State the common methods of transmission …

Means of spread of Infectious disease

1)Air-borne diseases:Microbial agents can move from an affected person to someone else through air.

It occurs through the little droplets thrown out by an infected person who sneezes or coughs.

Someone standing close by can breathe in these droplets, and microbes get chance to start a new infection.
For Example :Common cold, pneumonia, tuberculosis

2)Water-borne diseases:They can be spread through water.

If the excreta from someone suffering from an infectious gut disease such as cholers or amoebiasis gets mixed with drinking water used by people living nearby.

The cholera infected bacteria will enter new hosts through the water they drink and cause disease.

3)Sexually Transmitted diseases(Syphilis,AIDS):These diseases are transmitted by sexual contact from one partner to other.However these diseases are not transmitted by causal physical contact.
AIDS virus can also spread through blood to blood contact with infected people or infected mother to her baby during pregnancy or breast feeding.

4)Through vectors:Vectors are carrier of a disease or infection.
Many animals which live with us may carry disease.These animals carry infecting agents from a sick person to another host.