SCI/P/4: VECTORS AND DISEASES

This unit is about Vectors and diseases in Primary Four Science.

VECTORS AND DISEASES

Vocabulary

Vectors

Germs

Life cycle

Pupa

Larva

Adult

Parasites

Meaning of vectors

  • A vector is a living organism which spreads diseases.

Where some vectors are found

  • In latrines
  • In bushes
  • Near water sources
  • Vectors are found in decayed things like rotten food and human faeces.

Examples of disease vectors

Some vectors spread germs through bites on people. For example;

  • Dogs
  • Mosquitoes
  • Tsetse flies

Most vectors are insects. For example;

  • Mosquitoes
  • Tsetse flies
  • House fly
  • Flea
  • Bed bug
  • Cockroach
  • Biting
  • Lice
  • Ticks

WATCH THE VIDEO BELOW TO LEARN MORE ABOUT VECTOR BORNE DISEASES AND THEY CAN BE CONTROLLED


Disease and their vectors

Vector Disease carried
–          Female anopheles mosquito

–          Culet mosquito

–          Aides / tiger mosquito

–          Housefly

 

–          Bed bug

–          Tsetse fly

–          Flea

–          Cockroach

–          Louse

–          Ticks

–          Rats fleas

–          Malaria

 

 

–          Elephantiasis

 

–          yellow fever

 

–          diarrhoea,trachoma,dysentery,typhoid,cholera, polio

–          Itches and sores on the body

–          Sleeping sickness

–          Plague

–          Diarrhea, cholera, dysentery

–          Relapsing fever

–          Typhus fever

–          Bubonic plague

Houseflies

A housefly is an insect vector.

Its body is covered with hair.

Houseflies lay their eggs on faeces, decaying matter, dead animals, left over foods, etc.

A housefly carries germs on its hairy body.

STRUCTURE OF A HOUSE FLY

Diseases spread by houseflies

  1. Trachoma
  2. Diarrhoea
  3. Cholera
  4. Dysentery
  5. Typhoid

Lifecycle of a housefly

  1. A housefly undergoes four stages of development.
  2. It has a complete lifecycle.

housefly

  • The larvae stage of a housefly is called a maggot.
  • A maggot is very active; it moves and feeds a lot.
  • Maggots move by wriggling.
  • The pupae stage does not feed. It is dormant.

LIFE CYCLE OF A HOUSE FLY IN VIDEO EXPLAINED

Prevention of houseflies

  1. Spraying using insecticides.
  2. Keep houses clean.
  3. Keep cooked food covered.
  4. Proper disposal of faeces.
  5. Keep latrines properly covered.
  6. Proper disposal of rubbish.

Tsetse flies

Tsetse flies feed on blood

A tsetse fly crosses its wings when it is at rest

Tsetse flies are found in bushy areas, forested areas and near water sources.

A tsetse fly has a sharp proboscis which sucks blood.

Tsetse flies spread sleeping sickness in people and angina in animals like cows, goats and sheep.

tsetse fly

Lifecycle of a tsetse fly

A tsetse fly undergoes a complete lifecycle

Eggs of a tsetse fly hatch into maggots inside a female tsetse fly

A female tsetse fly passes out maggots on the ground.

Maggots make holes in the ground and change into pupae.

The pupae in turn develop into adult tsetse flies.

fly

TSETSE FLIES LIFE CYCLE IN VIDEO

Sleeping sickness

  • Sleeping sickness is caused by parasites called trypanosomes
  • It is spread by infected tsetse flies
  • It is called sleeping sickness in people and angina in animals

Signs of sleeping sickness

  1. Loss of weight
  2. A person fails to walk

WHAT IS SLEEPING SICKNESS? THE VIDEO BELOW GIVES DETAILS OF THE DISEASE

Symptoms

  • Body weakness
  • A person feels sleepy
  • Loss of appetite
  • Fever from time to time

Ways of controlling tsetse flies

  • Using tsetse fly traps
  • Spraying with insecticides
  • Clearing bushes near homes
  • Avoid very early and late grazing of animals

N.B.    Tsetse flies are very active when there is little sunshine.

