Biology · Lesson 23

Diseases you must know

JAMBWAECNECO

What the syllabus asks

JAMB: Ecology: diseases, their causes, vectors and control; immunity

WAEC: Diseases: causative agents, vectors, transmission, symptoms, prevention and control of common diseases (malaria, cholera, typhoid, tuberculosis, HIV/AIDS, river blindness, sleeping sickness, schistosomiasis, guinea worm, gonorrhoea, syphilis, measles, polio); immunity and vaccination; public health and sanitation

NECO: Diseases: causative agents, vectors, transmission, symptoms, prevention and control of common diseases (malaria, cholera, typhoid, tuberculosis, HIV/AIDS, river blindness, sleeping sickness, schistosomiasis, guinea worm, gonorrhoea, syphilis, measles, polio); immunity and vaccination; public health and sanitation

What you will learn

Distinguish pathogen, vector and host.
Classify diseases by their cause and route of spread.
Describe the cause, vector, symptoms and control of major Nigerian diseases.
Explain the life cycle of Plasmodium and how malaria control breaks it.
Explain types of immunity and how vaccines work.
Describe public health measures used in Nigeria.

Key points

Pathogen = cause; vector = carrier; host = victim.
Pathogen groups: virus, bacterium, protozoan, fungus, worm.
Malaria: Plasmodium (protozoan), female Anopheles; sporozoites injected; liver then red cells.
Cholera and typhoid: bacteria spread by faecal-oral route; prevent with safe water and sanitation.
TB: Mycobacterium, airborne; BCG vaccine; ventilation; boil milk.
Tsetse → sleeping sickness; blackfly → river blindness; Aedes → yellow fever; Culex → elephantiasis.
Schistosomiasis: snail intermediate host; larvae enter through skin.
HIV attacks helper T-cells; spread by sex, blood and mother to child; ART controls it.
Active immunity: own antibodies, long-lasting; passive: received antibodies, short-lived.
Public health: safe water, sanitation, vector control, immunisation, education, surveillance.

Start here: What is a disease?

A disease is any condition that disturbs the normal working of the body or one of its parts, producing signs (what a doctor can observe, like a high temperature) and symptoms (what the patient feels, like headache). Biologists sort diseases into two big groups.

Infectious (communicable) diseases are caused by pathogens and can pass from person to person: malaria, cholera, tuberculosis, measles.
Non-infectious (non-communicable) diseases are not caused by pathogens and cannot be "caught": diabetes, high blood pressure, sickle cell anaemia, kwashiorkor, goitre.

Non-infectious diseases themselves have different causes. Deficiency diseases come from lack of a nutrient: kwashiorkor (protein), rickets (vitamin D or calcium), scurvy (vitamin C), goitre (iodine), night blindness (vitamin A). Hereditary diseases are passed from parents through genes: sickle cell anaemia, haemophilia, albinism. Degenerative diseases come from the wearing out of body parts with age: arthritis, some heart disease. Lifestyle diseases are linked to habits: lung cancer from smoking, liver damage from alcohol, type 2 diabetes linked to diet and inactivity.

This topic focuses on infectious diseases, because they are the ones WAEC and JAMB test with causes and vectors, but you should be able to place any disease into the right group.

Worked example 23.1

Classify: (a) goitre, (b) cholera, (c) sickle cell anaemia, (d) tuberculosis.

Goitre is caused by lack of iodine, so it is non-infectious (deficiency).
Cholera is caused by a bacterium and spreads through water, so it is infectious.
Sickle cell anaemia is inherited through genes, so it is non-infectious (hereditary). You cannot catch it from a friend.
Tuberculosis is caused by a bacterium spread in droplets, so it is infectious.

(a) deficiency (b) infectious (c) hereditary (d) infectious

⚠️ Common mistake: calling sickle cell anaemia "contagious". It is inherited; the only way to "get" it is from both parents' genes.

Try it yourself. Which group does rickets belong to, and what causes it?

Show solution

A deficiency disease, caused by lack of vitamin D or calcium, giving soft, bent bones.

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Practice questions

1. The vector of malaria is the

female Anopheles mosquito
male Anopheles mosquito
female Culex mosquito
tsetse fly

Show answer

A: female Anopheles mosquito
Only females bite (they need blood for their eggs). Plasmodium is the cause.

2. Cholera is caused by a

virus
protozoan
fungus
bacterium

Show answer

D: bacterium
Vibrio cholerae, a bacterium, spread through contaminated water.

3. River blindness is transmitted by the

sandfly
tsetse fly
blackfly
housefly

Show answer

C: blackfly
Simulium (blackfly) carries Onchocerca volvulus.

4. Malaria is caused by

bacteria
Plasmodium
a virus
Anopheles mosquito

Show answer

B: Plasmodium
Anopheles is the vector; Plasmodium is the pathogen.

5. Which disease is caused by a virus?

Measles
Tuberculosis
Cholera
Malaria

Show answer

A: Measles
Measles is viral.

Key words

Disease: A condition that disturbs the normal working of the body.
Pathogen: An organism that causes disease.
Vector: An organism that carries a pathogen from one host to another.
Host: The organism in which a pathogen lives.
Infectious disease: A disease that can pass from one person to another.
Non-infectious disease: A disease not caused by a pathogen, e.g. diabetes, kwashiorkor.
Incubation period: Time between infection and the first symptoms.
Epidemic: A sudden spread of a disease to many people in an area.
Endemic: A disease always present in an area.
Pandemic: An epidemic that spreads across continents.
Antigen: A foreign substance that triggers an immune response.
Antibody: A protein made by white blood cells that targets a specific antigen.

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