【Infectious】 , 【contagious】 , 【communicable】 , 【catching】 in their basic use as applied to diseases are distinguishable though closely similar in meaning.
【Infectious】 designates a disease resulting from the invasion of and multiplication in the body by germs (as bacteria, protozoans, or viruses) that produce toxins or destroy or injure tissues.
【Contagious】 more precisely designates an 【infectious】 disease caused by receiving living germs directly from a person afflicted with it or by contact with a secretion of his or some object he has touched.
【Communicable】 in this relation is nearly equivalent to 【infectious】 , but it emphasizes the transmissibility of the disease rather than the method by which it is acquired. 【Catching】 , a less formal term, is close in meaning to 【contagious】 , but it implies even more the dangers of contact.
【Infectious】 , 【contagious】 , and 【catching】 all have extended use but in such use the fine distinctions exhibited in their technical senses are not carried over with the result that they are nearly exact synonyms meaning rapidly imparted to others; thus, one may speak of 【contagious】 , or 【infectious】 , enthusiasm or of enthusiasm that is 【catching】 .
