Submitted to: International Organization of Citrus Virologists Proceedings
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2005
Publication Date: 3/18/2005
Citation: Gottwald, T.R., Taylor, E.L. 2005. Using survival analysis to predict the risk of infection in a ctv epidemic. International Organization of Citrus Virologists Proceedings.
Technical Abstract: The spatial and temporal aspects of Citrus Tristeza Virus (CTV) during epidemics have been described previously for both the CTV/Toxoptera citricida and CTV/Aphis gossypii pathosystems. For CTV/T. citricida pathosystem, aggregation of infected trees occurs presumably due to movement of viruliferous aphids within local areas of influence. In addition, long distance spread of CTV has been document for both pathosystems. One question that arises is, What threat does individual CTV-infected trees present to neighboring trees? Survival analysis was used to examine the probability of survival (remaining in a non-infected state) of CTV-free trees when located at various distances of proximity to CTV-infected trees through time. A risk index was calculated via a modified Cox proportional hazards model to estimate the probability of survival through time of CTV-free trees when located at various distances to trees that became CTV-infected in prior years. The risk of becoming infected was related to previous reported 'local areas of influence'. It was found that a substantial proportion of newly infected trees within a planting could be accounted by trees determined to be infected 6 months previous within a 'local area of influence' of approximately 24m radius and that 'survival' decreased significantly through time.