This chapter discusses the ways in which viral replication damages tissues and organs and the ways in which the body's own responses may cause damage. It presents examples illustrating the pathogenesis of four basic kinds of acute viral infection: respiratory, intestinal, generalized, and neurological. As the immune system plays a key role in protection against infections, viral damage to its components can exacerbate the severity of disease or predispose to superinfection with other viral or nonviral agents. Both specific acquired immunodeficiency and generalized immunosuppression can occur in viral infections. The immune response to viral infection may itself frequently contribute to the pathology of the disease. Inflammation with accompanying cellular infiltration is a regular feature of viral infection. Such common signs as erythema, edema, and enlargement of lymph nodes have an immunological basis. There are viral diseases in which the cardinal manifestations are caused by the body's immune response. Immunopathological (hypersensitivity) reactions are traditionally classified into types 1, 2, 3, and 4. For most viral infections, it is not known whether immunopathological effects make a significant contribution to disease and if so then as to which of the four classical hypersensitivity reactions is implicated. It is instructive to speculate about the possible involvement of different kinds of hypersensitivity reactions in viral diseases.
Mechanisms of Disease Production: Acute Infections