Abstract
AbstractXylella fastidiosa is an important insect‐vectored bacterial plant pathogen with a wide host range, causing significant economic impact in the agricultural and horticultural industries. Once restricted to the Americas, severe European outbreaks have been discovered recently in Italy, Spain, France, and Portugal. The Italian outbreak, detected in Puglia in 2013, has spread over 100 km, killing millions of olive trees, and is still expanding. To date, quantified assessment of important epidemiological parameters useful for risk assessment and management, such as transmission rates, symptomless periods, and time to death in field populations, has been lacking. This is due to the emergent and novel nature of the outbreak and length of time needed to monitor the course of disease progression. To address this, we developed a Bayesian method to infer epidemiological parameters by fitting and comparing compartmental epidemiological models to short snapshots of disease progression observed in multiple field plots. We estimated that each infected tree with symptoms is able to infect around 19 trees per year (95% credible range 14–26). The symptomless stage was estimated to have low to negligible infectivity and to last an average of approximately 1.2 years (95% credible range 1.0–1.3 years). Tree desiccation was estimated to occur approximately 4.3 years (95% credible range 4.0–4.6 years) after symptom appearance. However, we were unable to estimate the infectiousness of desiccated trees from the data. Our method could be used to make early estimates of epidemiological parameters in other emerging disease outbreaks where symptom expression is slow.
Highlights
Emerging infectious diseases and invasive species are of significant global concern for economies and public health, and are on the rise due to socioeconomic, ecological, and environmental factors, such as human population density and growth, drug resistance, and host richness (Jones et al, 2008)
We reveal the sensitivity of the models to each of these parameters and how they contribute to the overall epidemic
Accounting for the 3-year delay before desiccation, the estimated mean time from symptom establishment to desiccation (τ+TD) was 4.3 years (95% credible range 4.0–4.6 years; TA B L E 1 Comparison between the generalized full epidemiological model (SIAISID) of Xylella fastidiosa infecting olive trees and simpler specifications, in which relative infectivity of symptomless or desiccated trees are fixed rather than estimated
Summary
Emerging infectious diseases and invasive species are of significant global concern for economies and public health, and are on the rise due to socioeconomic, ecological, and environmental factors, such as human population density and growth, drug resistance, and host richness (Jones et al, 2008). Other strains and outbreaks of the bacterium have since been discovered in other host plants in Spain, France, other regions of Italy (Tuscany), and Portugal (EFSA Panel on Plant Health, 2019a). The symptomless period under field conditions has yet to be formally quantified This is an important parameter to estimate because the visualization of symptoms is key for policy implications in transporting olive trees, and containment and control measures (e.g., Decision [EU] 2015/789 and Decision [EU] 2017/2352); these measures include establishing a demarcated area around detected infected areas with specific requirements associated with plant movement into or within the EU, surveillance, plant removal, and other management measures including agricultural practices to control vector populations. We reveal the sensitivity of the models to each of these parameters and how they contribute to the overall epidemic
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