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Common Diseases and Prevention ICSE Class 9 Biology

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BiologyICSE Class 9 · Health and Hygiene

Common Diseases: Bacterial, Viral, Protozoan and Helminthic (ICSE Class 9 Biology)

Updated 17 October 2026 · Fact-checked

Bacterial diseases include cholera, typhoid and tuberculosis; viral diseases include AIDS, chicken pox and hepatitis; protozoan diseases include malaria and amoebic dysentery; helminthic (worm) diseases include filariasis and ascariasis. Each has a causative agent, a mode of spread, symptoms and preventive measures.

Sort each disease by its causative agent: bacteria, virus, protozoan or worm, and remember that antibiotics do not work against viral diseases.

Illustration drawn for QuestionBuddy.

Understand Common Diseases: Bacterial, Viral, Protozoan and Helminthic

1. Bacterial diseases.

  • *Cholera*: *Vibrio cholerae*; spreads through contaminated water and food; severe watery diarrhoea and dehydration. Prevention: clean water, hygiene, vaccines; treatment: oral rehydration solution (ORS).
  • *Typhoid*: *Salmonella typhi*; contaminated food and water; prolonged fever, weakness, abdominal pain. Diagnosed by the Widal test; prevent by vaccination and hygiene.
  • *Tuberculosis*: *Mycobacterium tuberculosis*; spreads by droplets from coughing and sneezing; chronic cough, weight loss; BCG vaccine gives protection.

2. Viral diseases (antibiotics do not work against them).

  • *AIDS*: HIV attacks the immune system (T-helper cells), so the body cannot fight infections. Spread by unprotected sexual contact, infected blood or needles and from mother to child; not by hugging, sharing food or mosquito bites. Prevention: screened blood, sterile needles, safe practices, awareness.
  • *Chicken pox*: varicella virus; airborne and by contact; itchy fluid-filled blisters; a vaccine exists.
  • *Hepatitis*: viral infection of the liver causing jaundice; hepatitis A spreads through contaminated food and water, hepatitis B through blood and body fluids.

3. Protozoan diseases.

  • *Malaria*: *Plasmodium*, spread by the bite of the female *Anopheles* mosquito; fever with chills at intervals. Control: remove stagnant water, nets, repellents.
  • *Amoebic dysentery*: *Entamoeba histolytica*; contaminated food and water; stools with mucus and blood.

4. Helminthic diseases.

  • *Filariasis (elephantiasis)*: *Wuchereria*, spread by the *Culex* mosquito; swelling of limbs.
  • *Ascariasis*: *Ascaris*, taken in by contaminated food; abdominal pain and anaemia.

Common Diseases: Bacterial, Viral, Protozoan and Helminthic: key facts

Bacterial
CholeraVibrio cholerae
TyphoidSalmonella typhi
TBMycobacterium tuberculosis
Viral
AIDSHIV
Chicken poxvaricella
Hepatitisliver infection
Protozoan
Malaria: Plasmodium via Anopheles | Amoebic dysentery: Entamoeba histolytica
Worm
Filariasis: Wuchereria via Culex | Ascariasis: Ascaris

Common Diseases: Bacterial, Viral, Protozoan and Helminthic 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.

After a flood

Suppose a town has floods and the water supply is contaminated; many people develop loose motions, fever and body pain after a week.

Suggest the diseases and the first steps to reduce them.

Try it first, then show the solutionSolution
  1. Contaminated water suggests cholera, typhoid or amoebic dysentery.
  2. Boil or chlorinate drinking water, use ORS, wash hands.
  3. Remove stagnant water to prevent mosquito diseases.

Answer: Water-borne diseases; clean water, ORS and hygiene are the first steps.

Memory hook: Boil, cover, wash.

Tricks to remember Common Diseases: Bacterial, Viral, Protozoan and Helminthic

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

  • V-S-A

    Vibrio cholera, Salmonella typhoid, Anopheles malaria.

    Use it when: Pathogen-disease pairs.

  • HIV hits T

    HIV attacks T-helper cells.

    Use it when: AIDS question.

Common Diseases: Bacterial, Viral, Protozoan and Helminthic: solved examples

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

Example 1: Pathogens · 3 marks · Short answerBoard level

Name the causative organism of (a) cholera, (b) malaria, (c) elephantiasis. [3]

Try it first, then show the solutionSolution
  1. (a) Vibrio cholerae (bacterium).
  2. (b) Plasmodium (protozoan).
  3. (c) Wuchereria (worm).

Answer: (a) Vibrio cholerae (b) Plasmodium (c) Wuchereria.

Example 2: AIDS myths · 4 marks · Long answerHarder board level

State the three ways AIDS is spread, and two ways it is not. [4]

Try it first, then show the solutionSolution
  1. Spread by sexual contact, infected blood or needles and from mother to child.
  2. Not by shaking hands, hugging, sharing food or mosquito bites.

Answer: Sexual contact, blood or needles, mother to child; not by touch or mosquito.

Example 3: Malaria cycle · 3 marks · Short answerHarder board level

Explain why draining stagnant water helps to control malaria and filariasis. [3]

Try it first, then show the solutionSolution
  1. Mosquitoes lay eggs in stagnant water.
  2. Removing water breaks their life cycle.
  3. Fewer mosquitoes mean fewer infected bites.

Answer: It removes mosquito breeding places.

