Infectious diseases can be spread by following ways:
(a) By direct contact
(b) Through some medium
(a) By direct contact
Microorganisms travel from infected person to other person by sharing food in the same utensil, using the clothes of the patients, etc.
(b) Through medium
Microorganisms reach other people through various medium.
(i) Through air
When the patient coughs spits or excretes, many microorganisms spread in the air and through the breathing they reach other persons and make them infected.
(ii) Through contaminated food and water
Many diseases are spread due to contaminated water and food. Flies sit on open foodstuffs and contaminate them by leaving microorganisms on them. When this food is consumed by people they get infected and diseases like diarrhea, dysentery, etc. are caused.
(iii) Through insects
Mosquitoes carry many microorganisms with them. When they
bite a healthy person they leave these microbes in his blood and make him patient of malaria, dengue fever, etc.
(iv) Through carriers
Sometimes people have the microbes in them but they themselves are not patients but just carriers, i.e., they can infect other people by these microorganisms.
Infectious diseases have a definite period of their own. After that period, the disease dies out naturally. Once the person suffers from such disease, these microorganisms create immunity in the body of the patient for that particular disease. That is why there is very little possibility of the same disease happening again in his lifetime. Time span of the disease can be divided as under:
(i) Incubation period
This is the 1st stage of disease. In this stage, microorganism start growing and producing their toxins, but in this stage no external symptoms of the disease are visible. Every disease has its own incubation period.
(ii) Infection period
When the symptoms are visible in the body of the patient this is called infection period. It is divided into various stages:
(a) Onset of infection
(b) Period of climax
(c) Period of decline
(d) Period of convalescence
Sometimes the patient is so weak that he cannot take care of himself and is not properly cured. A microorganism again attacks the patient and makes him sick. This situation is very unfortunate as it can leads to grave complications. The patient may not sometime able to sustain it.