Is 'infectious' a synonym for contagious?

Answer 1

No, they are not synonymous.

In Biology, contagious diseases are spread by personal contact or communication from a sick individual to a healthy individual. They are spread through physical contact, through air droplets, and through fomites. In this way, contagious diseases are easily spread. Examples include the common cold, the flu, TB, and leprosy.

Infections are diseases that are caused by pathogenic microbial agents (bacteria, viruses, protozoa, fungi, worms and prions) that get into the body and cause problems. Some Infectious Diseases spread in the same way that contagions do. Others, however, are transmitted via bites from insects or animals. Others are acquired by ingesting contaminated food or water or other exposures in the environment.

Contagious diseases can all be considered infectious but not necessarily the other way around. Anthrax, for example, is infectious but not contagious. It is caused by Bacillus anthracis and is transmissible through the contact with spores in soil and other reservoirs, infected hides or other animal products.

Speaking in general, they are not the same. In figurative terms, the word, infectious is used to describe something irresistibly catching: her laughter is infectious and brightens up the room. Figuratively, the word, contagious is used to describe something that spreads rapidly: his excitement is contagious and everyone joins in.