The interaction between host and infecting organism plays an important role in the survival of both of these components. The mechanisms whereby survival of one, or both, is achieved can be considered at various anatomical levels and degrees of complexity; those involving whole tissues together with events occurring at the cellular and subcellular levels. The involvement of sequestration, or the ‘standing apart’ of an invading organism from the host, as a mechanism of survival can also be examined at these various levels.