Highlight the ways through which infectious diseases generally spread in human communities.

Explanation

The ways through which infectious diseases spread are:
(a) Direct transmission : The pathogens are transmitted from an infected person to a healthy person directly without an intermediate agent. It occurs in the following ways:
(i)Physical contact with infected person : The pathogens of diseases like chicken pox, ringworm, etc. are spread through physical contact with infected person or through articles of use. Such diseases are called contagious diseases. Sexual contact : Few infectious diseases such as syphilis, gonorrhoea (both caused by bacteria) and AIDS (caused by virus) are transmitted by sexual contact from one partner to the other.
(iii) Contact with soil : Many pathogens can enter the human body from soil through injuries (e.g., tetanus).
(iv) Animal bites : Communicable diseases can also spread through the animal bites. For example, rabies virus enters the human body by the bite of rabid dog or monkey to cause rabies.
(v) Transplacental transmission : The diseases like AIDS, German measles and syphilis can also be transmitted from infected mother to the fetus through placenta.
Indirect transmission : It involves spread of pathogens of some diseases through some intermediate agents. Indirect transmission occurs in the following ways:
(i) Through air : Infectious microbes that cause common cold, tuberculosis, pneumonia, etc., can spread through air from infected persons on sneezing, coughing or spitting.
(ii) Through contaminated food and water : Cholera, hepatitis B, diarrhoea, ascariasis, etc., are some infectious gut diseases which are transmitted through contaminated food and water. Contamination comes from excreta of the infected person mixing up with drinking water and food directly or indirectly through flies).
(iii) Vectors : They are living organisms which spread the pathogens from an infected person to healthy person. E.g., Female Anopheles spreads malaria, Culex spreads filaria, etc.
(iv) Fomite borne : Articles coming in contact with infected persons also become sources of infection to healthy person(s), e.g., door handles, taps, utensils, garments and currency.