-Priyanti, Subject Matter Expert at Edumarz
Solution: Communicable or infectious diseases can spread in numerous ways, which are broadly classified as direct and indirect transmission. In the former case, a healthy person directly contacts the pathogens from an infected person without the involvement of any intermediate agent. Indirect transmission requires such an agent for a healthy person to develop a disease; it cannot spread directly from the reservoir of infection to the host.
Direct transmission:
Some diseases occur upon direct contact with an infected person, eg. leprosy, chicken pox, syphilis, measles, etc.
Some diseases are spread through droplet infection, eg. common cold, influenza, diphtheria, whooping cough, etc.
Diseases like tetanus are spread upon contact with soil; their cysts are spread throughout the soil and are taken up by the body through cuts and wounds.
Animal bites cause certain diseases such as rabies, which occurs after being bitten by dogs.
Transplacental transmission is also an instance of direct transmission, where infected mothers pass their disease into the fetal blood through placenta. Eg. virus of German measles, bacteria of Syphilis, etc.
Indirect transmission:
Vector-mediated diseases are the common mode of indirect transmission. Eg. mosquito-borne malaria and dengue, housefly-mediated cholera, typhoid, etc.
Pathogens may be transmitted through contaminated needles, towels, handkerchiefs or utensils. Eg. influenza, AIDS, etc.
Some diseases are contracted through contaminated food and water. Eg. cholera, hepatitis B, etc.
Pathogens such as epidemic typhus are airborne and spread by wind and aerosol sprays.
Transmission may also occur through handling food with unclean hands, eg. amoebiasis, enterobiasis, etc.