Abstract
This chapter examines the effect of viruses in inducing modifications in chromosomes, immune system interactions, and cell metabolism to support such a hypothesis that virus may no longer be present when the pathology appears. When vaccines were available to protect the population against the major epidemics, then chronic, recurrent, or persistent infections came into focus. Viruses are everywhere and all organisms are permanently exposed to them. The result of this contact depends on the particular moment a t which a given cell is exposed to the virus. Rubella, for example, provokes a very benign disease in adults, but can induce abnormalities in the differentiating fetus. Although interferon is active against virus aggression, excess interferon has a toxic effect and can block differentiation. The capacity of several viruses to act as cellular mutagens by modifying chromosomes is well established, whatever the molecular mechanism may be. Mutations at the cellular level were carefully analyzed for their tumorigenic potential.
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