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๐ฌ Think about it
When one person sneezes in a crowded bus, others may catch a cold. Germs travel — through air, touch, food, water, and even mosquito bites. They are like tiny travellers looking for a new home. How exactly do they spread, and how do we stop them? Let's find out.
How do communicable diseases spread?
How does a pathogen reach us?
Communicable diseases
Three routes of spread
Through the air
Coughs and sneezes
Example:
Common cold and influenza
Chickenpox
Measles
Tuberculosis
Through water and food
Contaminated food or water
Example:
Hepatitis A
Cholera
Typhoid
Ascariasis
Through insects
Carried by vectors
Example:
Malaria
Dengue fever
- Through air, when an infected person coughs or sneezes.
- Through direct contact, like shaking hands.
- Through contaminated food or water, or by insects.
What are vectors?
Vector
An insect
a mosquito or a housefly
Carries a pathogen
from an infected person to a healthy one
↓
A vector is an insect that carries a pathogen from one person to another.
- Vectors are insects that carry and spread pathogens.
- Mosquitoes and houseflies are common vectors.
- They pass germs from an infected person to a healthy one.
Example:
A mosquito carries the malaria parasite from a sick person to a healthy person through its bite.
๐ฌ
Activity 3.4 — Let us find out
How do we complete the disease table?
Start from the students’ list
Common communicable diseases, collected on a campaign and in the library
↓
Check every entry
In books, on trusted websites, or with your science teacher
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Add any missing details
Causal agent, site of infection, symptoms, preventive measures
↓
Study the finished table
And think about what prevents each disease
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The diseases sort into three routes: through the air, through water and food, and through insects
In this Activity, we will study a table of common communicable diseases and how each one is prevented.
What to do
Grade 8 students listed common communicable diseases in a table. Check the details using books, trusted websites, or your science teacher, and think about how to prevent each disease.
The table of diseases
| Disease | Causal agent | Site of infection | Spreads by | Symptoms | Preventive measures |
|---|---|---|---|---|---|
| Diseases spread through the air | |||||
| Common cold and influenza | Virus | Respiratory tract | Air | Nasal congestion and discharge, sore throat, fever, cough, body ache | Washing hands frequently, not sharing personal items, covering the mouth and nose |
| Chickenpox | Virus | Respiratory tract, skin | Air | Mild fever, itchy skin, rashes, blisters | Complete isolation of the patient, covering the mouth and nose, vaccination |
| Measles | Virus | Skin, respiratory tract | Air | Fever, sore throat, and reddish rashes on the neck, ears and other parts of the skin | Isolation of the patient, covering the mouth and nose, maintaining good hygiene, vaccination |
| Tuberculosis (TB) | Bacteria | Lungs | Air | Cough, fever, fatigue, loss of appetite, night sweats | Avoiding close contact with TB-infected people, covering the mouth and nose, maintaining good hygiene, getting vaccinated |
| Diseases spread through contaminated water and food | |||||
| Hepatitis A | Virus | Liver | Water & food | Fatigue, fever, loss of appetite, nausea, vomiting, jaundice, pain in the upper right abdomen | Drinking boiled water, vaccination |
| Cholera | Bacteria | Intestine | Water & food | Diarrhoea and dehydration | Maintain personal hygiene and good sanitary habits, consumption of properly cooked food and boiled drinking water, vaccination |
| Typhoid | Bacteria | Intestine | Water & food | Headache, abdominal discomfort, fever, and diarrhoea | Maintain personal hygiene and good sanitary habits, consumption of properly cooked food and boiled drinking water, vaccination |
| Ascariasis (roundworms) | Worms | Intestine | Water & food | Worms in stool, loss of appetite, poor growth, diarrhoea, weight loss, anaemia | Maintain personal hygiene and good sanitary habits, consumption of properly cooked food and boiled drinking water |
| Diseases transmitted by insects | |||||
| Malaria | Protozoa | Skin, blood | Insects (mosquito) | High fever, profuse sweating, periodic chills | Use of mosquito nets and repellents, wearing long-sleeved clothes, control of mosquito breeding in and around your home |
| Dengue fever (Break bone fever) | Virus | Skin, blood | Insects (mosquito) | Fever, headache, muscle and joint pain, nausea | Use of mosquito nets and repellents, wearing long-sleeved clothes, control of mosquito breeding in and around your home, avoiding areas with still water |
What we learn
Diseases spread by air, by water and food, or by insects. Knowing how each spreads helps us choose the right way to prevent it.
