Following are the modes of transmittance of infectious diseases:

(i) Air- Certain microbes travel in air and are inhaled by human beings, causing various infectious diseases such as common cold, pneumonia and tuberculosis.

(ii) Water- Infectious diseases spread via water when the stool of an infected person gets mixed in drinking water of a locality. Cholera is an example of water-borne diseases.

(iii) Sexual contact- Some infectious diseases such as syphilis and AIDS spread via sexual contact between a normal person and an infected person.

(iv) Vectors- Many animals are the carriers of various pathogens that cause infectious diseases and behave as vectors. Malaria is an example of such disease, in which female mosquito is the vector of the malaria-causing parasite.