Biology and Health Sciences

Key unit
competence
To be able classify diseases and explain ways of preventing the spread of infectious diseases.

Cross-cutting issue

Comprehensive
sexuality education:

Rwandans need to ensure that they lead healthy lifestyles so that they can contribute to the Rwandan economy. HIV/AIDS is a serious disease that impacts on the lives of many Rwandans as well as the country’s economy.

At the end of this unit, you should be able to:

• Define good health as a state of mental, social and physical wellbeing
• Define disease as any physical or mental disorder or malfunction with a
characteristic set of signs and symptoms
• Explain how infectious diseases (cholera, tuberculosis, malaria, Ebola, HIV/
AIDS) are spread
• Explain ways in which infectious and non-infectious diseases can be
prevented
• Classify diseases into infectious, non-infectious, inherited, degenerative,
social, mental, eating disorder and deficiency diseases
• Adopt and encourage the practices that enhance good health
• Be aware that the clearing of bushes and grasses in the habitats of the
anopheles mosquitoes and the treatment of the stagnant water for the
anopheles larvae are necessary for eradicating malaria.

Oral activity

Some people are healthy, but others are sick. Sometimes sick people need to
go to hospital. In groups, talk about these questions.
1. What is good health?
2. Name some
diseases that
occur in your
community.
3. Discuss whether
or not people get
these diseases
from
other people.
4. Talk about ways
to prevent sick
people from
spreading disease.
5. Work out a
defi nition for the
terms ‘disease ’ and‘good health’. 

Topic 3: Health and disease

Health and disease When we say that a person is in ‘good health’, we mean that the person is in a good mental, physical and social state. The word ‘disease’ refers to a physical or mental disorder or malfunction that has a particular set of signs and symptoms. A person that has a disease is sick and may need to be treated by a health worker. Some diseases do not cause symptoms, so we may not know that the person is sick. However, other diseases cause a clear set of signs and symptoms.

Figure 11.3 A nurse taking care of a patient in hospital

Activity 11.1
Work on your own.
You may have heard the saying ‘prevention is better than cure’. Describe five
good practices that can prevent a person from getting
a disease.
Practices that promote good health
We can follow these good practices to prevent disease and stay healthy.
• Eat a balanced diet.
• Eat at regular intervals.
• Get enough sleep.
• Maintain good hygiene of the body, clothes, the home
and foods.
• Drink safe water.
• Exercise regularly.
• Avoid eating too much salt.
• Wash your hands before each meal and after going to
the toilet.

Activity 11.2
Work in groups.
Design a poster to show how washing your hands helps to prevent the spread of infectious diseases. Include information about how and when we must wash our hands.

Unit 11: Classification of diseases

Types of diseases
There are two main types of diseases: infectious and non-infectious
diseases.
Infectious diseases
Infectious diseases are diseases that are passed on, or transmitted, to a
person by another organism, such as a bacterium or virus. Organisms that
cause disease are called pathogens. They attack the body’s cells or release
poisons called toxins. Nearly all pathogens are micro-organisms, so they
are microscopic. When a person has an infectious disease, he or she can
spread it to another person. Table 11.1 lists some examples of pathogens
and the infectious diseases that they cause.
Table 11.1 Pathogens and infectious diseases

Topic 3: Health and disease

The spread and prevention of infections
You have learnt that infectious diseases can be transferred, or
transmitted, from one infected person to another. Another name for
an infectious disease is a communicable disease. Communicable
diseases are transmitted by infections.
Figure 11.7 A patient suffering from tuberculosis (TB), which is
an infectious disease
Infectious diseases can spread through:
• water (e.g. cholera); these are called
waterborne diseases
• air (e.g. measles, tuberculosis)
• blood (e.g. HIV/AIDS)
• sexual intercourse (e.g. gonorrhoea).
There are several ways to prevent the
spread of infectious diseases, including the
following:
• Inform and warn people about a
particular infectious disease, for
example, cholera or Ebola fever. Offer
health education at all levels of the
country.
• Improve public hygiene measures; for
example, remove the remains of dead
animals, have rubbish collection points
around schools and cities, and provide
safe drinking water and sewage systems.
• Isolate or quarantine infected people in
places where they have little contact with                                       
people other than health workers.
• Immunise people against infectious
diseases. This is an injection that
helps our bodies to fight a disease.
• Build more healthcare centres.