Communicable diseases spread through the air, through contaminated water and food, or through insects.
โ Summary
- Diseases spread by air, water-food, or insects
- Each has a causal agent and symptoms
- Knowing the spread helps prevention
What simple steps prevent communicable diseases?
| Precaution | How it protects |
|---|---|
| Keeping ourselves and our surroundings clean | Gives pathogens nowhere to grow |
| Practising basic hygiene every day | Stops germs reaching the mouth and nose |
| Washing hands with soap and water | Removes pathogens from the hands |
| Covering our mouth and nose while coughing or sneezing | Stops germs spreading through the air |
| Wearing a mask in crowded places | Blocks germs breathed out by others |
| Avoid sharing personal items like towels and handkerchiefs | Prevents spread by indirect contact |
| Keeping our home, food and water clean | Prevents food- and water-borne disease |
| Staying at home and resting when unwell | Helps recovery and protects other people |
- Keep ourselves and our surroundings clean, and practise hygiene.
- Wash hands with soap and cover the mouth while sneezing.
- Wear a mask in crowds and avoid sharing personal items.
- Stay home and rest when unwell to avoid spreading the disease.
What are parasites?
Parasite
Lives in or on
another living being
Feeds on it
taking the host’s nutrients
↓
A parasite is an organism that lives in or on another living being and feeds on it.
- Parasites are organisms that live in or on another living being.
- Some worms live in our digestive system and feed on our nutrients.
- They spread through contaminated food, water, soil, or contact.
Important Points
- Communicable diseases are caused by pathogens and can spread.
- They spread by air, contact, food, water, or insect vectors.
- Hygiene, masks, and clean food and water prevent them.
โ
Test Yourself
-
Which pathogen causes malaria?
View Answer
A protozoa, spread by the mosquito. -
Name a disease that spreads through contaminated water.
View Answer
Cholera, typhoid, or Hepatitis A. -
What is a vector?
View Answer
An insect, like a mosquito, that spreads pathogens. -
How does tuberculosis spread?
View Answer
Through air, from a TB-infected person. -
Why should we stay home when unwell?
View Answer
To rest and to avoid spreading the disease to others.
Important Definitions
- Pathogen — A disease-causing organism, such as a bacterium, virus, fungus, worm, or protozoa.
- Communicable disease — A disease caused by pathogens that can spread from one person to another.
- Vector — An insect, like a mosquito or housefly, that spreads pathogens.
- Parasite — An organism that lives in or on another living being and feeds off it.
๐ NCERT Question 3 — Flu outbreak in your school
There is a flu outbreak in your school. Several classmates are absent, while some are still coming to school coughing and sneezing.
View Answer →
๐ NCERT Question 4 — Travelling to a malaria area
Your family is planning to travel to another city where malaria is prevalent.
View Answer →
๐ NCERT Question 7 — Dengue cases bar graph
The following table contains the number of dengue cases reported in a hospital over one year: January 10, February 12, March 15, April 18, May 22, June 40, July 65, August 65, September 65, October 30, November 30, December 20.
View Answer →
๐ NCERT Question 10 — Diseases from contaminated water
Which disease(s) among the following may spread if drinking water gets contaminated by the excreta from an infected person? Hepatitis A, Tuberculosis, Poliomyelitis, Cholera, Chickenpox.
View Answer →
