Circulative viruses : persistent transmission

The transmission of circulative viruses has been particularly well described in the Luteoviridae. Once the aphid has ingested the viral particles they flow into the cavity of the digestive tube with the phloem sap as far as the mid- or distal part of the-intestine. When the virus arrives near these tissues, the virus crosses the first epithelial barrier to enter the insect’s general cavity (haemocoel). In this compartment, the viruses appear to fix onto a protein synthesized by the aphid’s endosymbiotic bacteria. This virus-protein interaction is thought to provide the viral particles with protection against the insect’s immune system.

The viruses diffuse into the haemocoel from the hind region of the aphid upto cells in the salivary glands which they pass through a second time where they mix with the fresh salivary secretions. This mixture with the viral particles will be released in the plant’s phloem tissues. In this process involving circulative viruses, the aphid remains infectious for a long time, even beyond moulting. This transmission process, known as the persistent mode, involves a close, highly specific interaction between the virus and its vector.

transmission of the moderate beet yellow virus 
by Myzus persicae