Unit 11: Classification of diseases

Activity 11.3
Work in groups.
1. What is an infection?
2. a) Find out the names of at least five infectious diseases.
b) Research how each of these diseases is transmitted, and then
suggest preventive measures for each one.

3. The wall chart below shows some ways to prevent cholera. Analyse it,
and then answer these questions.
a) Use the wall chart to suggest ways to prevent cholera.
b) Suggest any two other ways to prevent cholera.
c) How can we help someone with cholera?

Experiment 11.1
Work in pairs. Follow the steps on the next page to prepare an oral
rehydrating solution (ORS) that you can use as a first aid to help a patient
suffering from cholera. ORS is a mixture that is made from clean water,
table salt and sugar.

Topic 3: Health and disease

You will need: sugar (table sugar); table salt; two teaspoons; a clean onelitre
bottle with a lid; boiled water; a clean measuring cylinder or any
suitable container; soap
Procedure
1. Wash your hands with soap and water. Wash the teaspoons, bottle
and measuring cylinder with soap and clean water and leave them to
dry.
2. Put 750 ml of boiled water into the bottle.
3. Measure out one level teaspoonful of table salt. Remove half of the
salt from the spoon. Add the remaining half (2,5 ml) to the water in
the bottle.
4. Measure out one level teaspoon of sugar (use the other teaspoon to
level the sugar with the edge of the spoon). Add the teaspoonful of
sugar (about 5 ml) to the 750 ml of water in the bottle.
5. Repeat step 4 until you have added six level teaspoonsful (30 ml) of
sugar.
6. Put the lid on the bottle and shake it until all the sugar and salt
have dissolved. You have now prepared an oral rehydration solution
(ORS). Taste it; it should be no more salty than the tears from your
eyes.

Non-infectious diseases
Non-infectious diseases cannot be passed from one person to another by
living organisms. They develop because the body does not work properly,
or they may be caused by a person’s lifestyle. Examples include sickle cell
anaemia, allergies, ageing, osteoporosis, cancer, cardiovascular diseases,
eating disorders, deficiency diseases and mental illnesses.
Activity 11.4
Work on your own.
Kalisa and Nyirasafari still have their grandparents, who are 90 years old.
They like to visit their grandparents. One day, their grandmother fell and
broke her arm. The doctor said that her arm broke because of osteoporosis,
which is an age-related disease.
1. Do research in the library or on the Internet, and then explain the
words ‘ageing’ and ‘osteoporosis’.
2. What are the signs of ageing?
3. How can we take care of a person who is ageing?

Unit 11: Classification of diseases

Sickle cell anaemia
Sickle cell anaemia is a disease of the red blood cells. Sickle-shaped red
blood cells are unable to carry oxygen as well as normal red blood cells can.
They can also easily get stuck in narrow blood vessels. This prevents oxygen
from reaching the cells of the body.

Sickle cell anaemia is caused by a change in a gene that makes haemoglobin,
the molecules that give your blood its red colour. Haemoglobin helps red
blood cells to carry oxygen from the lungs to all the cells in the body.
The sickle cell gene is passed from one generation to the next. If both
a mother and father have the sickle cell gene and pass it to their child, then
their child will have sickle cell anaemia. If only one parent has the sickle cell
gene and it is passed to his or her child, then the child will be able to make
both normal and sickle cell haemoglobin. This child will be a carrier of the
sickle cell gene. There are tests available to find out if a child has sickle cell
anaemia. Although
there is no cure for sickle cell anaemia, medications can relieve
the symptoms.
Allergies
An allergy is a reaction by the immune system to a substance in the
environment. A substance that causes an allergy is called an allergen.
Some people are allergic to certain foods, for example, nuts or shellfish, or
to substances in the environment, for example, dust, pollen or pesticides.
When someone is allergic to something, they sneeze, get itchy eyes, get a
rash or have swelling on their body. There are different medicines available
to treat allergies.

