Here are five common causes of communicable diseases:

1. Bacteria:

   These are single-celled organisms that can cause infections such as strep throat, urinary tract infections, and tuberculosis.

2. Viruses:

   Viruses are smaller than bacteria and cause a multitude of diseases, ranging from the common cold and influenza to more severe conditions like HIV/AIDS and COVID-19.

3. Fungi:

   Fungi can cause skin infections like athlete's foot and ringworm, as well as more serious systemic infections, especially in individuals with weakened immune systems.

4. Parasites:

   Parasites are organisms that live on or in a host and obtain nutrients from it. They can cause diseases like malaria, giardiasis, and toxoplasmosis.

5. Prions:

   Prions are misfolded proteins that can cause rare and fatal neurodegenerative diseases known as transmissible spongiform encephalopathies (TSEs). An example is Creutzfeldt-Jakob disease.