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

Abstract

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’.

Citrus vascular proteomics highlights the role of peroxidases and serine proteases during Huanglongbing disease progression

“…In the United States, HLB was first diagnosed in 2005 in Florida and has since spread to Texas, Louisiana, South Carolina, Georgia and California (4). In California, CLas positive citrus was detected in 2012 and there are currently 1,788 positive plants identified by qPCR (5,6). In Florida, it is estimated that 95% of mature trees in commercial groves are infected, resulting in a loss of over 7.8 billion dollars in revenue and 7,500 jobs since 2007 (7).…”

Status of Huanglongbing (HLB) outbreaks in Florida, California and Texas

“…The CPDPC is a grower-funded organization that makes recommendations to, and is under the jurisdiction of CDFA. The CPDPC's recommendations provide a coordinated response to suppress ACP populations and mitigate the spread of HLB (McRoberts et al 2019). Additionally, the California Secretary of Agriculture executed a state mandate requiring removal of any tree confirmed as CLas-positive.…”

“…To effectively address HLB mitigation, CDFA needed to employ wide-scale surveillance to find the pathogen and vector as early as possible. Therefore, rather than simply deploying a stratified type survey over the region, they turned instead to a more proactive surveillance approach that targets the probability of an area becoming infected, based on a number of previously identified epidemiological risk factors (Gottwald et al 2013(Gottwald et al , 2018(Gottwald et al , 2019McRoberts et al 2019). These risk factors were extensively explored during HLB epidemics in China, Brazil, and Florida (Gottwald 2010).…”

“…In addition, it was demonstrated that the RBS accounted for increased risk surrounding these quarantine areas, resulting in a corresponding intensification of surveillance in the proximal areas. Based on these analytical findings and intensified RBS in the adjacent areas, the CPDPC recommended to CDFA and USDA/APHIS that the quarantine treatment areas could be reduced to 400 m. This reduction was accepted and enacted in early 2019 (McRoberts et al 2019).…”

Detection, forecasting and control of infectious disease epidemics: modelling outbreaks in humans, animals and plants

“…Accordingly, epidemiological models of pathogens of humans, animals and plants often include a spatial component. In this issue, there are examples of spatial livestock disease models based on cattle movements [50], a spatial model of wildlife rabies [78] and spatial models of huanglongbing disease of citrus plants [16,62] (e.g. figure 3c).…”