Different means by which infectious diseases are spread are:
(i) Through air: When an infected person sneezes or coughs small droplets are thrown out.
(ii) Through water: This occurs if the excreta from someone suffering from an infectious gut disease, such as cholera, get mixed with the drinking water used by people living nearby.
(iii) Through physical contact: Casual physical contacts include handshakes or hugs or sports, like wrestling, or by any of the other ways in which we touch each other socially.
(iv) Through vectors: These animals carry the infecting agents from a sick person to another potential host. These animals are thus the intermediaries and are called vectors.