between forest fragmentation and the incidence of human babesiosis. Adjusted Poisson models showed that increasing edges of contact between forested land and developed land, as measured by their shared perimeters, was associated with a higher incidence of babesiosis cases (incident rate ratio [IRR]=1.015, 95% confidence interval [CI] 1.01-1.02; p<0.001), even after controlling for the total developed land area and forest density, and temperature and precipitation. Each 10-km increase in perimeter contact between forested land and developed land per county was associated with a 1.5% increase in babesiosis risk. Higher temperature was also strongly associated with increasing babesiosis risk (IRR=1.18, 95% CI 1.10-1.27; p<0.001), wherein each degree Celsius increase was associated with an 18% increase in babesiosis risk. While direct causal conclusions cannot be drawn from these data, these findings do identify a potentially important signal in the epidemiology of babesiosis and suggest that the underlying physical landscape may play a role in shaping points of contact between humans and tick vectors and the subsequent transmission of Babesia microti.
Walsh MG. The relevance of forest fragmentation on the incidence of human babesiosis: investigating the landscape epidemiology of an emerging tick-borne disease. Vector Borne Zoonotic Dis. 2013 Apr;13(4):250-5. doi: 10.1089/vbz.2012.1198.
Hydrogeography and Climate in the Landscape Epidemiology of West Nile Virus in New York State
The epidemiology and ecology of West Nile virus (WNV) have not yet been completely described. In particular, the specific roles of climate and water in the landscape in the occurrence of human WNV cases remain unknown. This study used Poisson regression to describe the relationships between WNV cases and temperature, precipitation, and the hydrogeography of the landscape in New York State from 2000 to 2010. Fully adjusted models showed that hydrogeographic area was significantly inversely associated with WNV cases (incidence rate ratio (IRR) = 0.99; 95% C.I. = 0.98–0.997, p = 0.04), such that each one square kilometer increase in hydrogeographic area was associated with a 1% decrease in WNV incidence. This association was independent of both temperature, which was also associated with WNV incidence (IRR = 2.06; 95% C.I. = 1.84–2.31, p<0.001), and precipitation, which was not (IRR = 1.0; 95% C.I. = 0.99–1.01, p = 0.16). While the results are only suggestive due to the county-level aggregated data, these findings do identify a potentially important surveillance signal in the landscape epidemiology of WNV infection.
Walsh MG (2012) The Role of Hydrogeography and Climate in the Landscape Epidemiology of West Nile Virus in New York State from 2000 to 2010. PLoS ONE 7(2): e30620. doi:10.1371/journal.pone.0030620