I have always been slightly confused over the differences between the words ‘infectious’ and ‘contagious’. I have heard them being used interchangeably but I wasn’t certain as to whether this was correct.
In short, it depends on the disease; an infectious disease is one that is transferred by micro-organisms in the air or in water and contagious diseases are transmitted by physical contact.
Infectious diseases are caused by pathogenic microbes (bacteria, viruses, parasites or fungi) which enter the body and cause problems. Many diseases fall under the category of being infectious and contagious- this is when the bacteria of the infectious disease is spread from person to person.
Contagion is considered to be measured on a scale with different diseases being highly contagious or not very contagious (eg. the flu is highly contagious as the virus can pass simply by touching or sharing objects. Ebola is said to be much less contagious).