Bassocco

An infectious illness is the consequent clinical manifestation of an infection caused by microorganisms like: Bacteriae, fungi, virus, protozoos and prions. In the case of pathogen biological agents of macroscopic size, it is not called infection but infestation.

The infectious illnesses are divided in transmissible and not transmissible:

The transmissible infectious illnesses can spread directly from the infected individual, through the skin or mucous membranes or, indirectly, when the infected person contaminates the air by means of her breathing, an inanimate object or a food.

In the not transmissible infectious illnesses the microorganism is not transmites of an individual to other, but rather it requires some special circumstances, which may be environmental, accidental, etc., for its transmission. In these cases, infected people don't transmit the illness.