Ecology and Epidemiology

- Survival and virus reservoirs
 
Tobacco mosaic virus (TMV) is a particularly infectious and persistent virus. Unlike almost all viruses, which are obligate parasites, it is able to survive in the soil for several years, in leaf waste and roots, and in infected nurseries. The first infections usually take place in the nursery, for example by contaminated soil or tools. The infections also occur in a field by root contact between the colonising roots of plants and those remaining from a previous tobacco crop or another susceptible host. Actually the virus is able to infect more than 190 plants that contribute to its propagation and conservation.
 
 
- Transmission and dissemination
 
This virus is easily and essentially transmitted by contact. A simple contact from plant to plant, with hands, clothing or contaminated tools is sufficient for transmission. It is easy to understand why the activities of workers and agricultural operations carried out in fields greatly influence the epidemiology of this virus. Seed transmission does not seem possible in tobacco, which is not the case for other Solanaceae plants (tomato, pepper) that can also be infected by TMV. Several chewing insects may transfer the virus when consuming healthy or diseased leaves; but their efficacy as agents of transmission is practically zero. Other insects, typically reported as virus vectors, do not transmit TMV. Its spread can be assured by contaminated plants, but also by workers and their tools, or technicians moving from a contaminated crop to a healthy one.