Unlike harmless microorganisms some microorganisms, are harmful; they can make the host cell (plant, animal or human being) unwell. In the previous objects, we provided in-depth knowledge on the concepts of various microorganisms, characteristic features, and structure. This topic will be dedicated to Microbes and disease, where we can explore the different types of illness in great detail.
Any functional or physical change from the normal state that causes discomfort, disability, or impairs a living organism's health is called a disease.
Meaning of health: Its described as a state of complete physical, mental and social well being is known as health. This is according to the WHO.
What is disease: Health is a state of proper functioning of body and mind. All the body functions are interconnected. Anything that stops the proper functioning of cells and tissues will lead to a lack of appropriate body functioning. Various agents can cause this malfunctioning at the level of cells, tissues, organs or organ systems.
  • The unicellular or multicellular organisms that cause infection are called infectious agents.
  • Some microorganisms can cause diseases in human beings, animals and plants; such disease- causing organisms are called pathogens.
  • The study of disease is called pathology.
The biological agents such as viruses, bacteria, fungi, protozoa or stress, and any other immune system failure led to the state of illness and health failure. This condition is known as disease (dis = against; ease = comfort). In the presence of a disease, functioning, or the appearance of body system may change. These changes give rise to symptoms and sign of disease.
Symptoms of diseases are the general indications that we feel as wrong or uneasy such as cold, headache, cough, vomiting, diarrhoea, etc. These all are the symptoms indicating a disease, but they do not precisely show the condition. For example, a stomach ache may rarely mean abdominal cancer; it merely means just due to stress or any digestion problem.
There are two types of diseases based on the way it is formed.
  1. Infectious disease (Communicable)
  2. Non-infectious diseases (Non-communicable)
1. Infectious Disease:
Infectious diseases are diseases created through infectious agents such as bacteria, viruses, fungi etc. These are the diseases caused by external pathogenic organisms that invade our body and can be transferred from human to human or animal to animal through air, water or food .
Hence the diseases are called infectious diseases.
Video explaining the transmission of communicable diseases
Influenza, Tuberculosis, Chickenpox, Cholera, Pneumonia, etc.
2. Non-Infectious diseases:
These diseases are caused due to a malfunction in the body system. Pathogens do not cause them. So these diseases don't get transferred from one organism to others. Hence the conditions are called non-infectious diseases (NCD).
Video explaining the transmission of non - communicable diseases
They are caused by,
  • Malfunctioning of organs
  • Genetic abnormalities
  • Hormonal imbalances
  • Immune system defects
Diabetes, Obesity, Cancer, Goitre, Coronary heart diseases, etc.
Pathogens that cause disease can enter our bodies in a variety of ways. Some of these are discussed further below. Based on this, diseases are classified into
  1. Airborne disease
  2. Waterborne disease
  3. Vector-borne disease
  4. Sexually transmitted disease