Unlike some other viruses, like barley yellow dwarf virus, PPV is not persistent in the aphid and is transferred from the mouthparts of the aphid between plants. Long distance spread usually occurs as a result of the movement of infected nursery stock or propagative materials. Once a plant is infected the virus is systemic and occurs in the cytoplasm of cells from all parts of the plant. When a host tree is infected by plum pox, the infection eventually results in severely reduced fruit production, and the fruit that is produced is often misshapen and blemished. The presence of plum pox can also enhance the effects of other endemic viruses infecting various species of the genus "Prunus", such as prune dwarf virus, Prunus necrotic (browning) ringspot virus, and apple chlorotic (yellowing) leaf spot virus, resulting in still greater economic losses. In peach, infected trees may exhibit color-breaking symptoms in the blossoms. This appears as darker pink stripes on the flower petals and can be useful for early season surveys. Symptoms can be present in young leaves in the spring and /or on developing fruit. Some trees show no symptoms on leaves or fruit. Not all infection in "Prunus" are characterized by a ring symptom on leaves. Several cultivars show yellowing line patterns and blotches, or necrotic ring symptoms on expanded leaves. Leaf distortion has also been observed. Infected fruit can develop yellow rings or blotches, or brown rings, and some plum and apricot fruit can be severely deformed and bumpy. The seed of many infected apricots and some plums show rings. Many non-"Prunus" species, in at least nine plant families, have been infected artificially with one or more strains of the plum pox virus, and in some cases found naturally infected in the field. The maintenance of the virus in non-"Prunus" species complicates disease management. No cure or treatment is known for the disease once a tree becomes infected. Infected trees must be destroyed. Once the disease becomes established, control and prevention measures for plum pox include field surveys, use of certified nursery materials, control of aphids, and elimination of infected trees in nurseries and orchards. Sources of resistance exist in "Prunus", but are not common. A team of scientists from the United States and France has genetically engineered a plum pox-resistant plum called C5, and the resistance can be transferred through hybridization to other plum trees.