Previous analyses using logistic regression models with the same dataset revealed the combination of risk factors that were supported by our data [62] . Five factors were initially investigated: age (AGE), sex (SEX), way of life (owned or unowned, WOL), orange phenotype (orange or non orange, PHENO) and body mass (MASS) and one correction factor (the population of origin, POP) was considered. For each virus, the most appropriate model was selected using the Akaike Information Criterion adjusted for small sample size (AICc, [81] ). Ideally, all factors potentially creating apparent associations should be included in the model. But to limit the number of correction risk factors, the minimal model containing the identified risk factors for the two viruses was retained as a compromise for each pair (Table 1) .