BiologyICSE Class 8 · Health and Hygiene

Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation (ICSE Class 8 Biology)

Updated 17 October 2026 · Fact-checked

Communicable diseases spread from person to person through air, contact, blood or vectors. Influenza, measles, dengue, chikungunya and HIV are caused by viruses and malaria by the protozoan Plasmodium. A vector, such as the Anopheles or Aedes mosquito, carries the germ. Vaccination is the act of giving a vaccine; immunisation is the resulting protection.

Notice that the mosquito only carries the germ between people, so stopping its breeding and building immunity with vaccines breaks the chain.

Illustration drawn for QuestionBuddy.

Understand Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation

Communicable disease. A disease whose germ spreads from an infected person (or animal) to another. Causative agent = germ (virus, bacterium, protozoan); vector = a living organism, usually an insect, that carries the germ without itself being harmed.

Disease	Cause	Spread	Main symptoms	Prevention
Influenza	influenza virus	droplets of cough and sneeze	sudden fever, body ache, sore throat, cough	cover mouth when coughing; wash hands; flu vaccine
Measles	measles virus	droplets in air	fever, red watery eyes, red rash from the face	measles vaccine (MR or MMR); isolate the patient
Malaria	Plasmodium (protozoan)	bite of female Anopheles	high fever with chills at intervals, sweating, headache	nets, repellents, no stagnant water, insecticide spray
Dengue	dengue virus	female Aedes (daytime biter)	high fever, severe headache, pain behind the eyes, joint pain	empty coolers and pots weekly; cover water; full sleeves
Chikungunya	chikungunya virus	female Aedes	sudden fever, severe joint pain and swelling	same as dengue
HIV infection	HIV	unsafe sexual contact, infected blood, shared needles, infected mother to baby	weakens defence system; later repeated infections (AIDS)	tested blood, new disposable syringes, awareness

HIV does not spread by handshakes, hugs, shared food, toilets, playing or mosquito bites.

Only female mosquitoes bite, because they need blood to develop eggs. Stagnant water is where they lay eggs.

General prevention. Boil or filter water; clean food covered from flies; wash hands with soap; clean surroundings and garbage disposal; control vectors; isolate patients and cover coughs; balanced diet, exercise and rest; vaccination.

Vaccine. A preparation of dead or weakened germs (or parts) that makes the body produce antibodies without causing the disease. Edward Jenner made the first vaccine, against smallpox.

Vaccination	Immunisation
act of giving a vaccine (injection or drops)	process of becoming immune (protected)
single event	takes days or weeks; boosters may be needed
the cause	the result

Immunity can also follow natural recovery from some diseases.

Flow chart: vector-borne disease. Infected person → mosquito bites → germ enters the mosquito → mosquito bites a healthy person → germ enters blood → disease.

Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation: key facts

Causes: Virus: influenza, measles, dengue, chikungunya, HIV | Protozoan: Plasmodium for malaria; Germ is the cause; mosquito is the vector.
Vectors: Anopheles: malaria, night | Aedes: dengue and chikungunya, day, clean water; Only females bite.
Vaccination and immunisation: Vaccination giving the vaccine
Immunisation protection developed
Vaccine weakened germs
Antibodies made; Cause versus result.

Vaccination	giving the vaccine
Immunisation	protection developed
Vaccine	weakened germs
	Antibodies made

How to answer Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation questions

Typical items: complete the disease table, define a vector, state routes of spread, differentiate vaccination and immunisation, or recommend steps for a given outbreak.

1Name the causative agent first and the vector next; do not call the mosquito the cause.
2Match the vector to its habit: Anopheles at night in stagnant water; Aedes by day in clean stored water.
3For prevention, give the step that breaks the route of spread.
4For HIV, list the four routes, and say that casual contact is safe.
5For vaccination and immunisation, give act versus process.

Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Water in the cooler

Suppose a family finds several mosquito wrigglers in water collected in the tray of an old air cooler, and a neighbour has just had dengue.

What should the family do and why?

Try it first, then show the solutionSolution

Aedes mosquitoes lay eggs in clean, stored water.
Emptying and drying the tray weekly breaks the life cycle.
They should also cover water tanks and use repellents or full sleeves.

Answer: Empty the cooler tray weekly and cover water: it removes the breeding place of Aedes.

Memory hook: No standing water, no breeding.

A school outbreak

Suppose 18 of the 60 students in a class have a sudden fever, body ache and cough within three days.

Name the likely disease, calculate the percentage of students affected, and suggest two steps for the school.

Try it first, then show the solutionSolution

Fever, body ache and cough spreading fast suggest influenza.
Percentage = 18 ÷ 60 × 100 = 30%.
Send sick students home, cover coughs and sneezes, and wash hands.

Answer: Influenza; 30% affected; isolate sick students and practise cough hygiene.

Memory hook: Droplets spread in crowds.

Tricks to remember Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation

Short memory aids. Say each one aloud once, then use it on a question the same day.

Cause carries no wings
The germ causes; the mosquito only carries.
Use it when: Cause versus vector.
Aedes in the day, Anopheles at night
A for Aedes is the Afternoon biter of dengue; Anopheles bites after dusk.
Use it when: Vector habits.
Vaccination is the verb
You vaccinate (act), then become immune (result).
Use it when: Difference.

Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Vector of malaria · 1 mark · MCQBoard level

The vector of malaria is the:
(a) male Anopheles (b) female Anopheles (c) female Aedes (d) housefly

Try it first, then show the solutionSolution

Only female Anopheles bites and carries Plasmodium.

Answer: (b).

Example 2: Define vector · 2 marks · Short answerBoard level

Define a vector and give two examples of diseases for which a mosquito is the vector.