Example 4: Vaccine logic · 3 marks · Short answerHarder board level

Explain why a doctor prescribes ORS for cholera but not antibiotics for chicken pox. [3]

Try it first, then show the solutionSolution
  1. Cholera causes severe loss of water and salts; ORS restores them.
  2. Chicken pox is viral, and antibiotics act on bacteria only.
  3. Chicken pox is handled by rest and symptom relief; a vaccine prevents it.

Answer: ORS treats dehydration in cholera; chicken pox is viral so antibiotics are useless.

Example 5: Case: the dispensary · 5 marks · Case-basedHOTS / competency

Case. A dispensary sees patients with (P) fever at intervals with shivering, (Q) cough with weight loss for six weeks, (R) yellow eyes and weak liver. (i) Name each disease. [3] (ii) Which one can be controlled by BCG? [1] (iii) Which spreads through a vector? [1]

Try it first, then show the solutionSolution
  1. (i) P malaria, Q tuberculosis, R hepatitis.
  2. (ii) Tuberculosis.
  3. (iii) Malaria.

Answer: (i) Malaria, TB, hepatitis (ii) TB (iii) Malaria.

Where students lose marks in Common Diseases: Bacterial, Viral, Protozoan and Helminthic

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

  • Mistake: Writing that AIDS is spread by mosquitoes

    Common myth.

    Do this: State blood, sexual contact, mother to child.

    Usually costs: 1 mark.

  • Mistake: Naming Culex for malaria

    Vector names are swapped.

    Do this: Anopheles for malaria, Culex for filariasis.

    Usually costs: 1 mark.

  • Mistake: Suggesting antibiotics for viral diseases

    Pathogen type is ignored.

    Do this: Match treatment to pathogen.

    Usually costs: 1 mark.

Exam tips

  • Learn a table: disease, pathogen, spread, symptom, prevention.
  • Spell scientific names correctly.
  • For prevention write at least two measures.
  • State vector names where required.

Practice questions on Common Diseases: Bacterial, Viral, Protozoan and Helminthic

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

  1. Q1 · 1 mark · MCQBoard level

    Which disease is caused by a virus?
    (a) Typhoid
    (b) Tuberculosis
    (c) Chicken pox
    (d) Malaria

    Hint

    Pox.

    Answer

    (c) Chicken pox.

  2. Q2 · 1 mark · Very short answerBoard level

    Name the vector of malaria. [1]

    Hint

    Female.

    Answer

    Female Anopheles mosquito.

  3. Q3 · 2 marks · Very short answerBoard level

    Why is typhoid called a water-borne disease? [2]

    Hint

    Salmonella.

    Answer

    The bacterium spreads through water and food contaminated by faeces.

  4. Q4 · 1 mark · Assertion-reasonHarder board level

    Assertion (A): Antibiotics are useful in treating tuberculosis.
    Reason (R): Tuberculosis is caused by a bacterium.
    (a) Both A and R are true and R is the correct explanation of A.
    (b) Both A and R are true but R is not the correct explanation of A.
    (c) A is true but R is false.
    (d) A is false but R is true.

    Hint

    Pathogen type.

    Answer

    (a).

  5. Q5 · 3 marks · Short answerBoard level

    Differentiate between amoebic dysentery and cholera on cause and symptoms. [3]

    Hint

    Protozoan versus bacterial.

    Answer

    Amoebic dysentery: protozoan Entamoeba, stools with mucus and blood; cholera: bacterium Vibrio, watery diarrhoea and dehydration.

  6. Q6 · 3 marks · Short answerHarder board level

    Why is AIDS dangerous even though HIV does not kill the person directly? [3]

    Hint

    Immunity.

    Answer

    HIV weakens the immune system, so other infections and cancers cause death.

  7. Q7 · 2 marks · Very short answerHarder board level

    Why are filariasis patients advised to use mosquito nets? [2]

    Hint

    Vector.

    Answer

    The worm spreads by Culex mosquito bites; nets prevent bites.

  8. Q8 · 3 marks · Short answerHarder board level

    Compare a bacterial disease and a helminthic disease on cause, spread and one preventive measure each. [3]

    Hint

    Pair.

    Answer

    Typhoid: Salmonella, contaminated water, vaccination; ascariasis: Ascaris worm, contaminated food, washing hands and cooking food well.

  9. Q9 · 4 marks · Case-basedHOTS / competency

    Case. A village has repeated fever with chills every third day. (i) Name the probable disease and pathogen. [2] (ii) Suggest two community measures. [2]

    Hint

    Plasmodium.

    Answer

    (i) Malaria; Plasmodium. (ii) Drain stagnant water and spray insecticides; use nets.

  10. Q10 · 4 marks · Case-basedHOTS / competency

    Case. A person is diagnosed with HIV and wonders about eating with family. (i) Is it safe for the family to share food? [1] (ii) Give two reasons. [2] (iii) Why is counselling important? [1]

    Hint

    Myths.

    Answer

    (i) Yes. (ii) HIV does not spread by sharing food or by touch; it needs blood or body fluid contact. (iii) It reduces fear and stigma and supports treatment.

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. 1.Vaccine for TB?Show answer

    BCG.

  2. 2.Pathogen of AIDS?Show answer

    HIV.

  3. 3.Vector of filariasis?Show answer

    Culex.

  4. 4.ORS is for?Show answer

    Dehydration in cholera.

  5. 5.Test for typhoid?Show answer

    Widal test.

Common Diseases: Bacterial, Viral, Protozoan and Helminthic: frequently asked questions

Is malaria contagious from person to person?

Not directly; it needs the mosquito vector.

What is a pathogen?

An organism that causes disease.

Why wash hands?

To remove germs and worm eggs.