Class 8 Biology Microorganisms: Friend and Foe Harmful Micro-organisms

Harmful Micro-organisms

There are many microbes which cause several diseases in plants, animals & human beings. Such disease-causing organisms are called Pathogens.  Pathogens include bacteria, viruses, fungi & protozoa.


In this section, we will discuss about the various diseases caused by various pathogens. ‘Disease’ is a disturbed ease. Disease results in a change in either the functioning or the appearance of one or more systems of the body for worse.

Diseases in Humans: Typhoid

  • Pathogen
    • Bacteria, Salmonella typhi


  • Pathogen’s entry
    • Contaminated food & water
    • Primarily reach small intestine


  • Symptoms
    • High fever
    • Headache
    • Weakness
    • Stomachache
    • Constipation
    • Loss of appetite


  • Treatment
    • Diagnosed using Blood culture/ Urine culture or Widal test
    • Treated with a course of antibiotic medication

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