Try it first, then show the solutionSolution

A vector is a living organism, usually an insect, that carries disease germs from one host to another (1 mark).
Malaria and dengue (or chikungunya) (1 mark).

Answer: Carrier of germs; malaria, dengue.

Example 3: Table row · 4 marks · Long answerHarder board level

Write the causative agent, vector, two symptoms and two preventive measures for dengue, and say how chikungunya differs in its main symptom.

Try it first, then show the solutionSolution

Cause: dengue virus; vector: female Aedes mosquito (1 mark).
Symptoms: sudden high fever, severe headache, pain behind the eyes, joint pain (any two) (1 mark).
Prevention: empty and cover stored water, full sleeves, repellents (any two) (1 mark).
Chikungunya has the same vector but its main feature is severe joint pain and swelling that may last weeks (1 mark).

Answer: Dengue virus, Aedes; fever, headache; empty water; chikungunya shows severe joint pain.

Example 4: Vaccine at work · 3 marks · Short answerHarder board level

Explain how a vaccine protects a child from a disease, and say why a booster dose may be needed.

Try it first, then show the solutionSolution

A vaccine contains dead or weakened germs that cannot cause the disease (1 mark).
The body makes antibodies against them, so the real germ is destroyed quickly if it attacks later (1 mark).
Some vaccines give weak or short protection, so a booster dose is given to strengthen immunity (1 mark).

Answer: Weakened germs make antibodies; boosters strengthen protection.

Example 5: Two fevers · 4 marks · Case-basedHOTS / competency

Patient X has high fever with chills coming back every second day; Patient Y has a sudden high fever, severe joint pain, and pain behind the eyes after being bitten in the day. (a) Suggest the disease of each. (b) Name the vector of each. (c) Say why a net alone protects X better than Y. (d) Give one step common to preventing both.

Try it first, then show the solutionSolution

(a) X: malaria; Y: dengue (1 mark).
(b) X: Anopheles; Y: Aedes (1 mark).
(c) Anopheles bites mostly at night, when a net protects; Aedes bites in the daytime (1 mark).
(d) Remove stagnant water or use repellents (1 mark).

Answer: Malaria and dengue; Anopheles and Aedes; nets help against night biting; remove stagnant water.

Where students lose marks in Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation

The slips examiners see most often, and what to write instead.

Mistake: Saying malaria is caused by a mosquito
Vector and cause are confused.
Do this: Plasmodium causes; the mosquito carries.
Usually costs: 1 mark.
Mistake: Swapping Aedes and Anopheles
Both are mosquitoes with similar names.
Do this: Aedes: dengue, day; Anopheles: malaria, night.
Usually costs: 1 mark.
Mistake: Using vaccination and immunisation as the same
Both relate to protection.
Do this: Act versus process.
Usually costs: 1 mark.
Mistake: Wrong routes of HIV
Casual contact or mosquito bite is listed.
Do this: Learn the four routes and the safe activities.
Usually costs: 1 mark.

Exam tips

Table format: disease, cause, vector or spread, symptoms, prevention.
Only female mosquitoes bite.
Vaccination is the act; immunisation is the result.
HIV does not spread by casual contact.

Practice questions on Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · Very short answerBoard level
Name the causative agent of measles.
Hint
A virus.
Answer
The measles virus.
Q2 · 1 mark · Assertion-reasonHarder board level
Assertion (A): A person cannot get HIV by sharing a meal with an infected person.
Reason (R): HIV spreads only through contact with infected blood and certain body fluids, not through food.
(a) (A) is true and (R) is false.
(b) (A) is false and (R) is true.
(c) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(d) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
Hint
Routes of spread.
Answer
(c).
Q3 · 3 marks · Short answerHarder board level
Why are only female mosquitoes responsible for spreading diseases? Name one disease for each of the two mosquito types.
Hint
Blood and eggs.
Answer
Only females bite because they need blood to develop their eggs. Female Anopheles carries malaria and female Aedes carries dengue or chikungunya.
Q4 · 4 marks · Long answerHarder board level
Write the differences between vaccination and immunisation (three points), and say what a vaccine contains.
Hint
Act and result.
Answer
Vaccination is the act of giving a vaccine, while immunisation is the process of developing protection. Vaccination is a single event; immunisation takes days or weeks and may need boosters. Vaccination is the cause; immunisation is the result. A vaccine contains dead or weakened germs, or parts of them.
Q5 · 3 marks · Case-basedHOTS / competency
Read and answer.
Suppose a town reports 40 cases of dengue in a week, with many mosquito wrigglers in water tanks, flower vases and old tyres.
(a) Name the vector. (1)
(b) Give two actions the town should take. (1)
(c) Say why spraying alone may not stop the disease. (1)
Hint
Breeding places.
Answer
(a) Female Aedes. (b) Empty or cover stored water, clear tyres and vases weekly. (c) New mosquitoes keep hatching in standing water, so the breeding places must be removed.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.Which protozoan causes malaria?Show answer
Plasmodium.
2.Which mosquito spreads dengue?Show answer
Aedes.
3.Who made the first vaccine?Show answer
Edward Jenner.
4.Which vaccine protects against measles?Show answer
The MR or MMR vaccine.
5.What does a vaccine make the body produce?Show answer
Antibodies.

Communicable Diseases, Vectors, Prevention, Vaccination and Immunisation: frequently asked questions

Is influenza the same as the common cold?

They are different viral illnesses; influenza usually brings sudden fever and body ache.

Is the table detail required?

Yes, the syllabus asks for causative agents, symptoms and prevention in tabular form.

Are bacterial diseases asked?

The listed diseases are influenza, measles, malaria, dengue, chikungunya and HIV.

Where are tobacco and first aid covered?

In the next topic.