This passage discusses viruses that are maintained over extended periods, sometimes even throughout the entire lifespan, through transmission from infected to healthy plants by vectors. These viruses exhibit distinct transmission traits, such as passing through the moult, and some can pass on to the vector’s offspring and even multiply within it. They are carried inside the vector and can be found in the haemolymph, suggesting transmission via the salivary glands. The likelihood of transmission is positively correlated with the duration of the acquisition and inoculation feeding periods. These viruses typically have a prolonged transmission threshold period and a latent period, although the latter is not always clearly defined. However, it should be noted that these additional characteristics should not be considered the only criteria for labeling a virus as “persistent.”