Question

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

Answer 1

The ways through which infections diseases spread are :
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, ring worm etc. are spread through physical contact with infected person or through articles of use.
(ii) 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) Animalbites : Communicable diseases can also spread through the animal bites. For examples, 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 foetus 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. The infected person throws out little droplets on sneezing coughing or spitting. Someone standing closely can breathe in these droplets and, thus, microbes get a change to start a new infection in this person. In crowded living conditions, the air borne diseases are likely to spread rapidly.
(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. Usually, a part of life cycle of the pathogen is passed in the body of the vector. Female mosquitoes of many species are vectors of several diseases. They require blood meal in order to obtain nutrients for laying eggs. Female Anopheles spreads malaria while Culex spreads filaria.