Microbes and Diseases

Microbes and Diseases

Disease (dis = against; ease = comfort) can be defined as an impairment or malfunctioning of the normal state of the living organism that disturbs or modifies the performance of vital functions of the body. Disease can be categorized based on:

i.  The extent of occurrence (endemic, epidemic, pandemic or sporadic).

 ii.  Whether infectious or non-infectious.

iii.  Types of pathogen – whether caused by bacterial, viral, fungal or protozoan infections.

iv.  Transmitting agent – whether air borne, water borne or vector borne.

1. Classification of disease based on occurence

Endemic: When the disease is found in a certain geographical area affecting a fewer number of people (low incidence). e.g. Occurrence of goitre in Sub-Himalayan regions.

Epidemic : When the disease breaks out and affects large number of people in a particular geographical region and spreads at the same time. e.g. Influenza.

Pandemic: When the disease is widely distributed on a global scale. e.g. Acquired Immunodeficiency Syndrome (AIDS).

Sporadic: When there is an occasional occurrence of a disease. e.g. Malaria and Cholera.

2. Manifestation of Disease

Communicability of diseases

Infectious diseases are communicable diseases. They are caused by external factors like pathogenic organisms (bacteria, virus, vectors, parasites) invading the body and causing diseases. e.g. Influenza, Tuberculosis, Chickenpox, Cholera, Pneumonia, Malaria, etc

Non-infectious disease are non-communicable diseases. They are caused by internal factors like malfunctioning of organs, genetic causes, hormonal imbalance and immune system defect. e.g. Diabetes, Coronary heart diseases, Obesity, Cancer, Goitre, etc

Point of entry and place of infection

The disease causing microbes enter the body through different means. An infection develops when these pathogens enter the human body through contaminated air, water, food, soil, physical contact, sexual contact and through infected animals. They may be organ specific or tissue specific within our body where microbes reside.

Reservoir of infection

Reservoir of infection refers to the specific environment in which the pathogens can thrive well and multiply without causing diseases. In other words, they are the breeding ground for pathogens. eg. Water, soil and animal population.

Incubation period

The interval between infection and first appearance of the diseases is called incubation period. It may vary from few hours to several days.

Infection and Illness

Infection is the entry, development or multiplication of an infectious agent in the human body or animals. An illness is due to a specific infectious agent, capable of being directly or indirectly transmitted from person to person, animal to animal or from the environment (through air, water and food) and insects (vectors).

3. Harmful effects of microbes

Pathogens cause disease in two ways. They are tissue damage and toxin secretion.

Tissue Damage: Many pathogens destroy the tissues or organs of the body causing morphological and functional damage. For example, bacterium of pulmonary tuberculosis damages the cells of the lungs, and virus causing hepatitis destroys liver tissue.

Toxin Secretion: Many pathogens secrete poisonous substances called toxins which cause diseases. Exotoxins are directly secreted by the pathogens. Endotoxins are released by the disintegration of pathogens.

Let us now study the causative organism, mode of infection, occurrence, symptoms and preventive measures of a few airborne, waterborne, vectorborne and sexually transmitted diseases.