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How Communicable Diseases Spread
- All communicable diseases are caused by pathogens.
- Pathogens can enter through the air we breathe.
- They can also enter through dirty food or water.
- They spread by coughing, sneezing, or direct contact.
- Some spread by sharing personal items of a sick person.
Example 1 — Spread by Air
- A sick person coughs without covering the mouth.
- Germs float in the air and reach others.
- So the disease spreads through the air.
Example 2 — Spread by Mosquito
- A mosquito bites a sick person, then a healthy one.
- It carries the germs from one to the other.
- So mosquitoes spread diseases like malaria and dengue.
Important Points
- Insects like mosquitoes and houseflies that spread germs are called vectors.
- Worms that live inside our body and feed on us are called parasites.
Definition — Vectors
Vectors are insects like mosquitoes and houseflies that carry pathogens and spread disease.
Definition — Parasites
Parasites are organisms that live in or on another living being and feed on it.
Simple Steps to Prevent Communicable Diseases
- Keep ourselves and our surroundings clean.
- Wash hands with soap and water to remove pathogens.
- Cover the mouth and nose while coughing or sneezing.
- Wear a mask in crowded places and avoid sharing personal items.
- Stay home and rest when unwell to avoid spreading germs.
Example 1 — Handwashing
- A child washes hands before eating.
- This removes germs from the hands.
- So handwashing stops disease from spreading.
Example 2 — Wearing a Mask
- A person wears a mask in a crowded bus.
- The mask blocks germs from the air.
- So a mask protects against airborne diseases.
Important Points
- Clean food and water keep us safe from many diseases.
- Resting at home when sick protects others around us.
Definition — Prevention
Prevention means the simple steps we take to stop a disease before it happens.
Procedure
Grade 8 students listed common communicable diseases in Table 3.1. Check the details using books, trusted websites, or a teacher. Then think about steps to prevent each disease.
Table 3.1 — Some Common Communicable Diseases Affecting Humans
| Disease | Causal agent | Site of infection | Symptoms | Preventive measures |
|---|---|---|---|---|
| Diseases spread through the air | ||||
| Common cold and influenza | Virus | Respiratory tract | Nasal congestion and discharge, sore throat, fever, cough, body ache | Washing hands often, not sharing personal items, covering the mouth and nose |
| Chickenpox | Virus | Respiratory tract, skin | Mild fever, itchy skin, rashes, blisters | Complete isolation of the patient, covering the mouth and nose, vaccination |
| Measles | Virus | Skin, respiratory tract | Fever, sore throat, reddish rashes on neck, ears, and skin | Isolation of the patient, covering the mouth and nose, good hygiene, vaccination |
| Tuberculosis (TB) | Bacteria | Lungs | Cough, fever, fatigue, loss of appetite, night sweats | Avoiding close contact with TB patients, covering the mouth and nose, good hygiene, vaccination |
| Diseases spread through contaminated water and food | ||||
| Hepatitis A | Virus | Liver | Fatigue, fever, loss of appetite, nausea, vomiting, jaundice, upper-right abdomen pain | Drinking boiled water, vaccination |
| Cholera | Bacteria | Intestine | Diarrhoea and dehydration | Personal hygiene, good sanitation, cooked food, boiled drinking water, vaccination |
| Typhoid | Bacteria | Intestine | Headache, abdominal discomfort, fever, diarrhoea | Personal hygiene, good sanitation, cooked food, boiled drinking water, vaccination |
| Ascariasis (roundworms) | Worms | Intestine | Worms in stool, loss of appetite, poor growth, diarrhoea, weight loss, anaemia | Personal hygiene, good sanitation, cooked food, boiled drinking water |
| Diseases transmitted by insects | ||||
| Malaria | Protozoa | Skin, blood | High fever, profuse sweating, periodic chills | Mosquito nets and repellents, long-sleeved clothes, control of mosquito breeding |
| Dengue fever (Break bone fever) | Virus | Skin, blood | Fever, headache, muscle and joint pain, nausea | Mosquito nets and repellents, long-sleeved clothes, control of breeding, avoiding still water |
Explanation
The table shows how each disease spreads and how to stop it. Air-borne diseases need masks and covered faces. Water-borne ones need clean food and boiled water. Insect-borne ones need nets and no still water.
โ Summary
- Air-borne: cover mouth and nose.
- Water-borne: boil water, eat clean.
- Insect-borne: use nets, repellents.
- Vaccines help prevent many.
๐ NCERT Question 3 — Flu outbreak in your school
What should the school do during a flu outbreak, and how can you protect yourself and respond kindly to a sick classmate?
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๐ NCERT Question 4 — Travelling to a malaria area
What precautions help before, during, and after a trip to a malaria-prone city, and why do nets and repellents matter?
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๐ NCERT Question 7 — Bar graph of dengue cases
Make a bar graph of monthly dengue cases and find the peak months, the lowest months, and why cases rise in the monsoon.
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๐ NCERT Question 10 — Diseases from contaminated water
Which diseases may spread if drinking water gets contaminated by excreta from an infected person?
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