Types of Diseases

At the broadest level, all diseases can be divided into two master categories:

1. Infectious (Communicable) Diseases – caused by external microscopic organisms – known as pathogens – invading the body. They are capable of spreading directly or indirectly from one individual to another.

• Bacterial Diseases: Caused by single-celled prokaryotic bacteria. Many release specific toxins that damage body tissues.
  • Examples: Tuberculosis, Typhoid, Cholera, Tetanus.
• Viral Diseases: Caused by viruses that hijack a host cell’s machinery to replicate.
  • Examples: Influenza, Dengue, Common Cold, Rabies, COVID-19.
• Fungal Diseases: Caused by fungi, yeasts, or molds, typically affecting the skin, nails, or respiratory system.
  • Examples: Ringworm, Athlete’s foot, Candidiasis.
• Protozoan & Parasitic Diseases: Caused by single-celled eukaryotes (protozoa) or larger multicellular parasites (like worms).
  • Examples: Malaria (caused by the Plasmodium protozoan via mosquitoes), Amoebiasis, Ascariasis.

2. Non-Infectious (Non-Communicable) Diseases

These diseases cannot spread from person to person. They arise from internal factors such as genetic mutations, lifestyle choices, aging, or environmental exposures.

• Congenital & Genetic Diseases: Present right from birth. They are caused by structural development errors during pregnancy or inherited genetic abnormalities.
  • Examples: Down Syndrome, Hemophilia, Sickle Cell Anemia, Cystic Fibrosis.
• Degenerative Diseases: Characterized by the progressive deterioration of organs or tissues over time, often tied to aging or wear-and-tear.
  • Examples: Alzheimer’s Disease, Osteoarthritis, Parkinson’s Disease.
• Deficiency Diseases: Occur when the body lacks an adequate supply of essential dietary nutrients, vitamins, or minerals over an extended period.
  • Examples: Scurvy (Vitamin C deficiency), Rickets (Vitamin D deficiency), Anemia (Iron deficiency), Kwashiorkor (Protein deficiency).
• Cancerous (Neoplastic) Diseases: Triggered by uncontrolled, rapid cell division that leads to the formation of tumors capable of invading and destroying surrounding healthy tissues.
  • Examples: Leukaemia, Melanoma, Carcinomas.
• Immunological & Autoimmune Diseases: Occur when the body’s immune system experiences a malfunction. In autoimmune conditions, the immune system mistakenly attacks the body’s own healthy cells.
  • Examples: Rheumatoid Arthritis, Lupus, Type 1 Diabetes, severe allergies.

** Acute vs. Chronic diseases – Doctors also classify diseases by their duration and speed of onset:

⏱️ Acute Diseases: Come on suddenly and last for a very short duration (e.g., Influenza, Acute Appendicitis, Typhoid).

⏳ Chronic Diseases: Develop slowly over months or years, persist long-term, and often require lifetime management (e.g., Hypertension, Chronic Kidney Disease, Diabetes mellitus).