A social-ecological systems perspective of huanglongbing management in California

Huanglongbing (HLB) is an invasive disease of citrus trees associated with the bacterium “Candidatus Liberibacter asiaticus” and transmitted by the Asian citrus psyllid (ACP), Diaphorina citri, that is threatening citrus production in California and other citrus-producing areas of the world. Current strategies to prevent citrus trees from being infected with HLB are based on the application of coordinated insecticide treatments for the insect vector, detection and removal of HLB-positive trees and use of certified plant material. These measures are most effective if applied on an area-wide scale by all citrus growers in a region, yet little is known about the California citrus growers’ willingness to coordinate measures across property boundaries. When individuals need to make contributions to achieve a collective effort but may benefit from the efforts of others without bearing the costs, they may be tempted to free-ride on others’ efforts, giving rise to a collective action problem. This type of problem has been extensively studied by the social-ecological systems literature, but it has rarely been addressed in the context of plant diseases. In this dissertation, a social-ecological systems perspective was used to integrate the social and ecological dimensions of HLB management in order to explore what strategies may be more effective to achieve collective action for this disease. The first chapter introduces the idea of plant health provision as a public good collective action problem. Ostrom’s design principles for long-enduring common-pool resource institutions are used as a reference to compare the institutional approaches that have been developed to achieve collective action for HLB in California and other citrus-producing areas, illustrating how these principles could be applied to other plant diseases that are threatening food security, and suggesting a link between institutional approaches that follow the design principles and successful collective outcomes. The second chapter explores the California citrus industry’s propensity to adopt voluntary measures to manage HLB. A multivariate ordinal logistic regression model is used to analyze a survey distributed to 300 participants, showing that the propensity to adopt management measures may depend on the citrus stakeholder’s perceived vulnerability to HLB, as well as their intention to stay informed and communicate with the regional coordinators of the HLB control program and their neighbors. In addition, the analysis sheds light into what combinations of management measures may be adopted together as an integrated pest management approach to HLB. The third chapter focuses on the area-wide management (AWM) program for ACP in Southern California, examining the individual perceptions and group-level determinants of collective action for AWM. It shows that citrus stakeholders are aware of the benefits of coordinating insecticide treatments for ACP, but they identify the lack of participation as the main obstacle for collective action, and some do not believe that their neighbors will coordinate. To face this collective action problem, two distinct institutional approaches have been developed to coordinate insecticide treatments for ACP, one in which treatments are voluntary, and one in which they are mandatory. An analysis of participation in AWM in Southern California over nine seasons shows that these two institutional approaches have followed a different trajectory over time. In addition, group-level variables from collective action theory, such as the size of the group or the heterogeneity in grove size, have had a negative impact on participation and may be relevant for the design of future AWM programs. This dissertation contributes to answering the question of what institutional approaches and strategies might be more effective to deal with the spatial and temporal dynamics of plant diseases while staying aligned with the preferences, values and needs of the societies affected, setting the basis for further interdisciplinary research that will likely benefit the management of HLB and other plant diseases that give rise to collective action problems

Using models to provide rapid programme support for California's efforts to suppress Huanglongbing disease of citrus

We describe a series of operational questions posed during the state-wide response in California to the arrival of the invasive citrus disease Huanglongbing. The response is coordinated by an elected committee from the citrus industry and operates in collaboration with the California Department of Food and Agriculture, which gives it regulatory authority to enforce the removal of infected trees. The paper reviews how surveillance for disease and resource allocation between detection and delimitation have been addressed, based on epidemiological principles. In addition, we describe how epidemiological analyses have been used to support rule-making to enact costly but beneficial regulations and we highlight two recurring themes in the programme support work: (i) data are often insufficient for quantitative analyses of questions and (ii) modellers and decision-makers alike may be forced to accept the need to make decisions on the basis of simple or incomplete analyses that are subject to considerable uncertainty. This article is part of the theme issue 'Modelling infectious disease outbreaks in humans, animals and plants: epidemic forecasting and control'. This theme issue is linked with the earlier issue 'Modelling infectious disease outbreaks in humans, animals and plants: approaches and important themes'

The ABO blood group locus and a chromosome 3 gene cluster associate with SARS-CoV-2 respiratory failure in an Italian-Spanish genome-wide association analysis

[Background] Respiratory failure is a key feature of severe Covid-19 and a critical driver of mortality, but for reasons poorly defined affects less than 10% of SARS-CoV-2 infected patients.[Methods] We included 1,980 patients with Covid-19 respiratory failure at seven centers in the Italian and Spanish epicenters of the SARS-CoV-2 pandemic in Europe (Milan, Monza, Madrid, San Sebastian and Barcelona) for a genome-wide association analysis. After quality control and exclusion of population outliers, 835 patients and 1,255 population-derived controls from Italy, and 775 patients and 950 controls from Spain were included in the final analysis. In total we analyzed 8,582,968 single-nucleotide polymorphisms (SNPs) and conducted a metaanalysis of both case-control panels.[Results] We detected cross-replicating associations with rs11385942 at chromosome 3p21.31 and rs657152 at 9q34, which were genome-wide significant (P<5×10-8) in the meta-analysis of both study panels, odds ratio [OR], 1.77; 95% confidence interval [CI], 1.48 to 2.11; P=1.14×10-10 and OR 1.32 (95% CI, 1.20 to 1.47; P=4.95×10-8), respectively. Among six genes at 3p21.31, SLC6A20 encodes a known interaction partner with angiotensin converting enzyme 2 (ACE2). The association signal at 9q34 was located at the ABO blood group locus and a blood-group-specific analysis showed higher risk for A-positive individuals (OR=1.45, 95% CI, 1.20 to 1.75, P=1.48×10-4) and a protective effect for blood group O (OR=0.65, 95% CI, 0.53 to 0.79, P=1.06×10-5).[Conclusions] We herein report the first robust genetic susceptibility loci for the development of respiratory failure in Covid-19. Identified variants may help guide targeted exploration of severe Covid19 pathophysiology.The IKMB's core facilities received infrastructure support by the Deutsche Forschungsgemeinschaft (DFG) Cluster of Excellence "Precision Medicine in Chronic Inflammation" (PMI, EXC2167). The project also received support through a philanthropic donation by Stein Erik Hagen and Canica AS. L.V. was funded by the Fondazione IRCCS Ca’ Granda «COVID-19 Biobank» research grant. This work was also supported by the Ministero dell’Istruzione, dell’Università e della Ricerca – MIUR project "Dipartimenti di Eccellenza 2018 – 2022" (n° D15D18000410001) to the Department of Medical Sciences, University of Torino. The IKMB authors received financial support from the UKSH Foundation "Gutes Tun!" (special thanks to Alexander Eck, Jenspeter Horst and Jens Scholz) and the German Federal Ministry of Education and Research (BMBF; grant ID 01KI20197). HLA-Typing was performed and supported by the Stefan-MorschStiftung. M.A.H was supported by the Spanish Ministry of Science and Innovation ‘JdC fellowship IJC2018-035131-I.N