Disease Vectors


Many human diseases are caused by tiny living things. A patient carries in his or her body many of these tiny living things commonly called germs. A healthy person becomes sick if germs passed from a patient to the healthy person, grow inside the formerly healthy person.
In this article, you will study one important method by which germs are passed from one person to another by small living
organisms. These small living things that pass germs from one person to another are called vectors.

Passing of disease causing organisms from one person to another

These disease-causing organisms are passed
from one person to another through

i) direct contact;
ii) air, water, food or objects;
iii) other living things.

Passing of germs by direct contact

The germs that cause certain diseases such as leprosy, are passed from a patient to another person by direct body contact. The germs that cause such diseases are on the surface of the body of a patient. A healthy person, who has body contact with a patient, such as by a hand shake, hugging, brushing, or sleeping together may pick up the germs from the patient.

Diseases passed on by body contact are said to be contagious. Examples are ringworm, leprosy, small pox, measles.

Passing of germs through air, water, food
or objects.

A person that is sick of the common cold (or catarrh) breathes out the germs. Every time he or she breathes out, the germs remain alive in the air for sometime. If a healthy person, standing or sitting close to the patient breathes in the germs, the healthy person may become sick of the common cold.

A cholera patient passes out cholera causing germs in the stool. If such a person passes stool in a bush, the stool may dry up and break up into dust in the area. Ripe mangoes may fall in the area and pick up the cholera germs now mixed with the soil. These mangoes will become contaminated. Again rain water may wash the stool into a nearby stream which people of the area use for drinking. The water will become contaminated. A healthy person who uses this water for drinking or for washing hands before eating may suffer from cholera. Diseases which are passed on through the air water, food or objects are said to be infectious.

Passing of germs through living things

Almost every time people discuss malaria, they also talk about mosquitoes. There is a close link between the two.

This link will be described in detail as you read on. When a mosquito bites a malaria patient, it will in that process suck up, with the blood, germs that cause malaria. When that mosquito bites a healthy person, it will inject the malaria germs into the healthy person. This person may then suffer from malaria. An animal which passes germs from one person to another is called a vector.

Characteristics of a vector

A vector has four characteristics:
it is a small animal, sometimes an insect;

I) it passes germs from a person to another

ii) the germs grow and develop inside the vector to a stage that they can infect another person, when introduced into the person’s body;

ii) the vector is not made sick by the fact that it has the disease-causing germs in its body.

Malaria and Anopheles mosquito

Malaria is a very serious disease in the tropical and subtropical areas of Africa and other continents.

Economic effects of malaria

I) Malaria disease makes people under productive or unproductive.

ii) About 70% of all hospital patients are treated for malaria. This means that individuals and families are spending much money to keep themselves free of this disease.

III) Nigerian Government is spending billions of naira per year on efforts to control malaria, with programmes such as ‘Roll-back-malaria’.

iv) Malaria disease shortens people’s lives, especially the poor.

Life cycle of the female anopheles mosquito

The female anopheles mosquito is an insect. The life cycle has four stages: egg, larva, pupa and young adult imago). It is therefore said to have a complete metamorphosis.


The adult female anopheles mosquito lays her eggs singly in stagnant water (such as ponds, puddles, water collected in dirty gutters, cans, abandoned containers, leaf axils of cocoyams and bananas, damaged septic tanks and standing water tanks). Each egg has a boat shape, with two air floats to make it float in the water. In two days it hatches into a larva.


The larva is long, and lies parallel to the water surface, just under the water surface. It breathes atmospheric air through a breathing tube that projects above the water. It feeds on water plants and after 10 days changes into a pupa.


The pupa is comma shaped. It stays just below the water level, and breathes atmospheric air through two breathing tubes. It does not feed. In about seven days it changes into the young adult or imago.


The imago is like the adult but small. The total time for metamorphosis is about 21 days but this varies with temperature. In hot weather metamorphosis is faster than in cold weather.

Control of mosquitoes and malaria

The various ways of controlling mosquitoes and malaria can be described under the following headings:

i) Reduction of mosquito breeding sites

The living places where mosquitoes breed can be reduced by

a) clearing gutters, so that they do not
collect stagnant watery.

b) clearing empty cans in the

c) drying stagnant pools and ponds.

d) clearing tall grass around homes.

ii) Destruction of mosquitoes in the young stages

This can be done by:

a) spraying insecticides on standing

b) covering stagnant water with
kerosene or oil so that the mosquito larvae and pupae die because they cannot breathe.

iii) Killing of adult mosquitoes

Adult mosquitoes can be killed by

a) direct attack with brooms etc

b) using insecticides

iv) Preventing mosquito bites

This can be done by

a) using mosquito-proof nets to cover

b) sleeping under mosquito nets at

c) using insect repellents.

v) Preventing mosquitoes from reproducing

Female anopheles mosquitoes produce a
chemical which attracts male mosquitoes to come and mate with them.

These substances called pheromones, have been identified by scientists. They are now manufactured artificially. When a
pheromone is placed in a trap, male
mosquitoes stream into the trap. They
are killed in the trap with insecticides.

vi) Treatment of patients

Treatment of malaria patients with drugs
reduces the available infective malaria
germs to be passed from one person to

vii) Taking of drugs that prevent malaria

Daraprim is an example of a drug which,
taken as prescribed by a medical doctor.
prevents malaria. A person who takes
daraprim may not pass on the germs;
malaria parasites injected into that per-
son’s body die also.

Rex Nseobong

CEO and Founder of BabyNaija. My vision is to make the internet a place like home through BabyNaija.

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