What makes us ill, how germs spread, and how diseases are prevented and controlled.
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Health is a state of complete physical, mental and social well-being, not just the absence of disease. A disease is a disturbance of normal body function. Communicable (infectious) diseases pass from person to person and are caused by pathogens: viruses (common cold, influenza, dengue, AIDS, measles), bacteria (cholera, typhoid, TB), protozoa (malaria, amoebic dysentery), fungi (ringworm) and worms (tapeworm, roundworm). Non-communicable diseases do not spread; examples are diabetes, cancer, heart disease and deficiency diseases.
Differentiate communicable and non-communicable diseases.
Communicable diseases are caused by pathogens and spread between people. Non-communicable diseases do not spread, e.g. diabetes.
Name the pathogen type for (a) cholera, (b) malaria, (c) influenza, (d) ringworm.
(a) Bacterium. (b) Protozoan (Plasmodium). (c) Virus. (d) Fungus.
Is scurvy communicable? Explain.
No. It is a deficiency disease from lack of vitamin C; no germ spreads it.
Pathogens travel by air (droplets from cough or sneeze: cold, TB, influenza), contaminated water and food (cholera, typhoid, hepatitis A), direct contact (ringworm, scabies), body fluids (AIDS, hepatitis B) and vectors, animals that carry the pathogen. The female Anopheles mosquito carries the malaria parasite, and Aedes mosquitoes carry dengue. The time between infection and the first symptom is the incubation period.
Name the vector of (a) malaria, (b) dengue.
(a) Female Anopheles mosquito. (b) Aedes mosquito.
In an outbreak each patient infects 2 others per cycle, starting with 1 case. How many new cases appear in the 5th cycle?
Cases double each cycle: 2^5 = 32.
How can we reduce the spread of airborne diseases?
Cover the mouth when sneezing, avoid crowded closed rooms when ill, wear a mask and ventilate rooms.
Prevention is better than cure. Keep water and food clean, control vectors (drain stagnant water, use nets and repellents), isolate patients and vaccinate. The body's defences are skin, mucus, stomach acid and white blood cells, which engulf germs or make antibodies. Immunity is the body's ability to resist a disease. Vaccination gives immunity before infection. For an infection spreading with R₀ = 4 (each patient infects 4 others), about (1 − 1/4) × 100 = 75% of the population must be immune to stop it spreading.
If R₀ = 4, what percentage must be immune to stop an outbreak spreading?
(1 − 1/4) × 100 = 75%.
Name the first line of defence in the body.
Unbroken skin and the mucus and cilia of the respiratory tract.
What do white blood cells do against germs?
Some engulf germs (phagocytes) and others make antibodies.
1. Define health.
2. What are pathogens? Name two kinds.
3. Name two airborne diseases.
4. Which disease is caused by Plasmodium and spread by mosquitoes?
5. What is a vector?
6. What is the incubation period?
7. Name two non-communicable diseases.
8. How is dengue controlled?
9. One infected person passes a disease to 3 others, and each of them to 3 more, and so on. How many new cases appear in the 3rd round of spread?
10. Why is prevention better than cure?