Question
Distinguish between communicable (infectious) and non-communicable diseases. Give three examples of each and briefly explain their causes and modes of spread/origin.
Solution — Step by Step
Communicable diseases (also called infectious diseases or contagious diseases) are caused by pathogens — microorganisms or biological agents — that can be transmitted from one host to another. The defining characteristic is transmissibility: the disease-causing agent spreads, either directly (person to person) or indirectly (through vectors, contaminated water/food, or air).
The causative agents include: bacteria, viruses, fungi, protozoa, helminths (worms), and prions.
1. Tuberculosis (TB) — Caused by Mycobacterium tuberculosis (bacterium). Transmitted through airborne droplets when an infected person coughs or sneezes. Primarily affects lungs. Can be treated with antibiotics (though MDR-TB is a growing concern).
2. Malaria — Caused by Plasmodium species (protozoan — P. falciparum, P. vivax, etc.). Transmitted through the bite of an infected female Anopheles mosquito (vector-borne disease). Classic symptoms: cyclic fever and chills as parasites burst from red blood cells.
3. Influenza (flu) — Caused by Influenza virus (types A, B, C). Transmitted via respiratory droplets and aerosols. Highly variable — the virus mutates its surface proteins rapidly, which is why a new flu vaccine is needed each year.
Non-communicable diseases (NCDs) are not caused by infectious agents and cannot be transmitted from one person to another. They arise from a combination of genetic factors, lifestyle choices, environmental exposure, and age-related changes.
NCDs are the leading cause of death globally — responsible for ~74% of all deaths worldwide (WHO data). They are often chronic, long-duration conditions requiring long-term management rather than cure.
1. Type 2 diabetes mellitus — Caused by insulin resistance (cells fail to respond to insulin) and/or insufficient insulin production. Risk factors: obesity, physical inactivity, high-sugar diet, genetic predisposition. Cannot be transmitted. Managed with diet, exercise, oral hypoglycaemics, or insulin injections.
2. Cardiovascular disease (e.g., coronary artery disease) — Caused by accumulation of atherosclerotic plaques (cholesterol, fat, calcium) in coronary arteries, restricting blood flow to the heart. Risk factors: high blood pressure, smoking, high LDL cholesterol, diabetes, obesity, stress. Leads to heart attacks and strokes.
3. Cancer (e.g., lung cancer) — Caused by uncontrolled cell division due to mutations in proto-oncogenes and tumour suppressor genes. Lung cancer is strongly associated with smoking (carcinogens in tobacco cause DNA mutations). Can also be triggered by radiation, chemical carcinogens, and sometimes viruses (HPV → cervical cancer is an exception linking to infectious agents, but the cancer itself is not contagious).
| Feature | Communicable Diseases | Non-Communicable Diseases |
|---|---|---|
| Cause | Pathogens (bacteria, virus, etc.) | Lifestyle, genetics, environment |
| Transmissibility | Can spread person to person | Cannot spread |
| Examples | TB, malaria, flu, cholera, AIDS | Diabetes, cancer, heart disease |
| Treatment | Antibiotics, antivirals, antiparasitics | Management, lifestyle change, surgery |
| Prevention | Vaccines, hygiene, vector control | Healthy lifestyle, screening |
| Duration | Usually acute (short-term) | Often chronic (long-term) |
Why This Works
The classification into communicable vs non-communicable is primarily about aetiology (cause) and epidemiology (how it spreads in populations). Public health strategies differ radically:
- For communicable diseases: interrupt transmission chains (quarantine, vaccination, vector control, sanitation)
- For non-communicable diseases: modify risk factors (promote healthy diet, physical activity, reduce tobacco/alcohol, manage hypertension)
Understanding this distinction helps you critically evaluate news about disease outbreaks and health policy.
Alternative Method — Classification by Causative Agent
Another way to classify diseases:
- Genetic diseases: inherited mutations (haemophilia, sickle cell anaemia, PKU)
- Nutritional deficiency diseases: lack of vitamins/minerals (scurvy, rickets, anaemia)
- Degenerative diseases: age-related deterioration (Alzheimer’s, arthritis)
- Mental diseases: depression, schizophrenia All of these are non-communicable.
Common Mistake
Students sometimes classify AIDS (HIV infection) as non-communicable because it is not “spread through air like flu.” HIV is definitely communicable — transmitted through blood, sexual contact, and mother-to-child. Communicable diseases are not limited to airborne transmission; they include any disease where the causative agent transfers from host to host by any route.
Also, do not say “all cancers are non-communicable.” While most cancers are not infectious, some cancers are strongly associated with infectious agents: HPV → cervical cancer, H. pylori → stomach cancer, hepatitis B virus → liver cancer. The cancer itself doesn’t spread, but the predisposing infection can.
NEET tests this topic as MCQs on: (1) mode of transmission of specific diseases (Malaria = mosquito vector; TB = airborne; typhoid = contaminated food/water); (2) which of the following is non-communicable — always look for lifestyle/genetic diseases; (3) which organism causes a named disease. Learn the pathogen-disease pairs: Plasmodium → malaria; Mycobacterium → TB; Vibrio cholerae → cholera; HIV → AIDS.