Classification of General Causes of Disease

• Also known as aetiology/aetiological factors, they are majorly classified into two:

1. Endogenous Causes

These are primarily genetic disorders, such as:

• Genetic disorders/mutations, may be:

  • Determined; i.e., born with them / congenital

  • Epigenetics; involving the way environmental factors influence expression of genes

• Chromosomal disorders

• Autosomal dominant

• Autosomal recessive

2. Exogenous Causes

These are primarily from environmental factors; they include but are not limited to:

• Infections: bacteria, viruses, etc.

• Chemical toxins: e.g., heavy metals like lead, mercury

• Physical agents, such as: heat, cold, electric energy, radiation

• Malnutrition: either excess or under-nutrition

• Disorders of immunity, such as:

  • Immune compromise

  • Hypersensitivity (allergies)

  • Autoimmunity

• Degenerative diseases: commonly associated with increasing age

• Neoplasms: either benign or malignant

• Psychiatric: either psychotic (e.g., bipolar disorder) or neurotic (e.g., anxiety and depression)

• Psychosomatic: involving the interaction between the mind and the body in disease causation

• Iatrogenic: causes due to medical interventions

• Idiopathic: where the cause cannot be established

• Multi-factorial: involving a combination of more than one group of factors

Causes of Disease: Infectious vs Non-Infectious

Infectious Causes

All diseases caused by microorganisms called pathogens, which can spread from one person to another — hence, such diseases are called communicable diseases.
The pathogens include:

• Bacteria

• Viruses

• Fungi

• Protozoans

• Worms

• Rickettsia

Examples of infectious diseases include:

• Cholera

• Chickenpox

• Malaria

• Brucellosis

• Typhoid

Non-Infectious Causes

These are not primarily due to pathogens but rather other conditions or factors. They may not be spread from one person to another — hence, they are called non-communicable diseases.
Non-infectious causes include:

• Genetic mutations

• Metabolic disorders

• Malnutrition

• Autoimmune reactions

• Hypersensitivity / allergic reactions

• Toxic environmental exposures / unhealthy lifestyle choices