Class 8 Science

Harmful Microorganisms

Communicable Disease: A disease which can spread from one person to another is called communicable disease.

Infectious Disease: A disease which is caused by an attack from microbes is called infectious disease.


A microbe which causes disease is called a pathogen. Some examples of pathogens are as follows:

Pathogens and Diseases

PathogenDiseaseMode of Transmission
PlasmodiumMalariaSpreads through bite of female Anopheles mosquito.
Dengue virusDengueSpreads through bite of Aedes mosquito.
Common cold virusCommon coldThrough air; when someone coughs or sneezes.
Many bacteriaCholera, diarrhoeaThrough contaminated food and water.
Hepatitis B virusHepatitis BThrough exchange body fluids.
HIVAIDSThrough exchange of body fluids.
Bacillus anthracisAnthrax (in animals)Through contact.

How to prevent Malaria and Dengue:

Diseases caused by microbes in plants
MicrobesDiseaseMode of transmission
BacteriaCitrus cankerAir
FungiRust of wheatAir, seeds
VirusYellow vein mosaic of OkraInsects