Escape Mechanisms in Schistosomiasis

Abstract

Survival and growth of infectious organisms in the face of the immune response mounted by their immunocompetent hosts is made possible through one of two strategies: one is to outrun rejection by fast replication and/or mutation, as observed in some bacterial or viral infections; the other is to impair development or expression of immunity so as to evade the deleterious consequences of the host’s counter-attack. Indeed, it is now recognized that in most infections, it is the infectious organism, that determines whether or not to allow itself to be rejected by immune effectors. This is clearly the case of parasites which in general induce chronic infections and are thus confronted for months and often years with the immune response that they have to maintain within limits compatible with both their own survival and that of their mammalian hosts. This leads in many instances to the refined elaboration in these organisms of a complex network of processes allowing them to escape the defence mechanisms of their host. Such a complexity gives the expression of immunity in parasitic diseases a dynamic aspect reflecting the permanent balance between effector and regulatory mechanisms (Capron and Dessaint, in press).