The application of system theory (or more precisely, differential equa
tions) to immunology and disease, in general, is presented here, Parti
cular results from U.S.-Russian research collaboration depict the pote
ntial role of such systematic analysis for more effective health care
and disease control. In particular, some emphasis is given to control
of influenza. After a brief systematic overview of immunology, a simpl
e infectious disease model is developed to explain four basic forms of
disease: subclinical, acute, lethal and chronic. Then, disease treatm
ent is studied.