TYPES MOSQUITOES

There are three types of mosquitoes namely;

  1. Culex mosquitoe
  2. Anopheles mosquitoes.
  3. Tiger or aedes mosquito.
mosquito disease Causative germ
Female anopheles malaria plasmodium
tiger Elephantiasis

 

Filarial worm
 aedes Yellow fever(dengue fever) virus

HOW ARE THE ABOVE DISEASES SPREAD?

They are spread through bites of infected adult mosquitoes.

Characteristics of mosquitoes.

  1. They have the proboscis for biting and sucking.
  2. They lay eggs in stagnant water.
  3. They are very active at dawn and dusk.

Lifecycle of a culex mosquito

A mosquito undergoes four stages of development, that is, complete metamorphosis.

A female mosquito lays eggs which hatch into larvae. The larvae stay in stagnant water until they grow into pupae.

At the pupae stage, the insect does not feed but move in water. The movement of pupae in water is called wriggling.

The pupae then grow into an adult mosquito.

culex mosquito

NB: -the larva stage lies at an angle of 45 degrees to the water surface and it uses siphones ( breathing trumpets) for breathing.

The adult lies parallel to the ground while at rest.

Lifecycle of an anopheles mosquito

anopheles

NB: – the larva stage lies parallel to the water surface.

  • The adult lies at an angle of 45 degrees to the ground surface while at rest.
  • A mosquito undergoes four stages of development, that is, complete metamorphosis.
  • A female mosquito lays eggs which hatch into larvae. The larvae stay in stagnant water until they grow into pupae.
  • At the pupae stage, the insect does not feed but move in water. The movement of pupae in water is called wriggling.
  • The pupae then grow into an adult mosquito.

WATCH THE VIDEO BELOW TO LEARN MORE ABOUT THE LIFE CYCLE OF MOSQUITOES

N.B.   Do you notice the difference in the eggs, larvae and adult stages in the two types of mosquitoes?

  1. 1. Draining stagnant water with in the compound.
  2. Spraying to kill adult mosquitoes.
  3. Slashing tall grass around the compounds.
  4. Oiling stagnant water in the compound.
  5. Removing broken bottles and empty tins in the compound

Control of malaria:

  • Sleeping under treated mosquito nets
  • Using repellents such as odomos creams to prevent mosquito bites.
  • Use of ant malarial tablets.

Feeding habits of mosquitoes.

Female anopheles mosquito feeds on blood from animals.

The male anopheles mosquito feeds on juice from plants.

Female culex mosquitoes feed on blood.

The male culex mosquitoes feed on juice from flowers.

NB: All female mosquitoes are able to spread diseases to human beings because they feed on blood.

Cockroaches

Characteristics of cockroaches:

  • They have hairy bodies.
  • Their bodies are broad and flat.
  • They have small heads with chewing mandibles on the bottom
  • They have long antennae.
  • They have legs with spines which help them move on surfaces.
  • They are nocturnal i.e they are active at night and hide at day time.

Diseases spread by cockroaches

  1. Diarrhoea
  2. Typhoid
  3. Dysentery
  4. Cholera
  5. Polio

Feeding habits of cockroaches.

  • Cockroaches use mandibles for feeding.
  • They feed on leftover food, cloth etc

Habitats of a cockroach.

  • In pit latrines
  • Under rocks
  • Follen trees
  • Under leaves.
  • In cracks of walls
  • In cupboards

Life history of cockroaches

It undergoes an incomplete metamorphosis.

The lifecycle of a cockroach

Cockroach-1

  • A female cockroach has an egg sac.
  • The egg sac contains 30 to 40 eggs in it.
  • The eggs hatch into the nymph.
  • The nymph develops into the adult in 3 to 4 months.

Controlling of cockroaches

  • Spraying with insecticides to kill cockroaches.
  • Maintain proper sanitation.
  • Use of borax
  • Keep the kitchen clean
  • Sweep the house and keep it clean.
  • Keep water covered
  • Keep food covered.
  • Seal cracks on walls.

WHAT IS A COCKROACH AND ITS LIFECYCLE

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