Introduction to Common Diseases
Designed as a quick‑reference guide for students, health‑care trainees, and anyone looking for a clear overview.
1. What Is a “Disease”?
| Aspect |
Definition |
| Disease |
A disruption of normal physiological function caused by internal (genetic, metabolic) or external (infectious agents, environmental) factors. |
| Signs |
Objective evidence observed by a clinician (e.g., fever, rash). |
| Symptoms |
Subjective experiences reported by the patient (e.g., pain, fatigue). |
| Etiology |
The cause(s) of a disease – can be infectious, genetic, autoimmune, nutritional, toxic, or multifactorial. |
| Pathogenesis |
The biological mechanisms that lead from the cause to the disease manifestation. |
| Epidemiology |
Study of disease distribution (incidence, prevalence) and determinants in populations. |
2. Classification of Common Diseases
| Category |
Typical Examples |
Key Features |
| Infectious diseases |
Influenza, tuberculosis, COVID‑19, malaria |
Caused by pathogens (virus, bacteria, protozoa, fungi). Transmissible; often preventable by vaccination or hygiene. |
| Chronic non‑communicable diseases (NCDs) |
Hypertension, type 2 diabetes, coronary artery disease, chronic obstructive pulmonary disease (COPD) |
Long‑lasting, progressive, often linked to lifestyle, genetics, or environmental exposures. |
| Genetic / congenital disorders |
Cystic fibrosis, sickle‑cell disease, Down syndrome |
Result from inherited DNA mutations or chromosomal abnormalities. |
| Autoimmune diseases |
Rheumatoid arthritis, systemic lupus erythematosus, multiple sclerosis |
Immune system mistakenly attacks self‑tissues. |
| Nutritional deficiencies / excesses |
Iron‑deficiency anemia, scurvy (vitamin C deficiency), obesity |
Imbalance of essential nutrients; can be prevented/treated with diet modification. |
| Neoplastic diseases |
Breast cancer, leukemia, melanoma |
Uncontrolled cell growth; may be benign or malignant. |
| Environmental / occupational diseases |
Asbestosis, lead poisoning, silicosis |
Result from exposure to toxic substances or physical agents. |
3. Core Concepts Across Diseases
3.1. Transmission & Prevention (Infectious)
| Mode of transmission |
Examples |
Primary preventive measures |
| Respiratory droplets |
Influenza, COVID‑19 |
Masks, ventilation, vaccination |
| Airborne |
Tuberculosis, measles |
Negative‑pressure rooms, N95 respirators, immunization |
| Vector‑borne |
Malaria (mosquito), Lyme disease (tick) |
Vector control, repellents, prophylactic meds |
| Fecal‑oral |
Hepatitis A, cholera |
Hand hygiene, safe water, sanitation |
| Direct contact |
Herpes simplex, MRSA |
Barrier protection, wound care |
3.2. Risk Factors (Chronic NCDs)
| Modifiable |
Non‑modifiable |
| Tobacco use, unhealthy diet, physical inactivity, excessive alcohol, obesity |
Age, sex, family history, genetics, ethnicity |
3.3. Diagnostic Approach (Universal)
- History – chief complaint, timeline, exposures, family history.
- Physical examination – systematic organ‑system review.
- Laboratory tests – CBC,