Properties of Hazards Image Map

(Click on the links above or at the bottom of this page for the specific lessons)

All infectious agents (viruses, bacteria, protozoa and fungi) have the ability to reproduce, survive in the environment, to be transmitted to their hosts, to survive host defenses and to cause disease.

The diagram shown below illustrates the common life cycle of infectious agents, each having different durations for their periods of latency, incubation and communicability


  • Latent Period (latency) – The time from initial infection until the start of infectiousness.

  • Incubation Period – The time from the initial infection until the onset of clinical symptoms.

  • Period of communicability – The period during which an individual is infectious and can spread to other hosts.


While different infectious microorganisms share certain common characteristics there are far more differences than there are similarities.  Understanding the differences between the various types of infectious agents increases our ability to protect ourselves from infection and to recover from infections that do occur.   Click each of the links below to study the differences in some of the most common infectious agents.

Bacteria | Viruses | Protozoa | Fungi