These are spread by following means :
A Directly :
1. By hreet contact of infected person to healthy person.
2. By cough, sneezing, sputum, talking etc.
3. By coming in contact with just, allogic particle.
4. By the bite of any animals.
5. Through placenta from mother to developing. Joetus.
B. Intirectly :
1. By disease carrier or vector. For ag - Anopheles (female mosquits) spreats plasmotium from a person sulfering from Malaria to healthy perosn.
2. Through unchleanel hants and jingers.
3. Through invasion by pathogens.