The Italian Xylella fastidiosa outbreak, detected in Apulia in 2013, has spread over 100 km, killing millions of olive trees and is still expanding.
Given the slow emergence of symptoms, the novel nature of the outbreak, and the time required to monitor the disease progression, a quantified assessment of important epidemiological parameters has been lacking.
The researchers developed a Bayesian method to infer those parameters – transmission rates, symptomless periods, and time to death in field populations – by fitting and comparing epidemiological models to snapshots of disease progression observed in multiple olive field plots in Apulia.
Researchers estimated that each infected tree with symptoms could infect around 19 trees per year (95% credible range 14–26). The symptomless stage, estimated to have low to little infectivity, lasts an average of approximately 1.2 years (95% credible range 1.0–1.3 years). Tree desiccation can occur about 4.3 years (95% credible range 4.0–4.6 years) after symptom appearance.
The research suggests that due to the relatively low infectiousness of asymptomatic trees compared to symptomatic trees, early detection and removal of asymptomatic trees would aid in halting disease spread in the region.
Estimating the epidemiology of emerging Xylella fastidiosa outbreaks in olives
https://doi.org/10.1111/ppa.13238 | via Plant Pathology