When you have studied this session, you should be able to:

• Define and use correctly all of the key terms printed in bold.
• Identify the main types of infectious agents.
• Describe the main reservoirs of infectious agents.
• Describe the chain of transmission of communicable diseases and explain how infectious agents are transmitted by direct and indirect modes.
• Describe the characteristics of susceptible hosts and the main risk factors for development of communicable diseases.
• Describe the stages in the natural history of communicable diseases.