Communicable Diseases
NCERT Class 9 • Science • Chapter "Why do we Fall Ill" | NCERT Class 8 • Science • Chapter "Microorganisms Friend and Foe"
Communicable Diseases
A communicable or infectious disease is caused by a pathogen and spreads from one person to another. Knowing the causative organism matters practically, because the treatment for a bacterial disease will not work against a viral one.
Types by Causative Organism
- Bacterial diseases include tuberculosis, typhoid, cholera, tetanus, plague, diphtheria, whooping cough and leprosy.
- Viral diseases include influenza, common cold, measles, chickenpox, polio, rabies, dengue, hepatitis and AIDS.
- Protozoan diseases include malaria, caused by plasmodium, and amoebic dysentery, caused by entamoeba.
- Fungal diseases include ringworm and athlete's foot, which affect the skin.
- Worm infections such as those caused by roundworm and tapeworm spread mostly through contaminated food and water.
- Antibiotics work against bacteria but not against viruses, which is why they should not be taken for a common cold.
- Overuse of antibiotics creates resistant bacteria, which is now a serious public health problem.
Modes of Spread and Prevention
- Air spreads tuberculosis, influenza, measles and the common cold through droplets from coughing and sneezing.
- Water and food spread cholera, typhoid, hepatitis and amoebic dysentery.
- Vectors spread disease: the female anopheles mosquito carries malaria and the aedes mosquito carries dengue and chikungunya.
- Direct contact spreads skin infections, and body fluids spread hepatitis B and AIDS.
- Prevention rests on clean drinking water, sanitation, personal hygiene, safe food and vector control.
- Vaccination gives specific protection and has been the decisive tool against smallpox and polio.
- Early diagnosis and completing the full course of treatment prevent both relapse and the spread to others.
- Non communicable diseases such as diabetes, high blood pressure, heart disease and cancer do not spread from person to person.
- These are linked to lifestyle, so exercise, balanced diet and avoiding tobacco and excess alcohol reduce the risk.
- Good general health, adequate nutrition and clean surroundings lower the chance of falling ill in the first place.
- Public health measures therefore matter more than individual treatment, since they stop disease before it starts.
| Disease | Caused By | Spread Mainly By |
|---|---|---|
| Tuberculosis | Bacterium | Air |
| Malaria | Protozoan | Female anopheles mosquito |
| Dengue | Virus | Aedes mosquito |
| Cholera | Bacterium | Contaminated water |
Vector — an organism such as a mosquito or housefly that carries a pathogen from one host to another.
Exam me kaise aata hai
- Malaria is caused by which organism — plasmodium, a protozoan
- Dengue is spread by which mosquito — aedes
- Which disease is caused by a virus — polio
- Antibiotics are effective against — bacteria
UPSC/State PSC ke liye
- Antibiotics do not work against viruses because viruses use the host cell's machinery, which the antibiotic cannot attack without harming the host.
- Vector control works on the breeding site, since removing stagnant water is cheaper and more effective than treating each case.
Yahan confuse hote hain
✗ Antibiotics cure viral fever | Antibiotics work only against bacteria | ✓
✗ Malaria is caused by a virus | Malaria is caused by a protozoan | ✓
✗ Dengue and malaria are spread by the same mosquito | Dengue by aedes, malaria by female anopheles | ✓
Ek nazar me
- Diseases are bacterial, viral, protozoan, fungal or worm caused.
- Antibiotics work on bacteria only; overuse creates resistance.
- Spread happens by air, water, food, vectors, contact and body fluids.
- Clean water, sanitation, hygiene, vector control and vaccination prevent them.