
Tapeworms, for instance, can reach a length of 6 meters (20 feet).įood and water are the most common sources of parasite and invading organism transmission.

They have so few genes and proteins of their own that in order to reproduce they need to commandeer the machinery of the cells they invade. VIRUSES are the smallest of all infectious agents, averaging about 100 nanometers (100 billionths of a meter) in length.

The approximate sizes of microbes can be approximated by using the following rule of thumb:
