Unit 11 Classification of diseases
Key unit competence: Analyse different types of diseases, their spreading and preventive measures.
Key ideas
- Health (WHO): a state of complete physical, mental and social well-being, and not merely the absence of disease. A disease is a disorder of the body or mind with particular signs (seen or measured by others: fever, rash, swelling) and symptoms (felt by the patient: pain, headache, tiredness).
- Infectious (communicable) diseases are caused by pathogens and can spread from person to person: bacteria (cholera, typhoid, tuberculosis), viruses (HIV/AIDS, influenza, measles, Ebola, COVID-19), protoctists (malaria, amoebic dysentery, sleeping sickness), fungi (ringworm, athlete's foot, thrush) and worms (bilharzia).
- Spread: water and food (cholera, typhoid: drink boiled/treated water, wash hands, use latrines); air droplets (TB, flu, COVID-19, measles: cover coughs, ventilate, vaccinate); vectors such as the female Anopheles mosquito (malaria: sleep under treated nets, remove stagnant water, spray); blood and sexual contact (HIV: abstinence, faithfulness, condoms, never share sharp objects, screened blood); body fluids of sick people (Ebola: isolate patients, protective clothing, safe burials).
- Signs and symptoms: cholera: profuse watery "rice-water" diarrhoea, vomiting, severe dehydration; malaria: fever with chills and sweating, headache, body aches; Ebola: sudden fever, weakness, vomiting, diarrhoea, sometimes bleeding; HIV/AIDS: weight loss, long fever, chronic diarrhoea, repeated infections. Dehydration is treated with oral rehydration solution (ORS): clean boiled water with salt and sugar.
- Non-infectious diseases are not passed by pathogens: inherited (sickle cell anaemia, haemophilia), deficiency (scurvy, rickets, kwashiorkor), degenerative/ageing (arthritis, osteoporosis), lifestyle (obesity, type 2 diabetes, high blood pressure, heart disease, stroke, many cancers), allergies (to pollen, dust, some foods) and mental illnesses.
- Sickle cell anaemia is inherited: a changed gene makes abnormal haemoglobin, so red cells become sickle-shaped, carry less oxygen and block small vessels. A child with the gene from both parents has the disease; with the gene from one parent the child is a carrier.
- A physical disorder affects the body (asthma, diabetes, malaria, a fracture). A mental disorder affects thinking, mood and behaviour (depression, anxiety, schizophrenia, post-traumatic stress). Signs include long-lasting sadness, fear, poor sleep, withdrawal and loss of interest. People with mental disorders need care, support and treatment, not isolation or mockery.
- Ways to prevent infectious diseases: health education, clean water and sanitation, waste collection, vaccination, isolating or quarantining sick people, early diagnosis and treatment, personal hygiene. Good health also needs a balanced diet, exercise, sleep and social connection.
Common misconceptions
- "All diseases are caused by germs." No: inherited, deficiency, lifestyle and degenerative diseases are not caused by pathogens.
- "Malaria spreads from person to person through the air." No: it is spread by the bite of an infected female Anopheles mosquito.
- "You can tell from someone's appearance that they have HIV." No: a person may look healthy for years; only a test shows HIV infection.
- "Mental illness is a sign of weakness or a curse." No: it is a health condition that can be treated with medical and social support.
Worked examples
Example 1. Classify these diseases as infectious or non-infectious and name the cause of each infectious one: cholera, sickle cell anaemia, malaria, obesity, tuberculosis.
Solution
Infectious: cholera (bacterium), malaria (protoctist Plasmodium carried by Anopheles mosquito), tuberculosis (bacterium). Non-infectious: sickle cell anaemia (inherited), obesity (lifestyle).
Example 2. Explain how to make ORS at home and why it is given to a person with cholera.
Solution
Mix 1 litre of clean, boiled and cooled water with 6 level teaspoons of sugar and half a level teaspoon of salt. Cholera causes rapid loss of water and salts in diarrhoea; ORS replaces them and prevents death from dehydration until medical help is reached.
Practice questions
Define health, disease, sign and symptom.
Show answer
Health: complete physical, mental and social well-being, not just absence of disease. Disease: a disorder of body or mind with particular signs and symptoms. Sign: a change others can see or measure (fever, rash). Symptom: what the patient feels (pain, headache).
Common mistake: Defining health only as "not being sick".
Give one example of a disease caused by each: bacterium, virus, protoctist, fungus.
Show answer
Bacterium: cholera/TB/typhoid. Virus: HIV/influenza/measles/Ebola. Protoctist: malaria. Fungus: ringworm/athlete's foot.
Common mistake: Saying malaria is caused by a virus.
Describe how malaria is spread and give three ways to prevent it.
Show answer
An infected female Anopheles mosquito bites a person and passes Plasmodium into the blood. Prevention: sleep under treated nets; remove stagnant water; spray insecticide; wear long clothes in the evening; get early treatment.
Common mistake: Saying malaria spreads by drinking dirty water.
State the signs of cholera and explain how to prevent it.
Show answer
Signs: profuse watery diarrhoea, vomiting, dehydration, muscle cramps. Prevention: drink boiled or treated water, wash hands with soap, use latrines, cover and cook food well, vaccination in outbreaks.
Common mistake: Listing malaria symptoms for cholera.
Distinguish between infectious and non-infectious diseases with two examples each.
Show answer
Infectious: caused by pathogens and can spread (cholera, TB). Non-infectious: not caused by pathogens and do not spread (sickle cell anaemia, obesity, diabetes).
Common mistake: Giving rickets as infectious.
Distinguish between physical and mental disorders with one example each.
Show answer
Physical disorder affects the body or organs (asthma, diabetes). Mental disorder affects thinking, feelings and behaviour (depression, anxiety).
Common mistake: Saying mental disorders are not real illnesses.
Explain three ways HIV can be transmitted and three ways to prevent it.
Show answer
Unprotected sex with an infected person; infected blood or sharing needles and razors; mother to child during birth or breastfeeding. Prevention: abstinence or faithfulness and condoms; never share sharp objects, use screened blood; prevention of mother-to-child transmission programmes.
Common mistake: Saying HIV spreads by mosquitoes, hugging or sharing food.
Give five ways a community can reduce the spread of infectious diseases.
Show answer
Health education; safe water and sanitation; vaccination; isolating sick people; early diagnosis and treatment; waste collection and clean surroundings; hand washing.
Common mistake: Listing only personal hygiene.
Matching and drag-and-drop
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. Malaria is caused by a: a. female Anopheles mosquito 2. Obesity and type 2 diabetes are mainly linked to: b. protoctist 3. ORS is given to a person with diarrhoea to: c. replace lost water and salts 4. The vector that transmits malaria is the: d. poor diet and lack of exercise Show answer
1 → b (protoctist) · 2 → d (poor diet and lack of exercise) · 3 → c (replace lost water and salts) · 4 → a (female Anopheles mosquito)
- The parasite lives in red blood cells.
- They are non-communicable lifestyle diseases.
- It prevents dehydration.
- Only females feed on blood.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
contaminated water and food · faeces contaminate drinking water and food · people cough more in crowded tents · pathogen- An organism that causes disease is a .
- In a refugee camp with few latrines and unsafe water, cholera spreads quickly because .
- Cholera is spread mainly through .
Show answer
1: pathogen · 2: faeces contaminate drinking water and food · 3: contaminated water and food
- Bacteria, viruses, protoctists and fungi can be pathogens.
- Cholera is a waterborne disease spread by the faecal-oral route.
- Vibrio cholerae lives in water contaminated by faeces.
Matching
Match each item in column A with the correct answer in column B. Write the letter next to each number.
Column A Column B 1. Scurvy and rickets are examples of: a. mosquitoes lay their eggs in stagnant water 2. According to WHO, health is: b. physical, mental and social well-being 3. Ringworm is caused by a: c. fungus 4. Removing stagnant water around homes reduces malaria because: d. deficiency diseases Show answer
1 → d (deficiency diseases) · 2 → b (physical, mental and social well-being) · 3 → c (fungus) · 4 → a (mosquitoes lay their eggs in stagnant water)
- They result from lack of vitamins C and D.
- Health is more than just not being ill.
- Despite its name, ringworm is a fungal skin infection.
- Fewer breeding sites mean fewer mosquitoes.
Drag and drop
Choose the correct word or phrase from the box for each gap. One word in the box is not needed.
inherited · vaccine · air droplets from coughing · toxin- Tuberculosis spreads mainly through .
- A disease caused by a faulty gene passed from parents is .
- An injection that helps the body fight a particular disease is a .
Show answer
1: air droplets from coughing · 2: inherited · 3: vaccine
- Covering coughs and ventilation reduce spread.
- Examples: sickle cell anaemia, haemophilia.
- Vaccination prevents measles, polio, TB and others.