Microorganisms can cause contagious diseases. For example, bacteria, fungi, virus and protozoa.
They can transmit from one place to another.
We can take the example of the situation now. Corona is caused by a virus which is a highly contagious disease. Also, we can assume examples like tuberculosis caused by bacteria.
Multicellular organisms might sometimes act as carriers of diseases. For example, Female Anopheles mosquito spread malaria.