Topic 3: Health and disease

Ageing
Ageing is the process of becoming older. Many
physical, mental and social changes take place. For
example, older people do not walk or think as fast as
younger people do. Ageing is a natural process that we
will all go through.
Osteoporosis
Osteoporosis is a bone disease that occurs mostly in
women after menopause. The bones become very
porous, and they break easily and heal slowly. The
disease can lead to curvature of the spine after the
vertebrae collapse.
Cancer
Cancer is a non-infectious disease that develops when cells of the
body do not divide normally. Cancer can start almost anywhere in a
person’s body. Cancer may lead to the growth of tumours. There are
many ways to treat cancer, but it is important to find it early on.
Cardiovascular diseases
These are diseases of the heart and blood vessels. Examples include
coronary heart disease (CHD) and strokes. CHD can lead to a heart
attack, which is when the heart muscles do not get enough oxygen. A
stroke occurs when too little oxygen is transported to the brain cells.
Eating disorders
Eating disorders lead to diseases that are caused by undereating or
overeating. You have already learnt about some diseases that occur
from undereating, such as kwashiorkor and marasmus.
Obesity is caused by eating more food calories than are used up
by physical activity. Excess energy is stored as fat. Obesity is becoming
more common as people eat more unhealthy ‘fast’ foods and spend
less time exercising.
Deficiency diseases
Deficiency diseases occur when a person’s diet lacks certain vitamins
and minerals. For example, a deficiency of vitamin C can lead to
scurvy. You learnt about some of these diseases in Unit 7 in Table 7.4,
on page 79.

Unit 11: Classification of diseases

Mental illnesses
Diseases that affect a person’s mind include depression, anorexia and
schizophrenia. There are many ways to treat these diseases. Table 11.2
summarises different types of diseases and gives examples of each disease.

Activity 11.5
Work in groups.
1. Look at the diseases given in the blocks below.

Put each disease into one of these categories:
a) infectious disease
b) non-infectious disease
c) inherited disease
d) eating disorder
e) deficiency disease.
2. Name four other diseases, and classify each disease into one of the
groups above.

Table 11.2 Different diseases and their descriptions

Topic 3: Health and disease

Exercise 11.1
Look at Table 11.2, on page 120, and then answer these questions.
1. Name:
a) three infectious diseases
b) two inherited diseases
c) one degenerative disease.
2. Give the meaning of the following terms:
a) degenerative disease
b) social disease
c) deficiency disease.
3. Which vitamin is deficient when a person has:
a) scurvy
b) rickets?

Activity 11.6
Work in pairs. Look at the photographs below, and then comment on the
health of each child.

Unit 11: Classification of diseases

Homework
1. List five types of diseases.
2. Explain the meaning of each of these terms.
a) infectious disease
b) hypertension
c) immunisation
d) haemoglobin
3. Copy the table below, and then complete it.

Checklist of learning
In this unit, I have learned that:
A person’s health includes their mental, social and physical well-being.
There are two main types of diseases: infectious and non-infectious diseases.
Infectious diseases are caused by pathogenic organisms, and they can be transmitted from one
person to another unless preventive measures are taken.
Preventing the spread of infectious diseases is important and includes quarantine
and immunisation.
Cholera is an infectious disease that is caused by a bacterium and spread through contaminated
water.
Some diseases are non-infectious; they include sickle cell anaemia, allergies, ageing, osteoporosis,
cancer, cardiovascular diseases, eating disorders, deficiency diseases and mental illnesses.

Topic 3: Health and disease

Peer assessment
1. Ask your partner to look at the pie chart, and then to tell you, according to the data presented,
which disease causes:
a) the most deaths b) the fewest deaths.

Number of deaths caused by the main non-infectious diseases worldwide
Source: http://www.who.int/gho/ncd/mortality_morbidity/ncd_premature_text/en
2. Describe to your partner two measures for preventing the spread of infectious diseases.
3. We often hear in the news that people in refugee camps die from cholera. Ask your partner to
explain factors that make cholera common in such camps.
4. a) Discuss with your partner the preventive measures the Rwandan government uses to eradicate
malaria.
b) Despite the measures taken by the government, malaria still causes the death of many
Rwandans. What factors are causing this failure to eradicate malaria?
5. The Rwandan government encourages its citizens to participate in sport. Discuss with your partner
the impact that sport can have on our health.

Unit 11: Classification of diseases